LED based trough designed mechanically steerable beam traffic signal

FIELD OF THE INVENTION

The present invention is generally related to light sources, and more particularly to traffic signal lights including those incorporating solid state light sources.

BACKGROUND OF THE INVENTION

Traffic signal lights have been around for years and are used to efficiently control traffic through intersections. While traffic signals have been around for years, improvements continue to be made in the areas of traffic signal light control algorithms, traffic volume detection, and emergency vehicle detection.

One of the current needs with respect to traffic signal lights is the ability to generate a homogenous narrow light beam, that is, a coherent light beam having a uniform intensity thereacross. Conventional incandescent lights tend to generate a light beam having a greater intensity at the center portion than the outer portions of the light beam. With respect to current solid state light sources, while LED arrays are now starting to be implemented, the light output of these devices can have non uniform beam intensities, due to optics and when one or more LEDs have failed.

One current approach to adjust the viewing angle of an incandescent traffic signal is to simply mask the active area of an incandescent illuminated diffuser. The masking is typically accomplished by the use of a reflective tape similar to duct tape. This approach is tedious, trial-and-error, and problematic.

There is desired an improved solid state light source generating and steering a homogenous light beam.

SUMMARY OF THE INVENTION

The present invention achieves technical advantages as a solid state light generating a homogenous steerable light beam particularly useful in traffic control signals.

The solid state light includes a housing having a cavity, an area array of light emitting diodes (LEDs) disposed in the housing cavity and generating a light beam, and a lens disposed over the LED area array transmitting the received light beam. Advantageously, a mask is selectively positionable over the cavity and selectively blocks a portion of the light generated by the LEDs to thereby responsively control a direction of the light beam transmitted through the lens. The unmasked light beam is transmitted through the lens at an angle being a function of a position of the mask and the lens optics. Preferably, the housing cavity has light reflective side walls and a light diffuser disposed over the cavity and transmitting the light beam. Preferably, the light diffuser comprises a holographic light diffuser. The plurality of LEDs disposed in the housing cavity preferably are comprised of a first set emitting light at a first color, such as green, and a second set of LEDs emitting light at a second color, such as yellow light. Advantageously, the green LEDs and the yellow LEDs can be alternatively driven to establish the desired light from a single LED cavity.

The mask is selectively positionable over the LED area array in at least one dimension, and preferably in two dimensions. The mask may comprise of a template having an opening permitting only a portion of the light to be transmitted therethrough. This template may be keyed with respect to the housing for accurate alignment of the mask opening with respect to the area array of LEDs thereunder. The template may be secured using a Velcro® material or the like.

The mask, in combination with the lens optical characteristics and orientation, determines the angle of the light emitted through the lens. The mask, in combination with the lens, also determines the shape of the emitted light beam. Preferably, the light beam is adjustable +/−20° with respect to normal from the LED in the first dimension, and +/−10° in the second dimension.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.

1

A and

FIG. 2A

is a front perspective view and rear perspective view, respectively, of a solid state light apparatus according to a first preferred embodiment of the present invention including an optical alignment eye piece;

FIG.

2

A and

FIG. 2B

is a front perspective view and a rear perspective view, respectively, of a second preferred embodiment having a solar louvered external air cooled heatsink;

FIG. 3

is a side sectional view of the apparatus shown in

FIG. 1

illustrating the electronic and optical assembly and lens system comprising an array of LEDs directly mounted to a heatsink, directing light through a diffuser and through a Fresnel lens;

FIG. 4

is a perspective view of the electronic and optical assembly comprising the LED array, lense holder, light diffuser, power supply, main motherboard and daughterboard;

FIG. 5

is a side view of the assembly of

FIG. 4

illustrating the array of LEDs being directly mounted to the heatsink, below respective lenses and disposed beneath a light diffuser, the heatsink for terminally dissipating generated heat;

FIG. 6

is a top view of the electronics assembly of

FIG. 4

;

FIG. 7

is a side view of the electronics assembly of

FIG. 4

;

FIG. 8

is a top view of the lens holder adapted to hold lenses for the array of LEDs;

FIG. 9

is a sectional view taken alone lines

9

—

9

in

FIG. 8

illustrating a shoulder and side wall adapted to securely receive a respective lens for a LED mounted thereunder;

FIG. 10

is a top view of the heatsink comprised of a thermally conductive material and adapted to securingly receive each LED, the LED holder of

FIG. 8

, as well as the other componentry;

FIG. 11

is a side view of the light diffuser depicting its radius of curvature;

FIG. 12

is a top view of the light diffuser of

FIG. 11

illustrating the mounting flanges thereof;

FIG. 13

is a top view of a Fresnel lens as shown in

FIG. 3

;

FIG. 14A

is a view of a remote monitor displaying an image generated by a video camera in the light apparatus to facilitate electronic alignment of the LED light beam;

FIG. 14B

is a perspective view of the lid of the apparatus shown in

FIG. 1

having a grid overlay for use with the optical alignment system;

FIG. 15

is a perspective view of the optical alignment system eye piece adapted to connect to the rear of the light unit shown in

FIG. 1

;

FIG. 16

is a schematic diagram of the control circuitry disposed on the daughterboard and incorporating various features of the invention including control logic, as well as light detectors for sensing ambient light and reflected generated light from the light diffuser used to determine and control the light output from the solid state light;

FIG. 17

is an algorithm depicting the sensing of ambient light and backscattered light to selectably provide a constant output of light;

FIGS.

18

A and

FIG. 18B

are side sectional views of an alternative preferred embodiment including a heatsink with recesses, with the LED's wired in parallel and series, respectively;

FIG. 19

is an algorithm depicting generating information indicative of the light operation, function and prediction of when the said state apparatus will fail or provide output below acceptable light output;

FIGS. 20 and 21

illustrate operating characteristics of the LEDs as a function of PWM duty cycles and temperature as a function of generated output light;

FIG. 22

is a block diagram of a modular light apparatus having selectively interchangeable devices that are field replaceable;

FIG. 23

is a perspective view of a light guide having a light channel for each LED to direct the respective LED light to the diffuser;

FIG. 24

shows a top view of

FIG. 23

of the light guide for use with the diffuser;

FIG. 25

shows a side sectional view taken along line

24

—

24

in

FIG. 3

illustrating a separate light guide cavity for each LED extending to the light diffuser;

FIG. 26

is a top view of an LED light source including a single reflector with an array of LEDs therein, the cavity which can be selectively masked through responsively determining the angle that light is ultimately transmitted from a lens disposed thereover;

FIG. 27

is a side sectional view taken along line

27

—

27

in

FIG. 26

;

FIG. 28

is a exploded side view of the housing cavity and a light diffuser/cover disposed thereover;

FIG. 29

is a top view of the light diffuser shown in

FIG. 28

;

FIG. 30

is a side sectional view taken along line

30

—

30

in

FIG. 29

;

FIG. 31

is a top view of a single cavity split-phase light source adapted for use at a pedestrian head; and

FIG. 32

depicts a single lens transmitting both light beams.

FIG. 33

depicts the operation of a pair of split-phase pedestrian head signals controlled to inform pedestrians at different locations of an intersection whether it is safe to walk.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to

FIG. 1A

, there is illustrated generally at

10

a front perspective view of a solid state lamp apparatus according to a first preferred embodiment of the present invention. Light apparatus

10

is seen to comprise a trapezoidal shaped housing

12

, preferably comprised of plastic formed by a plastic molding injection techniques, and having adapted to the front thereof a pivoting lid

14

. Lid

14

is seen to have a window

16

, as will be discussed shortly, permitting light generated from within housing

12

to be emitted as a light beam therethrough. Lid

14

is selectively and securable attached to housing

12

via a hinge assemble

17

and secured via latch

18

which is juxtaposed with respect to a housing latch

19

, as shown.

Referring now to FIG.

1

B and

FIG. 2B

, there is illustrated a second preferred embodiment of the present invention at

32

similar to apparatus

10

, whereby a housing

33

includes a solar louver

34

as shown in FIG.

2

B. The solar louver

34

is secured to housing

33

and disposed over a external heatsink

20

which shields the external heatsink

20

from solar radiation while permitting outside airflow across the heatsink

20

and under the shield

34

, thereby significantly improving cooling efficiency as will be discussed more shortly.

Referring to

FIG. 2A

, there is shown light apparatus

10

of

FIG. 1A

having a rear removable back member

20

comprised of thermally conductive material and forming a heatsink for radiating heat generated by the internal solid state light source, to be discussed shortly. Heatsink

20

is seen to have secured thereto a pair hinges

22

which are rotatably coupled to respective hinge members

23

which are securely attached and integral to the bottom of the housing

12

, as shown. Heatsink

20

is further seen to include a pair of opposing upper latches

24

selectively securable to respective opposing latches

25

forming an integral portion of and secured to housing

12

. By selectively disconnecting latches

24

from respective latches

25

, the entire rear heatsink

20

may be pivoted about members

23

to access the internal portion of housing

12

, as well as the light assembly secured to the front surface of heatsink

20

, as will be discussed shortly in regards to FIG.

3

.

Still referring to

FIG. 2A

, light apparatus

10

is further seen to include a rear eye piece

26

including a U-shaped bracket extending about heatsink

20

and secured to housing

12

by slidably locking into a pair of respective locking members

29

securely affixed to respective sidewalls of housing

12

. Eye piece

26

is also seen to have a cylindrical optical sight member

28

formed at a central portion of, and extending rearward from, housing

12

to permit a user to optically view through apparatus

10

via optically aligned window

16

to determine the direction a light beam, and each LED, is directed, as will be described in more detail with reference to FIG.

14

and FIG.

15

. Also shown is housing

12

having an upper opening

30

with a serrated collar centrally located within the top portion of housing

12

, and opposing opening

30

at the lower end thereof, as shown in FIG.

3

. Openings

30

facilitate securing apparatus

10

to a pair of vertical posts allowing rotation laterally thereabout.

Referring now to

FIG. 3

, there is shown a detailed cross sectional view taken along line

3

—

3

in

FIG. 1

, illustrating a solid state light assembly

40

secured to rear heatsink

20

in such an arrangement as to facilitate the transfer of heat generated by light assembly

40

to heatsink

20

for the dissipation of heat to the ambient via heatsink

20

.

Solid state light assembly

40

is seen to comprise an array of light emitting diodes (LEDs)

42

aligned in a matrix, preferably comprising an 8×8 array of LEDs each capable of generating a light output of 1-3 lumens. However, limitation to the number of LEDs or the light output of each is not to be inferred. Each LED

42

is directly bonded to heatsink

20

within a respective light reflector comprising a recess defined therein. Each LED

42

is hermetically sealed by a glass material sealingly diffused at a low temperature over the LED die

42

and the wire bond thereto, such as 8000 Angstroms of, SiO

2

or Si

3

N

4

material diffused using a semiconductor process. The technical advantages of this glass to metal hermetic seal over plastic/epoxy seals is significantly a longer LED life due to protecting the LED die from oxygen, humidity and other contaminants. If desired, for more light output, multiple LED dies

42

can be disposed in one reflector recess. Each LED

42

is directly secured to, and in thermal contact arrangement with, heatsink

20

, whereby each LED is able to thermally dissipate heat via the bottom surface of the LED. Interfaced between the planar rear surface of each LED

42

is a thin layer of heat conductive material

46

, such as a thin layer of epoxy or other suitable heat conductive material insuring that the entire rear surface of each LED

42

is in good thermal contact with rear heatsink

20

to efficiently thermally dissipate the heat generated by the LEDs. Each LED connected electrically in parallel has its cathode electrically coupled to the heatsink

20

, and its Anode coupled to drive circuitry disposed on daughterboard

60

. Alternatively, if each LED is electrically connected in series, the heatsink

20

preferably is comprised of an electrically non-conductive material such as ceramic.

Further shown in

FIG. 3

is a main circuit board

48

secured to the front surface of heatsink

20

, and having a central opening for allowing LED to pass generated light therethrough. LED holder

44

mates to the main circuit board

48

above and around the LED's

42

, and supports a lens

86

above each LED. Also shown is a light diffuser

50

secured above the LEDs

42

by a plurality of standoffs

52

, and having a rear curved surface

54

spaced from and disposed above the LED solid state light source

40

, as shown. Each lens

86

(

FIG. 9

) is adapted to ensure each LED

42

generates light which impinges the rear surface

54

having the same surface area. Specifically, the lenses

86

at the center of the LED array have smaller radius of curvature than the lenses

86

covering the peripheral LEDs

42

. The diffusing lenses

46

ensure each LED illuminates the same surface area of light diffuser

50

, thereby providing a homogeneous (uniform) light beam of constant intensity.

A daughter circuit board

60

is secured to one end of heatsink

20

and main circuit board

48

by a plurality of standoffs

62

, as shown. At the other end thereof is a power supply

70

secured to the main circuit board

48

and adapted to provide the required drive current and drive voltage to the LEDs

42

comprising solid state light source

40

, as well as electronic circuitry disposed on daughterboard

60

, as will be discussed shortly in regards to the schematic diagram shown in FIG.

16

. Light diffuser

50

uniformly diffuses light generated from LEDs

42

of solid state light source

40

to produce a homogeneous light beam directed toward window

16

.

Window

16

is seen to comprise a lens

70

, and a Fresnel lens

72

in direct contact with lens

70

and interposed between lens

70

and the interior of housing

12

and facing light diffuser

50

and solid state light source

40

. Lid

14

is seen to have a collar defining a shoulder

76

securely engaging and holding both of the round lens

70

and

72

, as shown, and transparent sheet

73

having defined thereon grid

74

as will be discussed further shortly. One of the lenses

70

or

72

are colored to produce a desired color used to control traffic including green, yellow, red, white and orange.

It has been found that with the external heatsink being exposed to the outside air the outside heatsink

20

cools the LED die temperature up to 50° C. over a device not having a external heatsink. This is especially advantageous when the sun setting to the west late in the afternoon such as at an elevation of 10° or less, when the solar radiation directed in to the lenses and LEDs significantly increasing the operating temperature of the LED die for westerly facing signals. The external heatsink

20

prevents extreme internal operating air and die temperatures and prevents thermal runaway of the electronics therein.

Referring now to

FIG. 4

, there is shown the electronic and optic assembly comprising of solid state light source

40

, light diffuser

50

, main circuit board

48

, daughter board

60

, and power supply

70

. As illustrated, the electronic circuitry on daughter board

60

is elevated above the main board

48

, whereby standoffs

62

are comprised of thermally nonconductive material.

Referring to

FIG. 5

, there is shown a side view of the assembly of

FIG. 4

illustrating the concave light diffuser

50

being axially centered and having a convex bottom surface disposed above the solid state LED array

40

. Diffuser

50

, in combination with the varying diameter lenses

86

, facilitates light generated from the area array of LEDs

42

to be uniformly disbursed and have uniform intensity and directed upwardly upon and across the convex bottom surface of the light diffuser

50

such that a homogenous light beam is generated toward the lens

70

and

72

, as shown in FIG.

3

. The lenses

86

proximate the center of the area array have a smaller radius of curvature than the peripheral lenses

86

which tend to be flatter. This lens arrangement provides that the LEDs

42

uniformly illuminate the curved diffuser

50

, even at the upwardly curved edges thereof. The outer lenses

86

, tend to columnate the light of the peripheral LEDs more than the central lenses

86

. Each LED illuminates an equal area of the diffuser.

Referring now to

FIG. 6

, there is shown a top view of the assembly shown in

FIG. 4

, whereby

FIG. 7

illustrates a side view of the same.

Referring now to

FIG. 8

, there is shown a top view of the lens holder

44

comprising a plurality of openings

80

each adapted to receive one of the LED lenses

86

hermetically sealed to and bonded thereover. Advantageously, the glass to metal hermetic seal has been found in this solid state light application to provide excellent thermal conductivity and hermetic sealing characteristics. Each opening

80

is shown to be defined in a tight pack arrangement about the plurality of LEDs

42

. As previously mentioned, the lenses

86

at the center of the array, shown at

81

, have a smaller curvature diameter than the lenses

86

over the perimeter LEDs

42

to increase light dispersion and ensure uniform light intensity impinging diffuser

50

.

Referring to

FIG. 9

, there is shown a cross section taken alone line

9

—

9

in

FIG. 8

illustrating each opening

80

having an annular shoulder

82

and a lateral sidewall

84

defined so that each cylindrical lens

86

is securely disposed within opening

80

above a respective LED

42

. Each LED

42

is preferably mounted to heatsink

20

using a thermally conductive adhesive material such as epoxy to ensure there is no air gaps between the LED

42

and the heatsink

20

. The present invention derives technical advantages by facilitating the efficient transfer of heat from LED

42

to the heatsink

20

.

Referring now to

FIG. 10

, there is shown a top view of the main circuit board

48

having a plurality of openings

90

facilitating the attachment of standoffs

62

securing the daughter board above an end region

92

. The power supply

48

is adapted to be secured above region

94

and secured via fasteners disposed through respective openings

96

at each corner thereof. Center region

98

is adapted to receive and have secured thereagainst in a thermal conductive relationship the LED holder

42

with the thermally conductive material

46

being disposed thereupon. The thermally conductive material preferably comprises of epoxy, having dimensions of, for instance, 0.05 inches. A large opening

99

facilitates the attachment of LED's

42

to the heatsink

20

, and such that light from the LEDs

42

is directed to the light diffuser

50

.

Referring now to

FIG. 11

, there is shown a side elevational view of diffuser

50

having a lower concave surface

54

, preferably having a radius A of about 2.4 inches, with the overall diameter B of the diffuser including a flange

55

being about 6 inches. The depth of the rear surface

52

is about 1.85 inches as shown as dimension C.

Referring to

FIG. 12

, there is shown a top view of the diffuser

50

including the flange

56

and a plurality of openings

58

in the flange

56

for facilitating the attachment of standoffs

52

to and between diffuser

50

and the heatsink

20

, shown in FIG.

4

.

Referring now to

FIG. 13

there is shown the Fresnel lens

72

, preferably having a diameter D of about 12.2 inches. However, limitation to this dimension is not to be inferred, but rather, is shown for purposes of the preferred embodiment of the present invention. The Fresnel lens

72

has a predetermined thickness, preferably in the range of about 1/16 inches. This lens is typically fabricated by being cut from a commercially available Fresnel lens.

Referring now back to FIG.

1

A and

FIG. 1B

, there is shown generally at

56

a video camera oriented to view forward of the front face of solid state lamp

10

and

30

, respectively. The view of this video camera

56

is precisionally aligned to view along and generally parallel to the central longitudinal axis shown at

58

that the beam of light generated by the internal LED array is oriented. Specifically, at large distances, such as greater than 20 feet, the video camera

56

generates an image having a center of the image generally aligned with the center of the light beam directed down the center axis

58

. This allows the field technician to remotely electronically align the orientation of the light beam referencing this video image.

For instance, in one preferred embodiment the control electronics

60

has software generating and overlaying a grid along with the video image for display at a remote display terminal, such as a LCD or CRT display shown at

59

in FIG.

14

A. This video image is transmitted electronically either by wire using a modem, or by wireless communication using a transmitter allowing the field technician on the ground to ascertain that portion of the road that is in the field of view of the generated light beam. By referencing this displayed image, the field technician can program which LEDs

42

should be electronically turned on, with the other LEDs

42

remaining off, such that the generated light beam will be focused by the associated optics including the Fresnel lens

72

, to the proper lane of traffic. Thus, on the ground, the field technician can electronically direct the generated light beam from the LED arrays, by referencing the video image, to the proper location on the ground without mechanical adjustment at the light source, such as by an operator situated in a DOT bucket. For instance, if it is intended that the objects viewable and associated with the upper four windows defined by the grid should be illuminated, such as those objects viewable through the windows labeled as W in

FIG. 14A

, the LEDs

42

associated with the respective windows “W” will be turned on, with the rest of the LEDs

46

associated with the other windows being turned off. Preferably, there is one LED

46

associated with each window defined by the grid. Alternatively, a transparent sheet

73

having a grid

74

defining windows

78

can be laid over the display surface of the remote monitor

59

whereby each window

78

corresponds with one LED. For instance, there may be 64 windows associated with the 64 LEDs of the LED array. Individual control of the respective LEDs is discussed hereafter in reference to FIG.

14

A. The video camera

56

, such as a CCD camera or a CMCS camera, is physically aligned alone the central axis

58

, such that at extended distances the viewing area of the camera

56

is generally along the axis

58

and thus is optically aligned with regards to the normal axis

58

for purposes of optical alignment.

Referring now to

FIG. 14B

, there is illustrated the lid

14

, the hinge members

17

, and the respective latches

18

. Holder

14

is seen to further have an annular flange member

70

defining a side wall about window

16

, as shown. Further shown the transparent sheet

73

and grid

74

comprising of thin line markings defined over openings

16

defining windows

78

. The sheet can be selectively placed over window

16

for alignment, and which is removable therefrom after alignment. Each window

78

is precisionally aligned with and corresponds to one sixty four (

64

) LEDs

42

. Indicia

79

is provided to label the windows

78

, with the column markings preferably being alphanumeric, and the columns being numeric. The windows

78

are viable through optical sight member

28

, via an opening in heatsink

20

. The objects viewed in each window

78

are illuminated substantially by the respective LED

42

, allowing a technician to precisionally orient the apparatus

10

so that the desired LEDs

42

are oriented to direct light along a desired path and be viewed in a desired traffic lane. The sight member

28

may be provided with cross hairs to provide increased resolution in combination with the grid

74

for alignment.

Moreover, electronic circuitry

100

on daughterboard

60

can drive only selected LEDs

42

or selected 4×4 portions of array

40

, such as a total of 16 LED's

42

being driven at any one time. Since different LED's have lenses

86

with different radius of curvature different thicknesses, or even comprised of different materials, the overall light beam can be electronically steered in about a 15° cone of light relative to a central axis defined by window

16

and normal to the array center axis.

For instance, driving the lower left 4×4 array of LEDs

42

, with the other LEDs off, in combination with the diffuser

50

and lens

70

and

72

, creates a light beam +7.5 degrees above a horizontal axis normal to the center of the 8×8 array of LEDs

42

, and +7.5 degrees right of a vertical axis. Likewise, driving the upper right 4×4 array of LEDs

42

would create a light beam +10 degrees off the horizontal axis and +7.5 degrees to the right of a normalized vertical axis and−7.5 degrees below a vertical axis. The radius of curvature of the center lenses

86

may be, for instance, half that of the peripheral lenses

86

. A beam steerable +/−7.5 degrees in 1-2 degree increments is selectable. This feature is particularly useful when masking the opening

16

, such as to create a turn arrow. This further reduces ghosting or roll-off, which is stray light being directed in an unintended direction and viewable from an unintended traffic lane.

The electronically controlled LED array provides several technical advantages including no light is blocked, but rather is electronically steered to control a beam direction. Low power LEDs are used, whereby the small number of the LEDs “on” (i.e. 4 of 64) consume a total power about 1-2 watts, as opposed to an incandescent prior art bulb consuming 150 watts or a flood 15 watt LED which are masked or lowered. The present invention reduces power and heat generated thereby.

Referring now to

FIG. 15

, there is shown a perspective view of the eye piece

26

as well as the optical sight member

28

, as shown in FIG.

1

. The center axis of optical sight member

28

is oriented along the center of the 8×8 LED array.

Referring now to

FIG. 16

, there is shown at

100

a schematic diagram of the circuitry controlling light apparatus

10

. Circuit

10

is formed on the daughter board

60

, and is electrically connected to the LED solid state light source

40

, and selectively drives each of the individual LEDs

42

comprising the array. Depicted in

FIG. 16

is a complex programmable logic device (CPLD) shown as U

1

. CPLD U

1

is preferably an off-the-shelf component such as provided by Maxim Corporation, however, limitation to this specific part is not to be inferred. For instance, discrete logic could be provided in place of CPLD U

1

to provide the functions as is described here, with it being understood that a CPLD is the preferred embodiment is of the present invention. CPLD U

1

has a plurality of interface pins, and this embodiment, shown to have a total of 144 connection pins. Each of these pin are numbered and shown to be connected to the respective circuitry as will now be described.

Shown generally at

102

is a clock circuit providing a clock signal on line

104

to pin

125

of the CPLD U

1

. Preferably, this clock signal is a square wave provided at a frequency of 32.768 KHz. Clock circuit

102

is seen to include a crystal oscillator

106

coupled to an operational amplifier U

5

and includes associated trim components including capacitors and resistors, and is seen to be connected to a first power supply having a voltage of about 3.3 volts.

Still referring to

FIG. 16

, there is shown at

110

a power up clear circuit comprised of an operational amplifier shown at U

6

preferably having the non-inverting output coupled to pin

127

of CPLD U

1

. The inverting input is seen to be coupled between a pair of resistors providing a voltage divide circuit, providing approximately a 2.425 volt reference signal based on a power supply of 4.85 volts being provided to the positive rail of the voltage divide network. The inverting input is preferably coupled to the 4.85 voltage reference via a current limiting resistor, as shown.

As shown at

112

, an operational amplifier U

9

is shown to have its non-inverting output connected to pin

109

of CPLD U

1

. Operational amplifier U

9

provides a power down function.

Referring now to circuit

120

, there is shown a light intensity detection circuit detecting ambient light intensity and comprising of a photodiode identified as PD

1

. An operational amplifier depicted as U

7

is seen to have its non-inverting input coupled to input pin

99

of CPLD U

1

. The non-inverting input of amplifier U

7

is connected to the anode of photodiode PD

1

, which photodiode has its cathode connected via a capacitor to the second power supply having a voltage of about 4.85 volts. The non-inverting input of amplifier U

7

is also connected via a diode Q

1

, depicted as a transistor with its emitter tied to its base and provided with a current limiting resistor. The inverting input of amplifier U

7

is connected via a resistor to input

108

of CPLD U

1

.

Shown at

122

is a similar light detection circuit detecting the intensity of backscattered light from Fresnel lens

72

as shown at

124

in

FIG. 3

, and based around a second photodiode PD

2

, including an amplifier U

10

and a diode Q

2

. The non-inverting output of amplifier U

10

, forming a buffer, is connected to pin

82

of CPLD U

1

.

An LED drive connector is shown at

130

serially interfaces LED drive signal data to drive circuitry of the LEDs

42

. (Inventors please describe the additional drive circuit schematic).

Shown at

140

is another connector adapted to interface control signals from CPLD U

1

to an initiation control circuit for the LED's.

Each of the LEDs

42

is individually controlled by CPLD U

1

whereby the intensity of each LED

42

is controlled by the CPLD U

1

selectively controlling a drive current thereto, a drive voltage, or adjusting a duty cycle of a pulse width modulation (PWM) drive signal, and as a function of sensed optical feedback signals derived from the photodiodes as will be described shortly here, in reference to FIG.

17

.

Referring to

FIG. 17

in view of

FIG. 3

, there is illustrated how light generated by solid state LED array

40

is diffused by diffuser

50

, and a small portion

124

of which is back-scattered by the inner surface of Fresnel lens

72

back toward the surface of daughter board

60

. The back-scattered diffused light

124

is sensed by photodiodes PD

2

, shown in FIG.

16

. The intensity of this back-scattered light

124

is measured by circuit

122

and provided to CPLD U

1

. CPLD U

1

measures the intensity of the ambient light via circuit

120

using photodiode PD

1

. The light generated by LED's

42

is preferably distinguished by CPLD U

1

by strobing the LEDs

42

using pulse width modulation (PWM) to discern ambient light (not pulsed) from the light generated by LEDs

42

.

CPLD U

1

individually controls the drive current, drive voltage, or PWM duty cycle to each of the respective LEDs

42

as a function of the light detected by circuits

120

and

122

. For instance, it is expected that between 3 and 4% of the light generated by LED array

40

will back-scatter back from the Fresnel lens

72

toward to the circuitry

100

disposed on daughter board

60

for detection. By normalizing the expected reflected light to be detected by photodiodes PD

2

in circuit

122

, for a given intensity of light to be emitted by LED array

40

through window

16

of lid

14

, optical feedback is used to ensure an appropriate light output, and a constant light output from apparatus

10

.

For instance, if the sensed back-scattered light, depicted as rays

124

in

FIG. 3

, is detected by photodiodes PD

2

to fall about 2.5% from the normalized expected light to be sensed by photodiodes PD

2

, such as due to age of the LEDs

42

, CPLD U

1

responsively increases the drive current to the LEDs a predicted percentage, until the back-scattered light as detected by photodiodes PD

2

is detected to be the normalized sensed light intensity. Thus, as the light output of LEDs

42

degrade over time, which is typical with LEDs, circuit

100

compensates for such degradation of light output, as well as for the failure of any individual LED to ensure that light generated by array

40

and transmitted through window

16

meets Department of Transportation (DOT) standards, such as a 44 point test. This optical feedback compensation technique is also advantageous to compensate for the temporary light output reduction when LEDs become heated, such as during day operation, known as the recoverable light, which recoverable light also varies over temperatures as well. Permanent light loss is over time of operation due to degradation of the chemical composition of the LED semiconductor material.

Preferably, each of the LEDs is driven by a pulse width modulated (PWM) drive signal, providing current during a predetermined portion of the duty cycle, such as for instance, 50%. As the LEDs age and decrease in light output intensity, and also during a day due to daily temperature variations, the duty cycle may be responsively, slowly and continuously increased or adjusted such that the duty cycle is appropriate until the intensity of detected light by photodiodes PD

2

is detected to be the normalized detected light. When the light sensed by photodiodes PD

2

are determined by controller

60

to fall below a predetermined threshold indicative of the overall light output being below DOT standards, a notification signal is generated by the CPLD U

1

which may be electronically generated and transmitted by an RF modem, for instance, to a remote operator allowing the dispatch of service personnel to service the light. Alternatively, the apparatus

10

can responsively be shut down entirely.

Referring now to FIG.

18

A and

FIG. 18B

, there is shown an alternative preferred embodiment of the present invention including a heatsink

200

machined or stamped to have an array of reflectors

202

. Each recess

202

is defined by outwardly tapered sidewalls

204

and a base surface

208

, each recess

202

having mounted thereon a respective LED

42

. A lens array having a separate lens

210

for each LED

42

is secured to the heatsink

200

over each recess

202

, eliminating the need for a lens holder. The tapered sidewalls

206

serve as light reflectors to direct generated light through the respective lens

210

at an appropriate angle to direct the associated light to the diffuser

50

having the same surface area of illumination for each LED

42

. In one embodiment, as shown in

FIG. 18A

, LEDs

42

are electrically connected in parallel. The cathode of each LED

42

is electrically coupled to the electrically conductive heatsink

200

, with a respective lead

212

from the anode being coupled to drive circuitry

216

disposed as a thin film PCB

45

adhered to the surface of the heatsink

200

, or defined on the daughterboard

60

as desired. Alternatively, as shown in

FIG. 18B

, each of the LED's may be electrically connected in series, such as in groups of three, and disposed on an electrically non-conductive thermally conductive material

43

such as ceramic, diamond, SiN or other suitable materials. In a further embodiment, the electrically non-conductive thermally conductive material may be formed in a single process by using a semiconductor process, such as diffusing a thin layer of material in a vacuum chamber, such as 8000 Angstroms of SiN, which a further step of defining electrically conductive circuit traces

45

on this thin layer.

FIG. 19

shows an algorithm controller

60

applies for predicting when the solid state light apparatus will fail, and when the solid state light apparatus will produce a beam of light having an intensity below a predetermined minimum intensity such as that established by the DOT. Referring to the graphs in

FIG. 20 and 21

, the known operating characteristics of the particular LEDs produced by the LED manufacture are illustrated and stored in memory, allowing the controller

60

to predict when the LED is about the fail. Knowing the LED drive current operating temperature, and total time the LED as been on, the controller

60

determines which operating curve in FIG.

20

and

FIG. 21

applies to the current operating conditions, and determines the time until the LED will degrade to a performance level below spec, i.e. below DOT minimum intensity requirements.

FIG. 22

depicts a block diagram of the modular solid state traffic light device. The modular field-replaceable devices are each adapted to selectively interface with the control logic daughterboard

60

via a suitable mating connector set. Each of these modular field replacable devices

216

are preferably embodied as a separate card, with possibly one or more feature on a single field replacable card, adapted to attach to daughterboard

60

by sliding into or bolting to the daughterboard

60

. The devices can be selected from, alone or in combination with, a pre-emption device, a chemical sniffer, a video loop detector, an adaptive control device, a red light running (RLR) device, and an in-car telematic device, infrared sensors to sense people and vehicles under fog, rain, smog and other adverse visual conditions, automobile emission monitoring, various communication links, electronically steerable beam, exhaust emission violations detection, power supply predictive failure analysis, or other suitable traffic devices.

The solid state light apparatus

10

of the present invention has numerous technical advantages, including the ability to sink heat generated from the LED array to thereby reduce the operating temperature of the LEDs and increase the useful life thereof. Moreover, the control circuitry driving the LEDs includes optical feedback for detecting a portion of the back-scattered light from the LED array, as well as the intensity of the ambient light, facilitating controlling the individual drive currents, drive voltages, or increasing the duty cycles of the drive voltage, such that the overall light intensity emitted by the LED array

40

is constant, and meets DOT requirements. The apparatus is modular in that individual sections can be replaced at a modular level as upgrades become available, and to facilitate easy repair. With regards to circuitry

100

, CPLD U

1

is securable within a respective socket, and can be replaced or reprogrammed as improvements to the logic become available. Other advantages include programming CPLD U

1

such that each of the LEDs

42

comprising array

40

can have different drive currents or drive voltages to provide an overall beam of light having beam characteristics with predetermined and preferably parameters. For instance, the beam can be selectively directed into two directions by driving only portions of the LED array in combination with lens

70

and

72

. One portion of the beam may be selected to be more intense than other portions of the beam, and selectively directed off axis from a central axis of the LED array

40

using the optics and the electronic beam steering driving arrangement.

Referring now to

FIG. 23

, there is shown at

220

a light guide device having a concave upper surface and a plurality of vertical light guides shown at

222

. One light guide

222

having a light reflective inner surface is provided for and positioned over each LED

42

, which light guide

222

upwardly directs the light generated by the respective LED

42

to impinge the bottom convex surface of the concave diffuser

54

. The light guides

222

taper outwardly at a top end thereof, as shown in FIG.

24

and

FIG. 25

, such that the area at the top of each light guide

222

is identical. Thus, each LED

42

illuminates an equal surface area of the light diffuser

54

, thereby providing a uniform intensity light beam from light diffuser

54

. A thin membrane

224

defines the light guide, like a honeycomb, and tapers outwardly to a point edge at the top of the device

220

. These point edges are separated by a small vertical distance D shown in

FIG. 25

, such as 1 mm, from the above diffuser

54

to ensure uniform lighting at the transition edges of the light guides

222

while preventing bleeding of light laterally between guides, and to prevent light roll-off by generating a homogeneous beam of light. Vertical recesses

226

permit standoffs

52

extending along the sides of device

220

(see

FIG. 3

) to support the peripheral edge of the diffuser

54

. The lateral light guides are narrower than the central light guides due to the upward curvature of the diffuser edges.

Referring now to

FIG. 26

, there is shown generally at

300

another preferred embodiment of the present invention including a single cavity LED light apparatus having a single reflector, shown as a trough, the LED area array being covered with a light diffuser, as shown in FIG.

28

. The single cavity LED apparatus is selectively masked to establish a desired beam angle and shape emitted by the Fresnel lens, as shown in FIG.

28

.

A rectangular housing member shown at

302

defines a central rectangular cavity

304

with an array of LEDs

46

disposed therein. As shown, the LEDs

46

are disposed in a 4×8 area array, each LED

46

facing upwardly from a heatsink, as discussed in other embodiments, and each LED

46

preferably comprising an LED die such as a vertical cavity surface emitting laser (VCSEL). As shown in

FIG. 27

, the thickness of the housing

302

is approximately 1 inch, having a length of about 2.5 inches and a width of about 3 inches. The dimensions of the cavity

304

are approximately 1.1 inches in width, and 2.3 inches in length. Also shown in

FIG. 26

is a pair of opposing key slots

310

which facilitate a vertical light separation member to be vertically inserted therein to separate the upper portion of the LED array from the lower portion of the LED array.

Preferably, the LEDs

46

are comprised of two or more different colors, a plurality of one color forming a first set, such as green LEDs generating green light, and a plurality of another LED color, such as yellow LEDs generating yellow LED light, these colored LEDs being mixed throughout the array. Other colors are possible, such as red and amber LEDS. The plurality of LEDs

46

provide for redundancy, and the difference in colors provide the option to generate more than one color of light from the single LED light apparatus

300

.

Referring to

FIG. 28

, there is seen that the cover

312

comprising a holographic diffuser is secured to the top surface of the housing

302

. Referring to

FIG. 29

, there is seen the diffuser

312

has a window

314

comprised of a holographic material aligned with the opening

304

of the housing member

302

. That is, the profile of the window

314

conforms to the profile of the window

304

of the underlying housing member

302

.

Still referring to

FIG. 29

, there is shown at

320

a mask which is adapted to be selectively adhered to the surface of the cover

312

to selectively block a portion of window

314

, such as using Velcro® material. By selectively blocking a portion of window

314

, the mask restricts and blocks light from the associated underlying LEDs

46

, thereby allowing light from the unmasked LEDs

46

to be transmitted through the unmasked holographic diffuser material, and ultimately through the Fresnel lens shown in the other Figures. Since the LEDs

46

that are directing light through the lens are positioned below a center axis of the Fresnel lens, the light beam will be transmitted through the lens at an angle steerable upwardly from the lens center with respect to a central normal axis to the Fresnel lens.

For instance, by blocking the upper two rows of LEDs

46

as shown in

FIG. 26

, only the lower two rows of LEDs

46

will generate light that is ultimately communicated through the Fresnel lens. In this embodiment, the light beam generated through the lens will be directed roughly 10° from the center axis of the LED and upwardly. This is due to the combination of the orientation of the effective LEDs with respect to the lens, and the fact that the lens is a Fresnel lens.

Alternatively, if, say, only the two left columns of the LEDs

46

are unblocked by mask

320

as shown in phantom lines at

322

, the light beam generated through the lens is directed at an angle at approximately 20° to the right with respect to normal of the lens. Therefore, using the mask

320

, the angle of light generated through the lens of the light apparatus can be adjusted roughly +/−10° in one direction, and +/−20° in a second dimension. This allows for the selective mechanical steering of the light beam generated by the solid state LED array to custom define the angle at which the homogenous light generated by the LED array is directed. This allows for the light to be focused toward the appropriate lane of traffic to be controlled.

It is further noted that the selective masking of the LEDs also responsively shapes the beam of the light being transmitted through the lens. For instance, a larger beam is generated by an unmasked LED array, and a narrower beam of light is generated by a substantially masked LED array. As shown in

FIG. 29

, if the upper portion of the LED array is masked, the beam will have a narrow and long beam extending laterally, and conversely, if the left half of the LED array is masked, the beam will be substantially square and uniform in both the vertical and lateral direction. The inner walls of opening

304

are preferably coated with a light reflective material to facilitate that all light generated from the LEDs

46

be directed upwardly through the light diffuser

312

.

Referring now to

FIG. 31

, there is illustrated another advantageous use of the light apparatus

300

shown in

FIG. 26

comprising a split-phase pedestrian head. As shown in

FIG. 31

, light apparatus

300

is provided with a rectangular light separator

330

vertically disposed within the respective slots

310

, thereby physically separating the light generated by the upper row of LEDs

46

from the light generated by the lower row of LEDs

46

, depicted as an upper LED section

332

and in lower LED section

334

. Due to the optics, namely, the fact that the Fresnel lens is disposed over the apparatus

300

, as graphically depicted in

FIG. 32

, when the upper two rows of LEDs

46

are illuminated, a light beam directed downwardly at about 10° with respect to normal is generated as shown at

340

. Conversely, when the two lower rows of LEDs

46

are illuminated, with the upper two rows remaining off, the generated light beam is directed at a roughly 10° above the normal of the lens, as illustrated as

342

.

With the novel light apparatus

300

, a novel control algorithm of the same provides a split-phase light apparatus that finds one suitable use as a pair of split-phase pedestrian head signals. As depicted in

FIG. 33

, a pedestrian “P” at an opposing side of the street in position “A” from the pair of split-phase pedestrian heads can see light generated by the lower two rows of LEDs of the respective pedestrian heads. However, the pedestrian in position A cannot see light generated by the upper two rows of LEDs of the respective pedestrian heads.

Now referring to the pedestrian P at position “B”, namely, at a median of a lane of traffic, this pedestrian can see the light beam generated by the upper rows of LEDs

46

of each pedestrian heads, but not the light from the lower two rows of LEDs of the pedestrian heads which are still only visible by the pedestrian at position A.

The present invention finds technical advantages whereby a pair of split-phase pedestrian heads

300

, one stacked on top of the other as shown, can be used with the upper head

300

having a light screen shaped as a “stop hand” symbol

350

, and the lower head

300

may be screened with a “walk” symbol

352

. In a operational first state, i.e. when an associated traffic signal turns green, all LED rows of the lower walk signal

300

are illuminated such that the walk symbol

300

is illuminated and visible by pedestrian at both position A and at position B. However, at a second state in the cycle, only the upper two rows of the LEDs of lower lamp

300

are illuminated, thus, the illuminated walk symbol is viewable only by the pedestrian at position B due to the 10° beamwidth, and not by pedestrian at position A. Simultaneously, the upper “don't walk” pedestrian head

300

will have its lower two LED rows illuminated such that the “don't walk” signal is viewable by the pedestrian at position A due to the 10° beamwidth, but not by the pedestrian at position B who still only sees the illuminated “walk” signal. At a third state of the cycle, namely, when the associated traffic signal is about to turn yellow, all LED rows of the upper head

300

are illuminated such that the “don't walk” signal is viewable by a pedestrian at both position A and position B, and all rows of the LEDs of the lower head

300

are off.

The present invention helps overcome the confusion and uncertainty of a pedestrian attempting to cross an associated traffic way, allowing the pedestrian to ascertain whether or not there is sufficient time to cross the traffic lane. The control circuitry selectively drives the rows of LEDs in each of the upper “don't walk” and lower “walk” pedestrian heads

300

such that a pedestrian can better ascertain the instructions as whether or not to cross the street, or to continue crossing the street once half way there across such as shown in position B. As illustrated, both the upper and lower ped heads

300

have a maximum viewing angle of 20°, and a viewing angle of only 10° when just either the lower two rows or the upper two rows of LEDs are illuminated. Again, the lower 10° beam is viewable when the associated upper two rows of LEDs are illuminated, and conversely, the upper 10° beam is viewable when the associated two lower rows of LEDs are illuminated. The entire 20° beam is generated when all associated four rows of LEDs of the respective ped head

300

are illuminated.

Referring back to

FIG. 31

, the divider

330

separates light generated by the upper two rows and the lower two rows of LEDs

46

from mixing with the other, thereby further achieving directionality of the ultimate light beam generated by the ped head

300

towards the pedestrian. This divider

330

is not noticeable by the pedestrian when all rows are illuminated, but when only the upper or lower two LED rows are illuminated, the 10° beam directionality of the generated light is further controlled to avoid bleeding and provided a sharper roll-off of the light so that the pedestrian at the light in position B will not see both a walk signal and a stop hand signal.

A three cycle methodology is provided whereby at first stage of the cycle all LED rows of the lower “walk” ped head

300

are illuminated such that the walk symbol is seen by the pedestrian at both position A and at position B.

At a second stage of the cycle, the upper two LED rows of the walk ped head

300

are illuminated such that the walk symbol is only viewable by a pedestrian at position B, and whereby the lower two LED rows of the upper “stop hand” ped head

300

are illuminated such that the stop hand symbol is only viewable by the pedestrian at position A, but not by the pedestrian at position B.

At the third stage of the cycle, all LED rows of the lower “walk” ped head

300

are off, and all rows of the LEDs of the upper “stop hand” ped head

300

are illuminated such that the “stop hand” symbol is viewable by pedestrians at both positions A and B.

While the invention has been described in conjunction with preferred embodiments, it should be understood that modifications will become apparent to those of ordinary skill in the art and that such modifications are therein to be included within the scope of the invention and the following claims.

Number	Name	Date	Kind
5056039	Caulfield	Oct 1991	A
5309277	Deck	May 1994	A
5333071	Ishikawa et al	Jul 1994	A
5640792	Smith et al.	Jun 1997	A
6135604	Lin	Oct 2000	A

LED based trough designed mechanically steerable beam traffic signal

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Term Extension

Abstract

Description

Claims

US Referenced Citations (5)