IMPROVED LAMP COLOR TEMPERATURE STABILITY IN AN AUTOMATED LUMINAIRE

Abstract

Described is dynamic control of the temperature of the envelope of an HID lamp in order to stabilize the output color temperature of the lamp. As the lamp power is changed, or environmental factors alter the lamp envelope temperature, the system senses these changes and adjusts the lamp cooling systems so as to move the lamp envelope temperature back to the desired point.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to the control of the color temperature of a lamp, and more specifically to the color temperature of a high intensity discharge lamp as utilized in an automated luminaire.

BACKGROUND

Luminaires with automated and remotely controllable functionality are well known in the entertainment and architectural lighting markets. Such products are commonly used in theatres, television studios, concerts, theme parks, night clubs and other venues. A typical product will commonly provide control over the pan and tilt functions of the luminaire allowing the operator to control the direction the luminaire is pointing and thus the position of the light beam on the stage or in the studio. Typically this position control is done via control of the luminaire's position in two orthogonal rotational axes usually referred to as pan and tilt. Many products provide control over other parameters such as the intensity, color, focus, beam size, beam shape and beam pattern. FIG. 1 illustrates a typical multiparameter automated luminaire system 10. These systems typically include a plurality of multiparameter automated luminaires 12 which typically each contain on-board a light source (not shown), light modulation devices, electric motors coupled to mechanical drives systems and control electronics (not shown). In addition to being connected to mains power either directly or through a power distribution system (not shown), each luminaire is connected in series or in parallel to data link 14 to one or more control desks 15. An operator typically controls the luminaire system 10 through the control desk 15.

To achieve the high brightness needed for such systems it is common to utilize High Intensity Discharge lamps (HID). Short and medium arc HID lamps produce light from a plasma cloud produced by an electrical arc that is maintained between two adjacent electrodes within a sealed quartz envelope. FIG. 2 shows an example 30 of an HID lamp that may be used. Electrodes 32 and 33 are enclosed within sealed quartz envelope 38 and connected by lead wires 35 to a base 36 and electrical connections 37. The HID lamps used in entertainment lighting luminaires often use very small arc gaps 34 between the two electrodes, of the order of 1 to 5 mm, to provide a low etendue light source that facilitates the design of a high quality optical system for projecting images and colors. The spectrum of light emitted by the lamp is produced by the ionization and emission of a mix of rare earths and gases that are contained within the envelope 38. The emission spectra of each of these components, when heated to the plasma temperatures of the arc, combine to produce an overall emission spectrum for the lamp. The lamp manufacturer carefully selects the mix of constituents for the lamp fill in order to produce a white light output with a spectrum that approximates to that of a black body emitter at the desired color temperature. For example, it is common to manufacture HID lamps with a target color temperature of 5600 K, or daylight. It is also common to produce lamps with target color temperatures of 3200 K, 7000 K, 10000 K and other white points as commonly used in the entertainment lighting business for television cameras, film cameras or a live audience.

A significant problem with such lamps is maintaining the stability of the desired target color temperature. Small changes in the arc gap, as the electrodes burn away, and fluctuations in the temperature of the lamp envelope can make significant changes to the precise mix of constituents that are emitting spectra to the combined spectrum. For example, as the temperature drops within the envelope then some constituents that emit specific wavelengths of light may drop out of the ionization cloud, or alter their output, thus affecting the resultant output spectrum and thus the output color temperature. Lamp manufacturers may attempt to mitigate this variability by enclosing the inner quartz envelope 38 within a second outer envelope (not shown) to provide rudimentary temperature control. However, such designs are still not stable and the color temperature may vary significantly.

It is also common to desire to change the power consumed by the lamp, in order to control its brightness. Unfortunately any change in lamp power also affects the operating temperature of the lamp that, in turn, will affect the output color temperature. Prior art systems have utilized fan cooling systems to attempt to stabilize the lamp temperature, but these have been ineffective and slow to operate, allowing large changes in the lamp output color temperature that were visible to the audience.

It would be advantageous to provide a system that was capable of providing continuous and dynamic control of the temperature of the envelope of an HID lamp in order to stabilize the output color temperature of the lamp.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein:

FIG. 1 illustrates a typical prior art automated lighting system;

FIG. 2 illustrates a typical HID lamp; and;

FIG. 3 illustrates an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are illustrated in the FIGUREs, like numerals being used to refer to like and corresponding parts of the various drawings.

The present invention generally relates to the control of the color temperature of a lamp, and more specifically to the color temperature of a high intensity discharge lamp as utilized in an automated luminaire.

In one embodiment the present invention utilizes a tightly temperature controlled enclosure 40 for the HID lamp in order to maintain the lamp envelope temperature within close tolerances and thus maintain the color temperature of the light output from the lamp within close tolerances.

FIG. 3 illustrates one embodiment of the invention. High Intensity Discharge (HID) lamp 30 comprising electrodes 32 and 33 that are enclosed within sealed quartz envelope 38 and connected by lead wires 35 to a base 36. Base 36 may connect to lamp connector 44 from which electrical connections may be made to the control gear (not shown). In operation an electrical arc is formed across arc gap 34 creating a localized region containing high temperature plasma. This plasma excites the mix of rare earths and gases that are contained within envelope 38 such that a distinctive light spectrum is emitted. The constituent spectra forming the light output spectrum are sensitive to the temperature of the envelope 38. Lamp 30 is contained within enclosure 40 providing a controlled environment. Air may enter enclosure 40 through controllable fan or blower 42b and may exit the enclosure through controllable fan or blower 42a. Light from lamp 30 may be directed and controlled by reflector 41. One face of the enclosure 46 may be a window manufactured of a transparent material for the light from lamp 30 and reflector 41 to exit. Transparent window 46 may be planar, curved, faceted or any shape as known in the art. Transparent window 46 may be glass, quartz or other transparent material. Transparent window 46 may have coatings including but not limited to, dichroic hot mirror, colored dichroic, heat resistant coatings.

Enclosure 40 may further comprise a plurality of temperature sensors; 48a, 48b, 48c, 48d, and 48e. These temperature sensors are configured to read the temperature of critical points of the lamp, its enclosure, and the exiting and entering air. For example, temperature sensor 48a and 48c may measure the temperature at different points in enclosure 40. Temperature sensor 48e may measure the temperature of lamp base 36 or the lamp pinches. Temperature sensor 48b may measure the temperature of incoming air through controllable fan 42b, and temperature sensor 42a may measure the temperature of exiting air through controllable fan 42a. Additionally remote temperature sensors, such as 48f, may be utilized elsewhere in the luminaire as desired.

In operation all temperature sensors 48a-48f, controllable fans 42a and 42b are connected to and controlled by a central controller 50. In manufacturing and testing controller 50 may be configured with knowledge of the configuration of enclosure 40, lamp 30, and the positions and parameters of temperature sensors 48a-48f and fans 42a and 42b. This knowledge includes the time constants of the various connected items, and the amount of time it takes to heat or cool lamp envelope 38 and lamp pinches as a function of lamp power, temperatures, and fan speeds. Algorithms in controller 50 may be configured so as to operate temperature control of enclosure 40, and thus lamp envelope 38, as a parameterized closed loop system such that all temperatures are monitored and fan speeds raised and lowered as needed to keep the temperature of lamp envelope 38 at a constant point.

The control system has access to a lighting plan that includes the planned lamp power when the lamp is being dimmed or undergoing other activities that may affect envelope temperature as a function of time, such that it can pro-actively adjust fan speeds to allow for a predicted temperature change that will occur from any particular change in lamp power. For example, a particular lamp may be operated at 1700W, 1500W, 1200W, 900W or other wattage while maintaining a constant lamp temperature, and thus a constant light output color temperature. In other embodiments maintaining color temperature constant may require variation in the lamp temperature.

In a further embodiment the lamp may be configures to run at an extremely low power when the unit is shuttered or in blackout with no light emerging. In prior art products this led to a significantly lowered lamp temperature that, in turn, produced a much higher output color temperature. When the lamp was opened up from blackout and raised back to full power, this high color temperature was noticeable as was the change in color temperature as the lamp warmed up and was objectionable to the viewer or television camera. However, with the system of the invention, controller 50 may recognize the blackout condition and automatically lower fan speeds sop that the lamp temperature remains at the correct level. Then, when the lamp is opened up from blackout the color temperature of the output light will be correct and stable.

In further embodiments of the invention different numbers and positions of temperature sensors are used.

A particular style of single ended HID lamp is illustrated in FIG. 3. The invention is not so limited and any style of lamp, single ended, double ended, integral reflector, and other lamp styles as known in the art could be used in an embodiment of the invention.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this invention, will appreciate that other embodiments may be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

The invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as described by the appended claims

Claims

1. An automated luminaire comprising: a light source that generates different color temperature light based on variance in its operating conditions;an enclosure for the light source with fan(s) which gate the flow of air into and out of the enclosure;temperature sensor(s) which monitor temperatures that effect the temperature inside the enclosure;controller that monitors power to the lamp as a function of time historically and prospectively based on a preprogrammed light show and operating temperature and controls airflow to maintain operating temperature given power applied to the lamp to optimize a constant lamp output color temperature as a function of time.

2. An automated luminaire comprising: a light source that generates different color temperature light based on variance in its operating conditions;an enclosure for the light source with fan(s) which gate the flow of air into and out of the enclosure;temperature sensor(s) which monitor temperatures that effect the temperature inside the enclosure;controller that monitors power to the lamp and operating temperature and controls airflow to maintain operating temperature given power applied to the lamp so that the lamp output color temperature is maintained as constant.

3. The luminaire of claim 2 where the temperature in the enclosure is maintained as constant independent of power applied.

4. The luminaire of claim 2 where the target temperature in the enclosure depends on the driving power applied to the lamp.

5. The luminaire of claim 2 where the temperatures monitored includes the temperature in the enclosure, and the input air temperature

6. The luminaire of claim 2 where the temperatures monitored includes the temperature in the enclosure, and the input air temperature and the output air temperature.

7. The luminaire claim 2 where the temperatures monitored includes the temperature in the enclosure, and the input air temperature and the output air temperature the ambient air temperature.

8. The luminaire claim 2 where the temperatures monitored includes the temperature at a plurality of locations in the enclosure.

9. The luminaire claim 2 where the temperatures monitored includes the temperature at the lamp base.