Patent Application
20160128155
The present disclosure is related to an LED lighting system and method with incandescent style dimming characteristics.
Incandescent light sources have been used for many years in lighting fixtures. An incandescent light source, such as an incandescent light bulb, includes a filament, which when heated emits light. The filament in the incandescent bulb typically emits a light with a color temperature of about 3000 Kelvin (K) at full brightness, which is considered a “white” color. As the incandescent light source is dimmed by decreasing current, the filament emits a light that shifts away from a cooler color temperature, e.g., “white”, toward a warmer color temperature, such as yellow, orange, and then red. The color temperature change of an incandescent light bulb generally follow the color change of a cooling black body, i.e., a black body locus. An example of a dimming color curve for an incandescent light source, such as a halogen light source, is shown in
Light Emitting Diodes (LEDs) have begun to replace traditional incandescent light sources in lighting fixtures. LEDs are efficient and reliable, and are able to emit a bright white light. Blue LEDs with a phosphor coating are typically used to produce white light. However, unlike traditional incandescent bulbs, the color temperature of an LED does not significantly change when the LED is dimmed. For example, when dimmed, the white light from an LED does not appear red but instead can become even more bluish.
One way to simulate the dimming characteristic of an incandescent lamp with an LED light source is to optically mix white LEDs with amber (e.g., yellow/orange) LEDs, and to control their currents in such a manner that the mixed color light from the LED combination changes from white tight to a more amber-yellow-white color with dimming. Traditionally, LED systems performing mixing of colored LEDs use individual drivers to control each colored LED separately, or use a single driver designed to have two or more separate output channels, where each output channel is controlled individually within the driver. An example of such a circuit is described in U.S. Pat. No. 7,288,902 to Melanson.
A dimmable LED lighting system and method are provided in which three or more LED light sources with different spectral power distribution (SPD) curves are selected to model a dimming color curve, such as for an incandescent light source (e.g., a black body locus curve). For example, the dimmable LED lighting system includes first, second and third types of LED light sources and an LED driver to selectively supply current to each of the LED light sources on first, second and third channels, respectively. The three types of LED light sources are selected according to their SPD curves, which together model a dimming color curve that is characteristic of an incandescent light source when the LED light sources are driven by the LED driver at predefined power ratios that correspond to dimming levels over a dimming region of the dimming color curve. The different types of LED light sources may be selected according to maximum (e.g., peak) and minimum (e.g., valley) profiles of their SPD curves, e.g., spectral power versus wavelength.
Accordingly, a dimmable LED lighting system can be designed and manufactured using a combination of three or more types of LED light sources with selected SPD curves to provide a custom dimming color curve that can offer a high general color rendering index (CRI) of Ra over a dimming region. For example, the dimmable LED lighting system can be configured with an Ra greater than 80. Moreover, the dimmable lighting system can be configured with an Ra greater than 90 over the dimming region with one of the three types of LED light source on one channel having an Ra greater than 90 and the other two types of LED light sources on the other channels having an Ra less than 90 (e.g., 80<Ra<90). The dimmable lighting system can also be configured to have a value of R9 greater than 50 over a dimming region even though the different types of LED light sources have a value of R9 less than 50.
The present disclosure provides a flexible approach to designing and implementing dimmable LED lighting systems with customized color dimming curves that model, for example, those of an incandescent light source, or in other words, with incandescent style dimming. A dimmable LED lighting system with incandescent style dimming can be designed with three or more different types of LED light sources, which are selected according to their spectral power distribution (SPD) curves and driven at predefined power ratios therebetween over a dimming region of the LED lighting system. Through the selection of different types of LED light sources according to their SPD curves, the dimmable LED lighting system can also be configured to achieve higher color rendering index (CRI) with proper color mixing throughout the dimming region.
Prior to discussing the exemplary embodiments of the dimmable LED lighting system and method in greater detail with reference to the figures, various terms as used herein are explained below.
Spectral Power Distribution (SPD) describes the spectral power per unit area per unit wavelength of an illumination (radiant existence) or more generally, the per-wavelength contribution to any radiometric quantity.
Correlated Color Temperature (CCT) is a specification of the color appearance of the light emitted by a light source (e.g., a lamp), relating to its color to the color of light from a reference source when heated to a particular temperature. The CCT may be measured in degrees Kelvin (K). The CCT rating for a light source is a general “warmth” or “coolness” measure of its appearance. However, opposite to the temperature scale, light sources with a CCT rating below 3200 K are usually considered “warm” sources, while those with a CCT above 4000 K are usually considered “cool” in appearance.
Duv or Delta uv is the shortest distance between the chromaticity point in 1960 uv space to the Planckian locus. It is described by a positive number if the chromaticity point is above the Planckian locus and by a negative number if it is below the Planckian locus.
Planckian Locus (also referred to as “Black Body Locus”) is the path or locus that the color of an incandescent black body would take in a particular chromaticity space as the black body temperature changes.
Color Rendering Index (CRI) is a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with ideal or natural light sources. The CRI system is administered by the International Commission of Illumination (CIE). The CIE selected fifteen test color samples to grade the color properties of a white light source. The first eight samples R1-R8 are relatively low saturated colors and are evenly distributed over the complete range of hues. The first eight samples are employed to calculate the general color rendering index Ra. The general color rendering index Ra is simply calculated as the average of the first eight color rendering index values R1 through R8. The sample R9 is a value for a saturated or deep Red, which is important for interior lighting applications.
Turning to the figures,
CCT=a*dim(b+c/dim)+d,
The dimming color curve of the LED lighting system 100 may instead be configured to fit the dimming color curve of an incandescent light source such as defined by the following equation:
CCT=2920+396ln(x)+88.7ln(x)2+11.6ln(x)3
The LED driver 110 receives power from a power source 20, and may receive light settings such as a dimming level from a dimmer controller 10 or a remote device via the communication device 160. The dimming level may correspond to a dim percentage or dimming step over a dimming region. In operation, the LED driver 110 selectively drives current to each of the first, second and third types of LED light sources 150 via respective first, second and third channels. The current is selectively driven according to predefined power ratios according to the dimming level. The predefined power ratios may be stored locally in a memory 120 of the LED driver 110 or in an external memory accessible by the LED driver 110.
The communication device 160 provides for wireless or wireline communication with a remote device(s) (e.g., a tablet, smartphone, wireless remote controller, computer, server, etc.). The LED lighting system 100 may receive commands from the remote device. For example, as previously noted, the LED lighting system 100 may receive light settings, such as a dimming level, from the remote device via the communication device 160. The LED lighting system 100 may also download or receive data, such as the new or updated predefined power ratios from a remote device or system, via the communication device 160, for storage in an accessible memory (e.g., the memory 120).
Although the exemplary LED lighting system 100 is described with three different types of LED light sources having different SPD curves (characteristics), the system may include three or more different types of LED light sources. The LED driver 110 can be a programmable multi-channel LED driver, which drives each channel using constant current reduction (CCR), pulse width modulation (PWM), hybrid of CCR and PWM, or any combination thereof. The LED driver 110 may be operated as a standalone or under control of a controller (e.g., a processor) of the LED lighting system.
Various exemplary embodiments of an LED lighting system with incandescent style dimming are described below along with their spectral properties. In the first embodiment, the LED lighting system is configured with a general CRI of Ra that is greater than 80. In the second embodiment, the LED lighting system has a general CRI of Ra that is greater than 90, where one of the types of LED light sources on one channel has an Ra greater than or equal to 90 and the other types of LED light sources on the other channels have an Ra less than 90 (e.g., 80<Ra<90).
In the first embodiment, the dimmable LED lighting system includes first, second and third types of LED light sources with selected SPD curves on first, second and third channels, respectively, to provide for incandescent style dimming. The LED lighting system has the following spectral properties on the first, second and third channels:
20≦α1≦35, 35≦β1≦58, and 1.63≦γ1≦1.79 on the first channel,
12.8≦α2≦17.85, 46≦β2≦66, and 3.6≦γ2≦3.8 on the second channel, and
7.7≦α3≦13.7, 80≦β3≦155, and 10.2≦γ3≦11.6 on the third channel, where
S(λ) is a function of the SPD curve which reflects spectral power versus a wavelength of an LED light source,
I1 is {Max[S(λ)]} in a wavelength range of 400 to 500 nm,
I2 is {Min[S(λ)]} in a wavelength range of 420 to 550 nm,
I3 is {Max[S(λ)]} in a wavelength range of 500 to 700 nm,
α1=I1/I2, β1=I3/I2 and γ1=I3/I1 on the first channel,
α2=I1/I2, β2=I3/I2 and γ2=I3/I1 on the second channel, and
α3=I1/I2, β3=I3/I2 and γ3=I3/I1 on the third channel.
In this embodiment, the LED lighting system may have the following relationship between the channels.
α1:α2:α3=(from 2.3 to 3.8):(from 1.2 to 2.1):1,
β1:β2:β3=(from 0.35 to 0.52):(from 0.41 to 0.72): 1, and
γ1:γ2:γ3=(from 0.13 to 0.17):(from 0.31 to 0.36):1.
Examples of three SPD curves S1(λ), S2(λ) and S3(λ) of the first, second and third types of LED light sources on respective first, second and third channels are shown in
α1=25, β1=42, or γ1=1.73 on the first channel,
α2=15, β2=55, or γ2=3.65 on the second channel, or
α3=9.5, β3=103, or γ3=10.8 on the third channel.
For the SPD curves shown in
Table A of
In the second embodiment, the dimmable LED lighting system also includes three different types of LED light sources with selected SPD curves to provide for incandescent style dimming. The LED lighting system includes first, second and third types of LED light sources on first, second and third channels, respectively. In this example, the LED lighting system has the following spectral properties on the first, second and third channels:
20≦α1≦35, 35≦β1≦58, and 1.63≦γ1≦1.79 on the first channel,
7.7≦α2≦13.7, 80≦β2≦155, and 10.2≦γ2≦11.6 on the second channel, and
the third type of LED light source is one of an amber (e.g., a phosphor converted (PC)-amber), red-orange or red LED light source on the third channel,
where
I1 is {Max[S(λ)]} in a wavelength range of 400 to 500 nm,
I2 is {Min[S(λ)]} in a wavelength range of 420 to 550 nm,
I3 is {Max[S(λ)]} in a wavelength range of 500 to 700 nm,
α1=I1/I2, β1=I3/I2 and γ1=I3/I1 on the first channel,
α2=I1/I2, β2=I3/I2 and γ2=I3/I1 on the second channel, and
α3=I1/I2, β3=I3/I2 and γ3=I3/I1 on the third channel.
In this example, the first type of LED light source on the first channel may have an Ra greater than 80, and the second type of LED light source on the second channel may have an Ra greater than 90. The LED lighting system may have the following specific values for α, β, and γ on the first and second channels:
α1=25, β1=42, or γ1=1.73 on the first channel, or
α2=9.5, β2=103, or γ2=10.8 on the second channel.
The LED lighting system is configured to drive current on each channel according to the predefined power ratios (e.g., ratios of signal strength) therebetween such as shown on the left side in Table B of
Table B of
In the second embodiment, the LED lighting system has a general CRI of Ra greater than 90 throughout the dimming region, where one of the three types of LED light sources has an Ra greater than 90 and the other two of the three types of LED light sources have an Ra less than 90 (e.g., 80<Ra<90). Furthermore, the LED lighting system has a value of R9 greater than 50 throughout the dimming region, where none of the three different types of LED light sources have a R9 greater than 50.
At reference 1204, a LED driver is configured to control the supply of current to the first, second and third types of LED light sources on first, second and third channels respectively at predefined power ratios that correspond to dimming levels over a dimming region of the dimming color curve.
At reference 1206, the LED lighting system is provided with the different types of LED light sources and the LED driver.
At reference 1208, the LED driver may be updated to operate according to new predefined power ratios associated with an updated dimming color curve.
The LED driver and LED lights sources may be assembled before or after configuring the LED driver to operate according to a set of predefined power ratios.
At reference 1304, a LED driver is provided which selectively controls current to the first, second and third types of LED light sources on first, second and third channels respectively at predefined power ratios. The predefined power ratios correspond to dimming levels over a dimming region of the dimming color curve, and may be stored in memory.
At reference 1306, a determination is made whether to update the dimming color curve of the LED lighting system. If not, the LED lighting system operates according to the predefined power ratios stored in memory. Otherwise, at reference 1308, the LED driver is updated to operate according to new or updated predefined power ratios associated with an updated dimming color curve. The LED lighting system can receive data for the new or updated predefined power ratios from a remote device via a communication device, and store the data in the memory.
The LED lighting systems described above in the present disclosure are provided as examples. The dimmable LED lighting system have been described as being modeled to provide for incandescent style dimming; however, the LED lighting system and method may provide for any style of dimming with adjustable color temperature by utilizing predetermined ratios of peaks and valleys (e.g., I1, I2 and I3) in the selected SPDs of the different types of LED light sources on each channel. The LED lighting system may include any number of different types of LED light sources and channels. For example, for a n-channel LED lighting system, αn=I1/I2, βn=I3/I2 and γn=I3/I1 on the n-th channel.
Furthermore, the LED lighting system may include light sources in which the LEDs may or may not be coated with phosphor material(s) depending on the desired spectral properties. For example, the LED can have an emitting peak wavelength in the region between 380 and 500 nm, such as a typical blue, ultra-violet (UV) or near UV LED. The substrate material for the LED can be GaN, Sapphire, Silica or other suitable material.
If phosphor is not deposited on the LED, it can have any peak or dominant wavelength in the region of 380-500 nm. If any phosphor material has already been deposited on the LED as in cool white LEDs, the CCT may be changed by placing another phosphor layer over the LED. This other phosphor layer can be considered a remote phosphor layer on top of the cool white LED. The phosphor layer can be located directly over the cool white (or blue LED) or can be remotely positioned anywhere in the mixing chamber in proximity to the LED.
A phosphor layer can be formed from phosphors, such as selected from YAG, LuAG, Nitride, Oxy-Nitrides, Oxides, Sulphides, Silicates or other suitable phosphors for LED lighting applications. The phosphor layer can be coated with either one or more of the listed phosphors, or a combination thereof. The phosphors can be either directly deposited on the LED substrate, deposited on a lens or translucent rubber sheet, or screen printed on a silicone layer with a combination of phosphors. The matrix is defined as the medium in which the phosphor(s) are placed, and can be either one or a combination of those described above. Phosphors can be positioned either on the chip or anywhere in the light mixing chamber. If phosphor is positioned such as a remote phosphor, the predefined mixture for the specific channel of the LED lighting system is not necessarily limited to only one combination.
In addition, words of degree, such as “about”, “substantially”, and the like are used herein in the sense of “at, or nearly at, when given the manufacturing, design, and material tolerances inherent in the stated circumstances” and are used to prevent the unscrupulous infringer from unfairly taking advantage of the invention disclosure where exact or absolute figures and operational or structural relationships are stated as an aid to understanding the invention.
Although specific example embodiments of the invention have been disclosed, persons of skill in the art will appreciate that changes may be made to the details described for the specific example embodiments.
