News Column

Researchers Submit Patent Application, "Dimmable Led Light Fixture Having Adjustable Color Temperature", for Approval

July 30, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors BADDELA, Srinivasa (Streamwood, IL); SERRA, John (Pingree Grove, IL); GIELNIEWSKI, Michael (Bartlett, IL), filed on March 11, 2014, was made available online on July 17, 2014.

The patent's assignee is Juno Manufacturing, LLC.

News editors obtained the following quote from the background information supplied by the inventors: "The concept of color temperature is based on the comparison of a visible light source to that of an ideal black-body radiator. The color temperature (CT) scale assigns numerical values to the color emitted by the black-body source being heated, measured in degrees Kelvin (K). A black-body radiator is a theoretical material having perfect absorptivity at all wavelengths, making it the best possible emitter of thermal radiation.

"One typically thinks of color temperature in terms of the 'whiteness' versus 'warmness' of the light source, i.e., 'Daylight White' is 5000-6500 K, 'Cool White' is 3500-5000 K, 'Warm White' is 3500 K and below. Thermal light sources, such as incandescent lamp filaments, are called 'incandescent radiators', and have a spectral power distribution (SPD) more uniformly spread throughout the visible spectrum. Light sources that are not incandescent radiators, which do not exhibit visible spectrum radiation at all wavelengths of the spectrum, are measured according to a 'correlated color temperature' (CCT) scale. The CCT scale is adjusted according to human perception. White LEDs are measured using the CCT scale.

"It is well-known that the color of the light produced by incandescent lamps changes when the lamp is dimmed. When the incandescent lamp is at full rated power, its correlated color temperature (CCT) is usually within the range of 2700 K-3300 K. However, when the incandescent lamp is dimmed, the CCT changes to as low as 1700 K, approximately the color of a match flame. To the human eye, the incandescent bulb appears to go from white to yellow, or to give a 'warm glow' when dim. For many years, this inherent characteristic of incandescent bulbs has been seen as a feature used with AC dimmer modules to create a warm and cozy environment in restaurants, hotels, theaters, homes, etc.

"LED light fixtures, which became popular in recent years because of their energy efficiency, give off light that does not normally change color when the fixture is dimmed. The white light from an LED light source has a constant CCT across the entire range of the AC dimmer module. Hence, even at lower light levels when dimmed, the white light given off by LED light fixtures has been perceived as unusual or unnatural, particularly when used in the aforementioned environments when trying to create a warming lighting effect. LED lighting manufacturers have been aware of this problem, but have yet to find a way to accurately duplicate the 'warm glow' dimming characteristics of incandescent bulbs in a cost-effective manner.

"One way to simulate the 'warming with dimming' characteristic of an incandescent lamp with an LED light source is to optically mix white LEDs with amber (yellow/orange) LEDs, and control their currents in such a manner that the mixed color light from the LED combination changes from the 3000 K white light to a more amber-yellowwhite color with dimming. Traditionally, LED systems performing mixing of two or more colored LEDs use individual drivers controlling 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. U.S. Pat. No. 7,288,902 to Melanson, incorporated by reference herein, describes such a circuit having multiple light sources to vary the color temperatures in response to changing dimming levels. The light source driver provides individual drive currents to each light source in response to the selected dimming level in order to achieve the desired color temperature. At least a two-channel LED driver must be used to power an amber LED in addition to a white LED array in this circuit.

"The use of individual LED drivers, or a multi-channel output LED driver, to control each LED colored array, has several disadvantages. First, and most importantly, is the additional cost. As LED lighting becomes more prevalent, designers seek the most cost-effective alternatives. Second, complexity and reliability issues demand the simplest solutions. Custom multiple-channel LED drivers designed for specific types of dimmers are not a preferred lighting solution. Third, if the warming-while-dimming function could be accomplished inside the LED light engine using only the two inputs provided by a single-channel LED driver, the LED light engine could be used with most any LED driver, and dimmable with most any AC dimmer module.

"A need, therefore, exists for an LED circuit arrangement and LED light fixture that can be used with a single-channel variable-DC LED driver to simulate the color temperature changes of incandescent lamps as dimming levels change."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Aspects of the present disclosure are directed to electronic circuitry and devices for color-mixing LEDs during dimming to achieve adjustable color temperature. According to one embodiment, a dimmable LED light fixture is disclosed, which comprises first and second LED light sources, the first LED light source producing light visibly different in color from that of light produced by the second LED light source; an LED driver having two input terminals configured to be connected to a dimmable AC power source having a dimmer module, the LED driver configured to power the LED light sources by providing a single-channel variable-DC power output requiring no more than two electrical connections to the LED light sources, the first and second LED light sources coupled in parallel across the LED driver output; and a current regulator coupled in series with only the second LED light source, whereby the current in the second LED light source remains substantially constant as the LED driver DC output power is decreased when the AC power is reduced by the dimmer module, thereby altering the color of the light produced by the combination of the first and second LED light sources.

"According to another embodiment, a dimmable LED light engine circuit is disclosed, having first and second LED light sources, the first LED light source producing light visibly different in color from that of light produced by the second LED light source; and further having a third LED light source producing light substantially the same color as that produced by the first LED light source, the third LED light source connected in series with the parallel combination of both the first and second LED light sources.

"According to another embodiment, a dimmable LED light fixture is disclosed having first, second, and third LED light sources, the first and second LED light sources producing white light, the third LED light source producing colored light, each LED light source having first and second terminals; an LED driver having two input terminals configured to be connected to a dimmable AC voltage produced by a dimmer module, the LED driver configured to power the LED light sources by providing a single-channel variable-DC current source having two output terminals, the first output terminal connected to the first LED light source first terminal, the second and third LED light source first terminals connected to the first LED light source second terminal, and a current regulator having first and second terminals, its first terminal connected to the third LED light source second terminal, the current regulator second terminal and the second LED light source second terminal connected to the LED driver second output terminal, whereby the single-channel variable-DC-current provided by the LED driver passes through the first LED light source series current path and is split between the second and third LED light source parallel current paths, and whereby the current in the third LED light source path remains substantially constant as the LED driver output current is decreased when the AC voltage is reduced by the dimmer module, thereby altering the color of the light produced by the combination of the LED light sources.

"A dimmable LED light engine is also disclosed, having first and second input terminals adapted for connection to an LED driver, the LED driver configured to be connected to an AC power dimmer module, the LED driver configured to power the LED light sources by providing a single-channel variable-DC power output requiring no more than two electrical connections to the LED light sources, the dimmable LED light engine comprising: first and second LED light sources coupled in parallel across the first and second input terminals, the first LED light source producing light visibly different in color from that of light produced by the second LED light source; a current regulator coupled in series with only the second LED light source, whereby the current in the second LED light source remains substantially constant as the LED driver DC output power is decreased when the AC power is reduced by the dimmer module, thereby altering the color of the light produced by the combination of the first and second LED light sources. The dimmable LED light engine may further comprise a third LED light source producing light substantially the same color as that produced by the first LED light source, the third LED light source connected in series with the parallel combination of both the first and second LED light sources.

"According to one aspect of the disclosure, the dimmable LED light fixture does not need to have an individual LED driver for each LED light source, or have a multi-channel output LED driver, to control the white and amber LED arrays separately. The present design can be implemented with any type of off-the-shelf dimmable LED driver that performs amplitude dimming. In this way, an existing LED light fixture can be retrofit with the LED light engine according to the present disclosure, depending upon the LED voltages involved, without having the LED light fixture replaced. This allows the customer to retrofit an existing LED light fixture with an LED light engine that accomplishes the warming-while-dimming feature.

"Aspects of the present disclosure further provide for the use of a microcontroller to provide more precise control of the current regulator, which, in turn, provides more accurate simulation of the characteristic black-body curve of an incandescent lamp during dimming.

"Another aspect of the disclosure provides for accurate color temperature correction at very low dim levels to closely simulate the incandescent lamp dimming curve, and to avoid color shifts during the lower dimming range upon an increase in AC power.

"The foregoing and additional aspects and embodiments of the present invention will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments and/or aspects, which is made with reference to the drawings, a brief description of which is provided next.

BRIEF DESCRIPTION OF THE DRAWINGS

"The following Figures depict certain illustrative embodiments of the invention in which like-reference numerals refer to like elements. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way.

"FIG. 1 is an electrical block diagram of a dimmable LED light fixture in accordance with an embodiment of the present disclosure;

"FIG. 2 is a graphical representation of the relative LED currents in the circuit of FIG. 1 versus the percentage of dimming provided by the dimmer module;

"FIG. 3 is an electrical block diagram of another embodiment of a dimmable LED light fixture in accordance with the present disclosure;

"FIG. 4 is a graphical representation of the relative LED currents in the circuit of FIG. 3 versus the percentage of dimming provided by the dimmer module;

"FIG. 5 is an electrical block diagram of an alternative embodiment of a dimmable LED light fixture utilizing a microcontroller for controlling the current regulator;

"FIG. 6 is a graphical representation of the relative LED currents in the circuit of FIG. 5 versus the percentage of dimming provided by the dimmer module;

"FIG. 7 is an electrical block diagram of a dimmable LED light fixture in accordance with another embodiment of the present disclosure; and

"FIG. 8 is a flowchart showing the operational steps performed by the microcontroller of FIGS. 5 and 7 in generating the dim control signal for the current regulator."

For additional information on this patent application, see: BADDELA, Srinivasa; SERRA, John; GIELNIEWSKI, Michael. Dimmable Led Light Fixture Having Adjustable Color Temperature. Filed March 11, 2014 and posted July 17, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4509&p=91&f=G&l=50&d=PG01&S1=20140710.PD.&OS=PD/20140710&RS=PD/20140710

Keywords for this news article include: Electronics, Juno Manufacturing, Juno Manufacturing LLC, Microcontroller.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Electronics Newsweekly


Story Tools






HispanicBusiness.com Facebook Linkedin Twitter RSS Feed Email Alerts & Newsletters