To indicate the hue of a specific type of light source, the standard procedure is to measure its color temperature in degrees Kelvin. For example, for suggesting realistic colors of lights in a 3D scene, you can use a Color Temperature chart. Typically, the white balance of a video camera or a film stock is used as the base for relating visible colors. For this, two settings are used most commonly. The first is the indoor color balance, set at 3200K and the other is the daylight color balance, set at 5500K.
Measuring the hue of light as a ‘temperature’ was started by the British Physicist William Kelvin in the late 1800s. When heating a block of carbon, he noticed that it glowed and produced a range of different colors at different temperatures. Beginning from a black cube, it first produced a dim red light, moving to a bright yellow as the temperature increased. Eventually, it glowed with a bright blue-white at the highest temperature.
To honor William Kelvin, the unit of measurements of color temperature is degrees Kelvin, a variation on degrees Centigrade. Unlike the Centigrade scale, which starts at the temperature of freezing water, the Kelvin scale starts at -273 degree Centigrade, also known as ‘absolute zero’. However, when attributing color temperatures to different types of lights, it is usual to correlate them based on visible colors matching a standard black body. Therefore, the stated color temperature is not the actual temperature at which a filament is burning.
Now, an LED, available as a simple chip on board or COB package, can be tuned for its color temperature. The LED manufacturer Everlight has introduced this as the world’s first color-temperature tunable LED.
Immediately following brightness dimming, the next most desirable feature for users of LEDs is to be able to tune the warmth of the light output. For example, some people prefer a ‘warm’ colored light to a ‘cool’ type of illumination. Accordingly, manufacturers generally implement this feature by using multiple LEDs ranging from cool white to warm white, placing them behind a diffuser.
Everlight provides a very compact solution with its CHI3030 27V/29W series. They have packaged the LEDs behind concentric layers of phosphors. This offers different color temperatures of white as setting a precise color-temperature mix is simple now – just light up the required numbers of warn white or cool white LEDs.
Consuming 29W at 27V, the 30x30mm COB CHI3030 from Everlight is the largest such multi-chip solution for a tunable temperature LED. You can select from among different tunable ranges such as 4745-7050K for the KY Cool-White series to the 2500-5700K for the KH Warm-White series. The typical luminous flux output from the LEDs is 2990 lumens for the 5700K cool white and 2760 lumens for the 2700 warm white. Everlight makes similar other series of LEDs with fewer concentric phosphor rings that operate down to 9W.
Everlight expects such color-temperature tunable LEDs to see mainstream use within the next few years. Adding such extra color tuning flexibility allows manufacturers to calibrate their products easily and precisely at low costs.
