IES Definition: Colour Temperature is the absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source.
The Correlated Colour Temperature (CCT) is a specification of the colour appearance of the light emitted by a lamp, relating its colour to the colour of light from a reference source when heated to a particular temperature, measured in degrees Kelvin (K).
The colour temperature of white light generally speaking is from 2000K (red or warmer hue) up to 8000K (blue or cooler hue).
The CCT rating for a lamp is a general "warmth" or "coolness" measure of its appearance. However, opposite to the temperature scale, lamps with a CCT rating below 3200 K are usually considered ìwarmî sources, while those with a CCT above 4000 K are usually considered "cool" in appearance.
Common colour temperatures are 2700K (incandescent colour), 3000K (typical halogen), 4000K (commercial neutral/warm white), 5000K (cool white) and 6000K (day/sky white).
The following graphic shows three colours, 2700K, 4000K and 6000K from left to right.
The lights shown are CREE MC-E LED downlights:
The CCT specification for a light source gives a good indication of the lamp's general appearance, but does not give information on its specific spectral power distribution which can change the reflected colours of objects, skin tones, paint etc.
Therefore, two lamps may appear to be the same colour, but their effects on object colours can be quite different.
Below is a comparison chart of three different CCTs with their relative spectral power distribution:
What colour LED lights are available?
LED technology covers a wide range of colour temperatures, and it is possible to create virtually all colours during the manufacturing process.
Other than the normal white colour temperatures, colours such as red, blue, green, yellow are often expressed by their wavelength measured in nanometers (nm), and once again LED technology covers all these wavelengths.
The visible colour spectrum and its wavelengths are shown in this image:
Which colour LED light suits my application?
Most people have grown up with incandescent globes in their home which emit a warm white colour (2700K), and it would seem that many people prefer the intimacy of this colour. However, the colour temperature you choose for your home is entirely up to you.
With this in mind, it is important to note how colour temperatures affect you and your surroundings. For example, warmer colours often set a relaxed mood, while cool white light creates a more focused, mentally-alert environment.
Typically, designers use cooler colours in office and shop environments as it helps staff and customers to focus or concentrate on the work at hand, and products are displayed more favourably. In industrial applications cooler light helps visibility and improves safety.
We recommend our customers use a cooler or neutral colour light in the office, bathroom, laundry, kitchen and garage, and places where increased concentration and attention to detail are required.
How does LED light colour affect light output?
Even though LED lights come in a wide range of colour temperatures, the majority of white LEDs currently available are in fact made using royal blue LED chips with a phosphor coating applied to the surface. The phosphor plate or coating determines the colour temperature, colour rendering index(CRI) and efficacy.
The following video explains this process:
With LED technology, there is a consistency in that the higher colour temperature LED (ie. more blue) will produce more lumens per watt than a warmer coloured LED consuming the equivalent power. This slight inrease in power requirment occurs because more filtering is applied via the phosphor plate to achieve the warmer colour, and efficacy is therefore slightly reduced.
Generally, given the same light power output, warmer-coloured LED lighting systems will use slightly more power overall, than cooler-coloured systems.