Correlated color temperature (CCT) will tell you what hue and tone of white to expect from a specific bulb or fixture. CCT is measured in Kelvin (K), which is similar to degrees in Celsius. Different temperatures on the Kelvin scale represent different colors. For example, light at 2000K-3500K looks more orange/yellow and is called ultra warm or warm white, and as temperature increases in Kelvins, color changes to more of a “paper white” known as natural or neutral white (between 3500K and 5100K) and finally into a bluish-white known as cool white (5100K-20000K).

The colour temperature is mainly used to describe the light colour of a light source. Generally speaking, light sources with higher colour temperatures tend to be bluish and greenish, such as a clear sky; light sources with lower colour temperatures tend to be orange and reddish, such as ordinary incandescent lamps and tungsten halogen lamps. The natural light environment we live in, its colour temperature will change with the passage of time in the day, the sunrise and sunset time colour temperature is lower, showing warm yellow, and the midday time colour temperature is higher, the light colour is bluish.

Studies have shown that the colour temperature of lighting can affect the human body's circadian rhythm, body temperature, sensitivity level, and indirectly affect work efficiency, physical health and psychological mood. People's preference for lighting colour is mainly related to activity status, age, illumination level and local climate conditions. By the lighting comfort colour temperature and illuminance level of the relationship can be seen, low illuminance, low colour temperature lighting and high illuminance, high colour temperature lighting will make people feel happy and comfortable, while high illuminance, low colour temperature lighting will make people feel hot and stuffy, low illuminance, high colour temperature lighting will make people have a gloomy, dim, cold negative feelings.

Impact on work

High colour temperature light source can increase the excitement level of people's brain, so that attention can be focused, thus speeding up the reaction speed to transient events, and can improve the ability of human brain activity. Therefore, the office or reading room will usually use high colour temperature light source, in order to improve people's office efficiency and reading attention.

Impact on sleep

Low colour temperature light sources promote the secretion of melatonin, which reduces the speed of response to transient events. Therefore, sleeping environments such as bedrooms, hotels and B&Bs usually use lighting sources with lower colour temperatures to avoid suppressing the secretion of sleep-related melatonin and to help the body relax, which in turn benefits sleep and promotes good health.

Impact on Emotion

Warm and cool light environments with different colour temperatures can trigger people to have different psychological feelings and emotional experiences, which to a certain extent can affect their social behaviour. It has been found that people in a warm white light environment with a low colour temperature are more positive and energetic than those in a cool white light environment with a high colour temperature, and show a higher degree of tolerance in the social process and complain less about negative life events. For example, some high-end restaurants usually use low-colour temperature lighting to create a hazy, quiet atmosphere, so that people are more pleasant and relaxed dining to improve appetite.