The colour temperature or called correlated colour temperature of a light source is the temperature of an ideal black-radiator that radiates light of comparable hue to that of the light source. It is specified in Kelvin (K).
The colour temperature Low colour temperature under 3000K implies warmer (more yellow / red) light adopt by low temperature area , while high colour temperature above 5000K implies a colder (more blue) light with cool feeling always adopt by high-temperature area. 4000K with a neutral light not very warm neither very cool therefore more frequently be use.
Sunlight and incandescent light both emits visible light wavelength (380nm-760nm) with continuous spectrum, including red, orange, blue, green blue, purple. Gas discharge lamp with continuous spectrum could reproduce colours of various objects faithfully, however, gas discharge lamp with uncontinous spectrum will case varying degrees of colour distortion. effect of an illuminant on the colour appearance of objects by conscious or subconscious comparison with their colour appearance under a reference illuminant called colour rendering
CRI was developed to gauge different colour rendering of different illuminant. The CRI reports a unit less value that can differ between 0 and 100. The value 100 means that there is no difference in colour rendition between the light of the observed light bulb and the light of the reference illuminant. As a general rule “The Higher The Better”, light source with high (80-100) CRI’s tend to make people and things look better than light sources with lower CRI’s.