How light affects color

Many of us have encountered a certain problem when choosing a paint for an interior. After being applyed on the walls, the paint color can look completely different from what was on the sample. There are several reasons why this can happen.

Daylight is the purest light which reveals the depth of colours to maximum. Artificial light shows much poorer colour, so when choosing colour for an interior you must be ready that the colour will be different in daylight and artificial light.
 It all depends on two factors: light temperature and color rendering index. Light temperature is measured in Kelvins. When light has a high temperature its color is cool and vice versa. So incandescent light, which is relatively cool (about 2500 K) has a warm yellow colour, and fluorescent light that reaches to about 8000K has a cold bluish colour.
The color rendering index (CRI) shows how precisely the light shows a colour. It is measured in points from 0 to 100. The CRI of natural daylight is 100. The CRI of incandescent light is the same, but still it doesn’t provide as pure colors as daylight does. The reason is the light temperature. Daylight is in the centre of the light spectrum with temperature about 5000-6000K. Thanks to this it renders all the colours of the spectrum.
Incandescent light is in the cold part of the light spectrum, which means it is stronger at the red-yellow part and weak at the blue part. So it doesn’t render different tones of blue and green gets a yellowish tint under it. In general, incandescent light is weak at rendering cold colours so a cold colour will seem warmer under it.
Another important aspect to take into account is what direction a particular room faces, as the daylight differs depending on it. Northern and Eastern lights add blue to the colors, while Southern and Western lights add red. So in a South-facing room the color won’t differ much under daylight and incandescent light, while in a North-facing room the difference will be dramatic. Also the daylight differs during the day. At the sunrise and sunset its temperature is lower, so it has a reddish colour, while during the day it gets hotter and its colour gets colder and gains more blue.
Taking all this into account, some preparatory work has to be done before choosing a color for a particular room.
What you can do, is to prepare color samples and examine them in that room under daylight during different times of the day and under incandescent light. Also if different rooms are to be painted in the same colour, you should check how the colour changes in them.
If you want the color to look good throughout the day, you can try to choose cooler colors for north-facing rooms, or rooms illuminated with fluorescent lamps, and warmer colours for south-facing rooms and if you are planning to use incandescent lamps.