A method used to characterize the spectral properties of a light source and specify the appropriate light source type in architectural design; light sources of the same color can vary in quality (CRI is used to describe light source quality); lower color temperatures are warmer (yellow/red) while high color temperatures are cooler (blue); the standard unit for color temperature is Kelvin, K (e.g. candlelight is 1500k, daylight at noon is 5500k).