Color temperature:

3500 K or less = Warm
3500 K to 4000 K = Neutral
4000 K to 6000 K = Cool

Reference color temperatures:

2500 K = 40W incandescent bulb
6500 K = Daylight

Color rendering index range:

60 - 65 CRI = Low
70 - 85 CRI = Moderate to High
90 and higher = Very High

Reference CRI:

100 = standard incandescent source

Color Temperature is the color appearance of the light produced by a lamp (bulb). It is also the color appearance of the lamp (bulb) itself.

Color Temperature is expressed on the Kelvin scale: example, 3500 K or 4100 K

The lower the Kelvin number the "warmer" the appearance. The higher the Kelvin number the "cooler" the appearance. Warm light has more red and orange wavelengths. Cool light has more blue and green wavelengths.

Choice of color temperature is based on psychological factors. Warm light sources bring out some flesh tones and make environments feel "cozy". Warm color temperature is generally preferred in residential and some retail or hospitality applications. Cool light sources make environments feel "efficient" or "utilitarian" and are used more often in office applications.

Color Temperature should not be confused with Color Rendering, which describes how a light source makes the color of objects appear. Light sources are rated according to a Color Rendering Index (CRI) on a scale of 0 to 100. The higher the number the better the light source's ability to accurately render the color of an object.

It is possible to choose a "warm" or "cool" color temperature light source with either a low CRI or a high CRI. When comparing the CRI of different light sources make sure each light source has the same color temperature.