It is measured on an index from 0-100, with natural daylight and incandescent lighting both equal to 100. Lamps with a high color rendering index make objects appear more true to life.
Plants can grow better with a higher color rendering index light source.
But generally the higher the CRI the lower the lamp efficiency. Color Temperature Color temperature is a measure of the color appearance of light not the actual temperature. Daylight is considered to be around 5500K and plants grown under this light do quite well. The cost of the lamp increases as the color temperature goes up because of the rare materials required to fill the arc tube. Lumen A lumen is the unit that expresses the total quantity of light given of by a source, regardless of direction.