The color of light, expressed in Kelvins (K). The sun is about 5800 Kelvins. This is called a "temperature," because the hotter fire gets, the more it changes from a warm yellow glow to white.
The lower the Kelvin rating, such as the common incandescent/tungsten bulb, the warmer, softer and more yellow the light. The higher the K number, the cooler, whiter and bluer the light.
This rapid-start linear fluorescent lamp is a special
application bulb manufactured to the highest standards. Utilizes blacklight phosphor (356㎚) with a blue glass filter to eliminate visible light Fits 4-foot (nominal) linear fluorescent fixtures designed for 40-watt rapid-start (or pre-heat*) ...