The ATI 39W 36" True Actinic T5 HO Lamp produces a violet-blue light that is designed to maximize fluorescence in capable corals and make livestock colors pop. Color spectrum peaks at 421nm. Usually just one per fixture is used to add additional fluorescence to the system. Recommended as a supplement to LEDs and metal halides and commonly used for sunrise and sunset applications in T5 set ups. 34 inches from end of pin to end of pin. For 36" T5 high output lighting fixtures. Made in Germany.