ViaVolt HPS (High Pressure Sodium) Grow lights have an effective spectral distribution for plant growth. Standard High Pressure Sodium Grow Lights emit light in the yellow and red wavelengths of the electromagnetic spectrum, but for increased effectiveness these bulbs have been enhanced with additional blue wavelengths to maximize their performance for plant growth. High Pressure Sodium light helps stimulate flower and fruit production in plants more efficiently than other light sources designed for growing plants. It is best to use HPS Grow Lights for the fruiting and flowering phase of plant growth or in a 4:1 ratio of HPS to MH for best results. 90,000 Lumens, 2,000K, ET25 Lamp.