Metal Halide bulbs have a slight bluish light and are primarily used for The vegetative (first) phase of Plant growth.The type of light produced From MH is near the spectrum closest to sunlight (5500 Kelvin) which Encourages normal growth. This Optimized Spectrum MH Grow Lamp allows you to Stretch your growing season to 365 days a year.Fine-tune Your lighting system to provide optimum spectral energy Levels that promote vigorous plant growth. Optimized Spectrum MH Grow Lamps provide high initial and Maintained lumen output with optimum spectral energyrequired For vegetative growth. Optimized Spectrum Metal Halide Grow Lamps are designed to Grow high quality, natural looking plants during all phases of their Growth cycles.