Phosphorous coated to promote blue and red spectrum so you can veg and bloom, more blue light than red, a cheap way to get started. However bulb requires replacing every nine months because lamp can become volatile. Costs more to run and maintain compared to with High Pressure Sodium [HPS], Metal Halide [MH] or fluorescents. We recommend 1000 Watt, High Pressure Sodium [HPS], air cooled lighting for general purpose lighting.