The 20000K metal halide bulb offers excellent coloration and good intensity. It is crisp-white with a strong blue tint. It brings out the fluorescent pigments in corals nicely. Fluorescent supplementation is usually not necessary, but can be used for added intensity and to simulate dawn and dusk. An excellent choice for reef tanks 18" or deeper. on how the different Kelvin ratings appear and more information on metal halide bulbs.