Heres what we recommend for most plants.
Germination, propagation and the early stages of vegetative growth, use a Blue spectrum T5 type light or a blue spectrum CFL Lamp
During the Vegetative stage use a Metal Halide Lamp. plants under Metal halide Lamps grow with closer branch internodes than those grown under Dual Spectrum or Standard HPS Lamps. This will result in plants being more bushy rather than shooting up to the light and will also have more flowering sites due to the extra branching.
In the Flowering stage we recommend a Dual Spectrum Lamp is used. This will provide the red spectrum of light that the plant requires, but also has a small amount of blue spectrum that will help reduce "stretch" that you would get with a traditional HPS Lamp. For Pepper plants use Metal Halide rather than change to a Dual Spectrum Lamp.