This is a popular question, because different shades on the color spectrum product different effects. The natural color spectrum starts with UV rays, then blends to cooler hues, meets in the middle for yellow and whites, then moves on to warmer hues such as red and orange, and ends with infrared. Generally, warmer shades such as reds, oranges, yellows and and IR rays are preferred for initial growth for seedlings and younger plants. Cooler hues such as blues, greens, and UV rays are ideal for leafy growth and stem health. Most products out there on the market have a blend of both shades so they will be ideal for everything. Some of the higher end models allow users to adjust the coolness or warmth of their bulbs to focus on one specific stage of their plants growth. If you are serious about your indoor garden and want to see quick results, you may want to spend the extra money and opt for a design that will allow you to adjust the tone of your bulbs.