Many ENERGY STAR certified bulbs come in warm colors to match the yellowish light of incandescent bulbs, but you can also choose cooler colors with whiter or bluer light. Choosing the Right Color: Light color is measured on a temperature scale referred to as Kelvin (K). Lower Kelvin numbers mean the light appears more yellow; higher Kelvin numbers mean the light is whiter or bluer. Most ENERGY STAR certified bulbs are made to match the color of incandescent bulbs at 2200-3000K. For a whiter light, look for bulbs marked 3500-4100K. For bluer white light, look for bulbs marked 5000-6500K.