Energy efficient instant-on bulb, rated to last up to 10,000 hoursThe OttLite 508 Illumination 20-Watt screw-in bulb delivers the right mix of brightness and contrast to bring true colors and comfortable clarity to your world so you can enjoy your time even more. You'll see colors accurately so you can make selections with total confidence. And, you'll see fine print and details with ease under this unique low heat, low glare illumination that helps reduce eyestrain.The output of a 20-Watt OttLite bulb is roughly equivalent to that of a 75-Watt incandescent bulb. So, they use about 1/4 the amount of energy for the same amount of light. However, it's not just about energy-savings, it's also about the quality of the light.