The OttLite 508 Illumination 13W T-4 replacement tube bulb is specially formulated to make reading and seeing everything easier. Delivering the right mix of brightness and contrast, we bring true colors and comfortable clarity to your world so you can enjoy your time even more. 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 13W OttLite tube is roughly equivalent to that of a 60W 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.Details:Replacement bulb type HFor use only as a replacement bulb with specific OttLite lampsTrue colors, clear details and reduced eyestrainLow-heat, low-glare illuminationEnergy efficientRated to last up to 10,000 hours