Optics are the lenses, reflectors, light guides, diffusers, and related surfaces that control how light leaves a lamp. They form the light pattern, direct useful light to the work area, and help manage cut-off, uniformity, stray light, and glare. Well-designed optics balance width, reach, uniformity, efficiency, and glare control for a particular task. Small changes in optical geometry or surface finish can significantly change the distribution even when the same LEDs are used. The optical system should therefore be evaluated through the named light pattern and photometric performance of the complete product.