4. Lens for led high bay The lens is sometimes neglected by designers. Actually the refraction of light will result in light decay, and the lens speed finally dramatically affect luminous flux. Lens with fairly good lens speed can reach 93. Lens itself is an important part of cost, so some manufacturers use cheap lens to save cost of LED Lights. Those cheap lenses have the lens speed of around 70, but customers can hardly tell the difference through the eyes. The lens speed can actually be tested using instruments, and lens made by worse material will turn yellow after short period of usage.