This refers to the number of LEDs that the lens is designed for. They can be for single LEDs or arrays of LEDs. Multiple LED lenses are ideal for wide area lighting, for example street lighting.
This includes the basic factors to consider when choosing an LED lens or reflector for your application. There is also information behind these factors to help you to make your decision.
Lumens is a measurement of total light output or in other words the brightness of the bulb. More lumens means it's a brighter light; fewer lumens means it's a dimmer light.