While D40XTI fixtures have a sealed glass lens for outdoor or IP65 environments, diffusion lenses are stacked on top of this glass, and vulnerable to the elements. This clear glass lens is designed to be installed after the diffusion lenses and acts as a barrier to protect them from the elements.
Clear glass lens to protect D40XTI diffusion lenses
Not required, but recommended when using fixtures in IP65 environments for extended periods of time
Not included with base D40XTI fixture (which has clear glass lens for LEDs, but not diffusion lenses)