The glass will filter/block some light and, well, if you need it to be waterproof in your grow set up then there's something wrong. Having worked with a company that made all sorts of lights, I've seen what a single 3mm thick piece of glass can do regarding attenuating light output as well as filtering out certain colours (blues tended to be lower in intensity with a piece of plain glass in the way, guess it depends on the actual make up of the glass).
Best to remove anything that could interfere with the light output, and it *should* also help with dissipating any heat from the COB in the floodlight as everything isn't so enclosed.
