Plastic? Sorry, just couldn't resist. :icon_bigg
There is a thread - for which I am remiss in not referencing - that Hoppy did that shows a bunch of PAR values for the various LED fixtures (as well as other lighting etc - it's an amazing read) where the bottom of the barrel LED was the Marineland Double-Bright. Some folks consider the Double-Bright a "fish only" light, and figure the Single Bright is even lower than that. Also, given the cost of the fixture, I wouldn't go out and actively purchase one. I've had a Double Bright myself, and it wasn't anything stellar. It's also quite outdated with the current technology out there now. If you just wanted the shimmer affect, and were coupling it with a 2nd plant growth light, that might be a good use.
Oh, to the OP - my understanding on your title is that you are referring to the "Marineland Single Bright" unit, and not a generic, bright, single LED. If it is the latter, my apologies, my response was clearly going on the Marineland unit.