The large, thin plastic tubs that they sell cheese puffs and/or packets of pretzels in are perfect for a floodlight housing.
(the one's I'm using are what Costco sells their Halloween Pretzel packs in - they're about a foot around, just over a foot tall, and thin plastic)
Take the tub, cut the open end off (or not - however, it blocks a lot of light if you don't), spray paint the INSIDE of the tub (I've used brown and black, but I suppose green would work or whatever color - just keep in mind that is the color people will see during the daytime).
Once the paint's dried (I recommend a couple of coats to keep it opaque), cut a slice half way down one side - this is what you're going to slip around the base of the floodlight holder.
So, place the cut at the base of the holder, and slide the tub up until the light is surrounded as needed - the one's I've done keep out the elements fairly well, and keep the light from being broadcast except for where I really want it. Additonally, they do not get hot, as the open end allows enough air in to channel the heat away.
(sorry - don't have pic's of the holders to show, but it's a pretty simple design)