There are a lot of posts about overvolted halogen MR16s for the front. I have two DIYs myself, and they are extremely bright. However, I've never seen or heard of anyone using a red MR16 20 watt as their tail light (w/o flash mode, most likely). I know that the red lens diminishes the overall lumens, but given how bright these things are to begin with (especially when overvolted) I can't see that being a problem. Seems like you'd end up with something on a par with a Dinotte 140L or brighter.
Has anyone tried this?