[xoxoxoBruce]

I thought a dichroic mirror passed, and reflected, half the light... but not so.

A dichroic filter or thin-film filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, Dichroic mirrors and dichroic reflectors tend to be characterized by the color(s) of light that they reflect, rather than the color(s) they pass.

Thanks for the edumacation, Beau.