I've read, from multiple sources, multiple times, that 50 lumens is considered to be the lowest level of usable light for stage lighting. I've never obtained a definition for "usable light". Is that quite dim light, but provides a clear view of the subject? Or does that mean something that might be useful for accent or something, but not enough illumination to provide a clear view of the subject? I'm not quite clear on that. And let's say I have 100 lumens of light, but I gel the light with a filter that has a 50% transmission. That means I have 50 lumens on stage, or the lowest amount of "usable" light? What is the lowest amount of IR light? Somewhere on here was a discussion of using WFL PAR64s, with deeply saturated blue color filter run at like 5-10% as a source for an IR camera. Is this truly enough light, or was this a hypothesis?