A forum thread is not a LSO course but I have some
super basic questions before I consider getting into the hobby, and I am not sure how else to get answers. I'm not even clear on what kind of laser power makes viewing a projection on a screen or wall safe or unsafe... I have no frame of reference other than owning a 5mW green pointer... which already seems scary bright!
My goal is to do basic home entertaining/DJ displays, and it is my hope to do so via entry-level commercial gear, as opposed to a Lasercube (cool though it is). I have a vague understanding of laser safety rules like 1) No beams into the sky 2) No beams into the crowd 3) Beams must be totally out of reach (ie, 10 ft overhead).
I have no practical understanding of how to set up a display though, and would really appreciate info on any of these questions. If it helps, I am sort of considering a Mobile Beat Mirage RGB, which has a total output power of 400mW--but I don't know enough yet to be 100% confident in that.
Is front projection on a white movie screen/wall safe?
Perhaps a better question is, at what power is light reflected from a screen no longer safe?
We have a home theater projector room with a seating area that is about 13 ft x 20 ft. Even if it's safe to view the image, I don't see how you could observe projector placement safety in such a small space.
(I see a million people on YouTube and Twitch projecting onto walls right behind them, but just because it's online doesn't mean it's a good idea, right?)
Is rear projection on a white movie screen/wall safe?
Same question, but for rear projection. Some light does come through the screen, after all. We have an outdoor portable projector screen which can work in front or rear projection mode. I
really hate the idea of aiming the laser towards people even if there's a screen there, though.
https://i.imgur.com/mR6nwvq.png
Is there a safe way to project onto trees?
If I was entertaining outside, I have a line of tall trees that could act as a screen. Not great for precision graphics, but it would be fun anyway. Here's a shot of the yard... It is about 150 ft to the treeline, and the tallest tree is about 140 ft tall. There's about a 100ft wide x 70 ft tall patch of tree branches that is pretty dense.
https://i.imgur.com/M3LxYaz.jpeg
There are houses about another 100 ft past the trees, but any projection onto my side would be well overhead if you traced a line to their side. Of course, the SKY is over most peoples' houses. This seems like it can't work, I don't see how you could guarantee that a beam didn't find a gap in the trees--but maybe I am overthinking it?
Is there a way to calculate maximum usable image size for a given output power?
Clearly there is some sort of maximum practical range for a projector based on its power and the size of the image and probably the scan rate, too. How can I calculate this? I have no intuition for how wattage translates into real world performance.
Thanks again if you can shed any light on any of this!
Thinking conservatively, the only way I can see to safely use a projector is on an outdoor movie screen via front projection. Using it inside I'd have to rope off half the room and hire security to keep people away from the beam, hah.