Basic placement and safety questions: should I just forget about a projector?

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.

1. White front projection screens are not created equal. Some front projection screens are designed to reflect on a narrow angle. Some are designed to reflect in a lambertian diffusion. It makes a difference.

2. Rear projection is unlikely to be lambertian.

3. If you're doing imagery on a small screen realize Laserium did stuff with about 500mw on 60 foot domes.

4. The brightness of imagery is entirely about it's complexity. If you do 4 Lissajous loops 50 time a second they're (at least) 10 times brighter than 40 loops.

5. Trees, safe? Maybe, depends on what's beyond them.

front projection on a white wall with the Mobile Beat Mirage is totally safe and won't cause a lot of eye strain.

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Originally Posted by Horseflesh

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.

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First off - LSO course. As I mentioned in your other thread, while certainly worthwhile, you don't need to worry about the LSO course just yet. You CAN in fact, learn plenty about laser safety from this online forum and watching Youtube videos. If you buy the X-Laser Mirage as a matter of fact, there will be a USB key that comes with it with a lot of laser safety information included. I would be willing to bet that of all the people who are out there operating lasers - for home hobby or even commercially, a very, very small percentage have ever taken an LSO class. Like less than a couple percent. I was doing this for a few years before taking the LSO course and still found some of it to be a lot to digest and over my head. I missed passing the first exam by one question and had to take it again a year later but, was far more confident going into the course the second time and aced it. I guess what I'm saying is, for a brand new person just starting to get an interest in lasers who only owns a cat toy laser pointer, it's going to be like trying to drink from a firehose. It's far more than what you need right now.

Secondly... even your basic perceptions are somewhat incorrect. It IS possible to have beams go into the sky. It IS possible to have beams go into a crowd. It IS possible to have your projector and beams below 10 feet. But, there are certain things you need to know and certain steps that need to be taken in order to do some of those things safely. But, as a general rule, you are correct that you should be avoiding those types of things when first starting out.

Of the three laser projectors you are considering, the Mirage is probably the best choice for home use simply because it is the lowest powered. Even some people who have been doing this for years feel that a 2 watt projector like the Unity is too bright for their living room, bedroom or basement. And there are a whole lot of people that will set it on a coffee table and project on a slide projector screen to watch graphics/abstracts. It's quite safe. What you should be concerned about in that sort of scenario are things like... can a child or pet accidentally get between the projector and screen? Is it in a place where someone could inadvertently walk into the room and be walking right into the beams? Is it terminating on a light surface and not risking having a static beam spend a long time hitting a dark drapery and risk smoldering it? Or, anything shiny and metallic that might cause a beam to reflect into someones eyes? Those are more of your primary concerns in a home environment. In addition, some of the safety rules you hear about pertain to operating lasers in a public environment. What you do in the privacy of your own home for non-commercial use is generally your business. Take the 10 foot thing. Very few of us are fortunate enough to have a home where the ceilings are over 10 feet tall. So what in the heck are we to do?? What that refers to is in a public environment, the laser projector and beams should be placed so that neither drop below a height of 3 meters above where a person could reasonably be expected to stand.

So in your home, what you generally would want to do is get the projector ideally above eye level - some put them on top of their refrigerator for example. And take reasonable precautions to make sure unknowing people aren't going to accidentally walk into the beams. If you're watching laser shows, chances are it's going to be adults sitting in chairs and watching them and be instructed to not get up and walk in front of them. If there is a risk of young children who cannot follow that sort of instruction being around, then your safety precaution might be to not watch the laser shows with them around. See? Safety lesson! :-)

As far as front/rear projection on screens in the backyard. My suggestion would be to stick with front projection and maybe put the laser on a stand. As long as the beams are terminating on your screen, you are fine. While I personally love rear screen projection... in a backyard, you're going to have a harder time seeing what hazards might be approaching behind your screen. Generally speaking, any lasers used outdoors should be fully terminated on a solid surface unless you have approval from the FAA for them to be going into airspace. They do NOT consider trees to be an acceptable termination point. Although.... it really is going to come down to the density of the trees and what's behind it. I'd stick with the screen until you learn a bit more. With time and experience you may find certain situations that could be deemed safe for terminating on trees.

I see you are in Bellevue Washington. I know there are several forum members in your area and I'm hoping someone will chime in and maybe offer to get together with you sometime and I'm sure they'd be happy to answer questions for hours. I know there are several in the Portland, Oregon area and they have held several LEM's (laser enthusiast meets). Fun weekends where like minded people get together and watch and play with lasers over a weekend. Jonathan Rehm (platinum on the forum) has organized a few of them and I've flown out for one a few years ago.

Also... your first picture with the lawn chairs and screen would be fine. I'd have the projector in front of the people aimed at the screen. You could get away with a low table provided no kids got to running around in between the projector and screen. Better still would be a tripod or T stand where you could have the laser above the eye level.

Hello Horseflesh,

I started out exactly where you are several years ago. I now have four low(ish)-power lasers in my basement (1W or under) for graphics, abstracts and beam shows. I have two in the back of my basement for graphics/abstracts and lumia, and two in the front for beam shows. While I learned a ton of safety info from this forum and going to SELEM every year since, I did take the LSO course a couple of years ago just to round-out my knowledge on the hobby, even though I never plan to do anything professionally.

And it's funny that Brad responded above, because we were having a similar discussion about setting up my lasers in the basement of my new house, which is a bit smaller than my old house basement.

My new basement, like yours, is 12'x22' and the ceilings are only 7' high! But I still put my abstract/graphics projector (yes, a Mobile Beat Mirage) on the top of a high shelf in the back of the room projecting onto a roll-down movie screen in the front (I'll try to post a photo later). Can people stand up and get in the way of the beams? Absolutely. Do I give clear directions to people not to do that, or exit the room safely? Absolutely. Or what Brad told me so eloquently what he tells his guests, that I made it into a warning sign:

^^ I mean... hell... I've provided guests with a nice recliner, complete with cup holders to watch the lasers. Why would they want to stand up?? *retardo

White wall is fine but it depends on the wattage.. if you are seeing clear after images and its uncomfortable to watch it's not so safe though.. but dropping power and sacrificing color balance as a result can solve this!

Trees is not legally allowed in the USA since you cannot really verify if something makes it through or not.. you need a clear termination point.. then comes the second part to this that the enviroment is also a factor (think of birds and animals living in trees around certain areas).

Thanks a bunch, guys. I have read these replies over a few times and it cleared up a lot. This factoid from @laserist was especially useful to put power levels in real-world context: Laserium did stuff with about 500mw on 60 foot domes

It would be great to connect with another hobbyist around Seattle, too.

It's funny, my wife is pushing for this because she loves to entertain, and wants to design laser shows... I want that too of course, but my being the conservative one when it comes to buying a gadget is role reversal for sure. :)

I am sure I will have more questions eventually but I will try to keep them focused. (no pun intended)

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Originally Posted by Horseflesh

It's funny, my wife is pushing for this because she loves to entertain, and wants to design laser shows...

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You've got a keeper. :)

Perhaps I should start a new thread but this is really closely related so while your attention is here ..

I've got an installation that uses data from lidars to create audio - so the audience is in the live area. I want to add lighting, and two of my favourite ideas are line art, so lasers are easily the most beautiful way to create it.

However, the lit area is where people are. Most obviously, by projecting onto the floor. Unfortunately I can't think of a way of patterning the floor without also making the sources unreasonably dangerous. The next best idea is probably to project onto a a mesh ceiling using lasers at or above floor level and pointed upwards, but it doesn't connect as well with the participants. At worst, I suppose I might use a digital projector but pixels just don't do it for me.

Am I right about the danger of downward-pointing lasers or are beam movement detectors ensuring no static beams sufficient to make that possible ?

firing lasers down into your audience is going to be trouble...

i suggest you use video for immersion and laser on the walls. the audience will probably not figure it out.

Quote:

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Originally Posted by artag

Perhaps I should start a new thread but this is really closely related so while your attention is here ..

I've got an installation that uses data from lidars to create audio - so the audience is in the live area. I want to add lighting, and two of my favourite ideas are line art, so lasers are easily the most beautiful way to create it.

However, the lit area is where people are. Most obviously, by projecting onto the floor. Unfortunately I can't think of a way of patterning the floor without also making the sources unreasonably dangerous. The next best idea is probably to project onto a a mesh ceiling using lasers at or above floor level and pointed upwards, but it doesn't connect as well with the participants. At worst, I suppose I might use a digital projector but pixels just don't do it for me.

Am I right about the danger of downward-pointing lasers or are beam movement detectors ensuring no static beams sufficient to make that possible ?

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