Math Check - Audience scanning - help?

[demolish50]

Might be in the wrong forum?

So help me out here guys. If I'm going to do some audience scanning of my friends and family I'm going to want 10x MPE. If I ever do it, it will be with close friends/family at my home. Not saying I'm doing it anytime soon as I have a lot to learn and I do understand the legalities and liability involved but putting that aside for a minute please help me understand if I'm understanding what I've read correctly.

So I found some information from ILDA, which I'm sure 90% of you have seen, and I've also seen it here on the forums I think, that provides a "simple" method that involves measuring the irradiance of a static beam at 100 mW/cm2. In theory that gives you 10X MPE for a 1 millisecond pulse when scanning. Give or/take I understand this is not exact.

OK, so I have a Radiant X4. Its detector head I guess you would call it, is 225mm². So that is 2.25cm². So to make things easy, am I'm looking for around 200mW on my sensor, assuming the entire sensor area is full and a static beam at the closest point of my audience?

If this is entirely wrong please explain as if you were talking to a brick

thanks.

[demolish50]

Oh I found this handy tool..good stuff, I'm sure most of you have seen it but just in case.

http://lasersafetyu.kentek.com/easy-...c-web-version/

[norty303]

What is your worst case scenario? E.g. What is the exposure time frame in the event of a failure of the scanners?
In my opinion you should really be using this as your exposure time frame and not a 1ms pulse. Of course, if you have a 1ms or faster scan fail device then you're good
If not, then a failure puts your friends and family in the firing line of 40x MPE

If you want to use the 10x MPE levels then do it based on the 250ms time frame e.g. 25mW/cm2

[demolish50]

So my method is correct? \o/

The speed of a scan fail device is something I had not fully considered, see this is why I ask these things! My eyeballs, and the eyeballs of my friends appreciate the response.

[norty303]

You did what a lot of people do, and that is to just consider a properly running show, and not the worst case scenario.
One of the best things you could for crowd scanning is get a divergent lens like the Pangolin Safetyscan lenses.

[demolish50]

Heh I actually was thinking about picking one up. Probably won't do the set as it will always be the same room. Have not totally figured out how to figure out which one I need yet but I will.

[drm916]

Heh I actually was thinking about picking one up. Probably won't do the set as it will always be the same room. Have not totally figured out how to figure out which one I need yet but I will.

Call pangolin. They will help you pick the right lens.

[demolish50]

I think I got it sorted. I'm going to pickup a -6 diopter lens as soon as they reply to my email and confirm my thoughts. Pretty small room. There is a nice video out there, https://www.youtube.com/watch?v=ooZ1C5gL7FA. Some demo's, looks pretty damn good. When I get mine and play with it I'll let ya know what I think in case anyone reading this has not played with one.

[demolish50]

Nevermind. Doh.

[Pangolin]

When the 10X proposal was being made, experiments by the proposers (Patrick and Greg) were done at the MPE, at 2X the MPE, 3X and so forth. At the MPE the shows look beautiful. As you move upward from there they become damn bright. Effects start leaving after-images. Even 3X the MPE you're really punishing your audience...

The whole "10X proposal" was formulated just to say to regulators "hey, audience scanning has been going on for decades, and done by guys who had no freakin idea how much over the MPE they were (and testing revealed that these idiots were many many more than ten times the MPE)". If you're willing to make two assumptions: 1) That even at 10X the MPE there is still a safety margin (heads-or-tails chance of retinal damage) and 2) *knowing* how far you are over the MPE is much better than not knowing, then you should be willing to accept the 10X proposal.

Personally I thought the regulators would laugh Patrick and Greg out of the room when this was being proposed at a safety conference, because years earlier, when Greg and I did demonstrations at that same safety conference even at 1X the MPE, not even a single regulator would look into the projected shows. Amazingly the regulators actually bought the argument (knowing is better than not knowing, even if you know you're way over).

Note that not all regulators buy this, and it's not official policy. Also note that I personally would never do shows over the MPE -- for the reason that if anyone *claimed* to have eye damage, they'd have a good reason for claiming it, but to me it's more important to have shows that are actually pleasant to view, rather than performed as a form of punishment... But heck, that's just me .

Bill