So, presumably "bright enough to burn the image on your retina" is lower than the threshold for permanent eye damage? If it's not a lot lower, it's scary to think that the movie-goers had no idea it was going to happen and a miscalibration of the mechanism could've caused lifelong eye problems.
"burning" is a bit of an exaggeration, I think. It's just overstimulating your retina cells, so they sort of take a rest. It doesn't take much energy - glance at a 40-watt unfrosted bulb, then close your eyes, and you'll see an afterimage.
From the video it appears they are using 2 (or more) Pro-7b 1200 units, each delivering 1200 Joules of energy per flash. That's enough to light a 40-watt bulb for a full minute, and the lighting efficiency is considerably higher.
BTW, the Pro-7b is a rather small battery-powered flash unit. The bigger mains-powered ones pack twice the energy (and have much shorter cycle times).
Your 40-watt bulb has to be fairly close in proximity in order for the light to make things more visible. And since movie screens are so big, you have to be fairly far away in order to see the whole picture.
The energy output from light follows the inverse-square law, so double the distance is 4 times less bright, and quadruple the distance is 16 times less bright.
So although the energy output is higher, it's probably not as bad as you think it is.
I never meant to imply it was bad. Looking directly at a flash bulb like that from typical movie-viewing distance is perfectly harmless. I would not want to look at one up close, however.
Yes, but that energy was also mostly masked by the "BMW" stencil and then also apparently filtered through the projection screen. The amount of light actually hitting the viewers' eyes was much much less than the actual output of the strobe units.
My understanding is that visible light is very safe because it takes a long time for damage to happen and you naturally protect yourself. Of course "burning an image" really just means causing your eye to perceive an after image.
Natural visible light, yes; even somewhat concentrated reflected sunlight will take more than a blink to harm you. Visible light in general, hell no it's not safe. For goodness' sake, be careful with your lasers. And beat the everloving crap out of anyone being casual with those damned bright green lasers, which are most emphatically not toys.
I'm not saying that this theater flashing stunt was dangerous, I doubt it was anywhere near dangerous, I'm saying the idea that all visible light is safe can get you blind.
Right yeah, absolutely. What I really meant was white light of a fairly broad spectrum, hopefully no one read my comment and thought it applied to visible spectrum laser light.
They used off-the-shelf studio flashes. There really isn't a whole lot of "calibration" nor chance for "miscalibration".
The nature of these units prevents them from outputting a bright light for more than a few milliseconds. Any catastrophic failure would have most likely resulted in the flash bulbs exploding with sparks and flying glass shielded by the projection screen. Had that happened it would have only enhanced the effect.
Those flashes work by charging a capacitor bank to 1kV, then discharging it through the flash bulb. The components are selected to maximise the current during the discharge. In other words, they are designed to output as much power as possible. Any kind of failure can only reduce the power and/or energy from the intended.
I would guess the comparison to the sun is what's really driving your concern. IIRC, the real danger of the sun is the invisible parts of the spectrum- the danger of what direct exposure to the sun's UV rays can do to your retina.
(Obviously a light bulb flash does not irradiate you with nearly as much UV as the sun)
Yeah the article is annoyed that this would never fly in the us, but honestly this is exactly one of the times where a lawsuit is appropriate - and not only against the movie theater, but bwm too.
