Is it possible to have a bright enough light to project an image onto a flame?
Why or why not?
I would say no.
A flame is not a reflective surface–it is constantly moving gas. Could you project an image onto a tornado? Same thing.
Why couldn’t you project an image on a tornado? It’s mostly made up of solid particulate matter, so with a strong enough light source (and assuming it’s fairly dark outside), you should be able to project something. But it’ll be fuzzy and chaotic as hell.
As far a flame, I wouldn’t think so, like Aeschines said, it doesn’t have any reflective qualities.
A flame is just a mixture of hot gas and dust. If it’s mostly gas, there won’t be much light scattering, and not much of a reflection. If there’s dust (unburned carbon, minerals, buckyballs etc.) in the flame, it’ll scatter light, and you’ll see it reflected, just as you can see a laser beam scattered off smoke.
I’m not sure that a flame has a surface that is well defined enough to show and image. Hot gas and particles rise from a fire and some of the gas and particles are hot enough to emit light. However I think a light projected into a flame would be like a searchlight into a dusty atmosphere. It would just be a shaft of scattered light.
I presume the presence of dust is what makes some flames visible while others (like burning hydrogen or methanol) aren’t. So light should be reflected by a visible flame, it would just have to be damn bright to be observable above the light emitted by the heating of the dust particles themselves - even brighter if projected on a thin sheet of flame so as to get a sharp focused image
thanks for your answers
A while back, in the audiophile world, there was some work with using a gas flame as a loudspeaker. Specifically, researchers passed a current through a flame, and they found it made an accurate tweeter (high frequency speaker.) The concept never caught on. I wonder why. “My God, man, your speakers are on fire! Gimme the punchbowl !”
In order for what you’re suggesting to work, fire would have to become brighter in very bright light. But in very bright light, fire becomes invisible.
Flame is not completely transparent: If it were, it could not emit light of its own. And I don’t know what the albedo of a flame is, but I’m sure it’s not exactly zero. Given that, I don’t see why it wouldn’t be possible, given a bright enough projector, to project a visible image onto a flame, just as one might project an image onto any other surface. However, I suspect that such a projector would need to be so bright as to be impractical.
I thought the difference was the temperature of the flame: a hydrogen or methanol flame would still produce light, but it’d be either infrared or ultraviolet and thus invisible to the naked eye.
Well, I tried a laser pointer light on a gas (butane) flame, and it passed through the flame (both the bright yellow part and the clear, bluish base) seemingly undistorted and invisibly. FWIW.
I disagree. I recently saw a very early Technicolor film in which there were candles in the scene. I was surprised to notice that the candle flames were a relatively deep yellow, as opposed to white, which is how flames appear on modern, faster film. Obviously the Technicolor film required huge amounts of light to expose.
I think it would be possible to project an image on a flame, although in addition to lots of light, it might take some fiddling with fuel sources to get the best results. At theme parks and water shows, movie and laser images are projected on sheets of sprayed water. I think a similar arrangement, projecting on a sheet of flame might work. Lasers would be an obvious starting point.
Has anyone thought of doing a simple experiment with a candle and a laser pointer?
D’oh!
Bright lights may wash out the light from a flame, but in this case we’re only interested in light reflected off a fire, not the light the fire emits.
The analogy to sheets of water mist may not be very good. I suspect fire is far more transparent than mist. It looks opaque because its glow blots out the image of things behind it.
Depending on how early a Technicolor film this was, this may not be a valid comparison. The earliest Technicolor films, using the so called “two strip” method, were actually filmed on regular B&W film stock, using a prism to split the light into the red portion of the spectrum, filmed on one strip of film, and the blue/green portion of the spectrum, filmed simultaneously on another strip. How it was projected depends on the specific process. However, this heavily accented the red/orange/yellow colors, which is likely responsible for the deep yellow of the candles. You are correct, however, that true Technicolor (the “three strip” method) required a great deal of light to expose properly. Technicolor demanded a representative technician be on set at all times during filming; it was said that their main job was to fix the cameras and stand around saying that the scene needed more light.
As for the flame projection, the easiest way to test this would be to find an acetylene based gas chromatograph (doesn’t everyone have one in their basement?), which delivers an intense, rectangular and relatively thin flame that remains constant and does not flicker. I suspect that in total darkness, you would be able to see a laser pointer on the flame.
If it interest you, the Technicolor info can be found here.
Sorry, I should have clarified. It was a three-strip film.
From that site:
NOT!
We were both typing at the same time, I just hit the “Submit Reply” button a minute or two before you.
(And, I have a fast connection 
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