Last night, I was at a concert and the singer’s microphone stand cast two shadows on him. One was red and one was blue. I always thought shadows were created by an object blocking light. So shouldn’t shadows always be black?
I got this response:
If the shadow is blocking ALL light, yes; but clever lighting arrangements can set up so that there is an additional source of light behind the singer, and the shadow can be colored.
There was definitely no source of light behind the singer. And he and the band all threw colored shadows on the wall behind the stage, though not as distinct because the wall was dark and the singer was wearing a light T-shirt.
One way is to light the stage with a red light from one side and blue light from the light. Where they meet, the lights add up to white. Where one light is blocked, it is only illuminated by the other light and appears colored.
(OK, strictly speaking, red and blue don’t add up to white. You could use cyan and magenta, or red and green and blue.)
It sounds like there were two lights shining on the singer from in front of him. One red and one blue, shining from slightly different angles from the front.
With two sources of light, he’ll cast two shadows - each shadow is where light from one of the two lights is blocked. One shadow will be where the light from the red light is blocked. This shadow will appear blue because the wall there will be illuminated only by the blue light and not the red one. The other shadow will appear red, because the blue light is blocked in that region, but not the red.
Years ago, I made a little gimmick for projecting “3D” shadows, using a red-filtered light and a blue-filtered light set slightly apart. The parallax was reversed, so when you stood facing the wall, your shadow appeared to be standing “behind” the wall, and would reach out toward you if you reached out to it. (If you were wearing 3D glasses, obviously.) Went over well at house parties – but then, everyone was high.
Thank you. But, when I said I wanted blueprints and schematics I was being literal.
I understand the concept. But, need help on how far apart to place the lights, how far the lights should be from the wall shadows are being cast on, the proper angle of the lights, how to properly match bulb colors so that the glasses will work, etc.
how far apart to place the lights: same as eye separation is recommended. Wider separation will exaggerate the 3-d effect, but your brain will interpret the shadows as smaller.
how far the lights should be from the wall shadows are being cast on: some brief experimentation should reveal this. Start with the opposite wall.
the proper angle of the lights: again, brief experimentation. Start with parallel. Different angles will produce different depth effects.
how to properly match bulb colors so that the glasses will work: don’t worry about colored bulbs. Use the glasses as filters. If you’re using slide projectors, secure one of the colors over each lens somehow. If you don’t mind destroying a pair of glasses, mount the colored lenses as slides (if they can resist the heat). You could also use clear glass bulbs - dimmer but should work. Get two small boxes, cut a small hole in each, tape the colored lenses over the holes, place over bulbs. Be careful of those boxes - possible fire hazard.
It may be somewhat difficult to keep the two light sources horizontally level. If they aren’t, the images won’t coincide properly and could cause eyestrain.
I never made any plans – just cobbled a couple of halogen bulbs onto a sliding track stuck onto a tripod, with filters over them. Worked okay, but I found that it had to be too close to the wall to be practical. I later made another attempt using a single light source and salvaged optics from an old slide projector, with one side filtered blue & the other side red. The shadows weren’t as sharp, but it had the advantage of working from the other side of the room.
It’s pretty simple – a little experimenting will give you what you want, there’s not really a way to go wrong. (In fact, the first time I saw this effect was accidentally, when a friend had lit their bathroom with a combination of red & blue bulbs in one fixture over the sink-- a little rearranging of the bulbs was all it took to get a workable effect-- moving the lights or the wall was out of the question…)
shadows can only occur where there is a light source or sources…these could ‘affect’ the colour sensitivity of the eye to make the apparent area of shadow coloured, like an aura.?
