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Would it be possible to get a "white" lighthing of a subject by using 3 different lasers (R, G and B)

If so, which wavelengths and proportions should be used ?

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Why use lasers? Mixing R G and B LEDs can look fairly good. LEDs have a much wider spectrum than a laser. Though the calibration will be tricky since as @Michael Nielsen said, humans and cameras will see the mix differently. –  Phil Jan 11 '13 at 17:01
    
To light the subjects with coherent, monochromatic light. –  Skippy Fastol Jan 11 '13 at 17:03
    
Are you making a color hologram? –  Phil Jan 11 '13 at 17:06
    
@Phil: I confess I am not. –  Skippy Fastol Jan 11 '13 at 17:09
    
It would be nice if I knew more about what you want to achieve. Here is a short answer assuming for some reason you need monochromatic, coherent light to take a photo using a common digital camera. If this is the case, don't worry about the color balance. You will likely need all the photons your lasers can make. Take a picture with a white subject and set the ratio of each channel later. –  Phil Jan 11 '13 at 17:16
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2 Answers

You can get white LED lights that like monitors do actually create white from combinations of very narrow bands of R, G and B light - we perceive it as white of a certain "Kelvin" balance, but if you use a spectrometer, you will see spikes.

http://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/chap20/chap20.htm

The same goes for fluorescent lights:

http://web.ncf.ca/jim/misc/cfl/

Compared to old light bulbs and halogen the benefit is that they don't emit IR light, ie. waste so much power on heat, which is why we see them as brighter at lower watts. However, cameras will see them as really dim, because the integration of the sensor's sensitivity curve times the emitting source curve ends up rather small, with all those spikes.

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I love the first link. Many thanks. –  Skippy Fastol Jan 11 '13 at 16:35
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No. "White" light contains all wavelengths of light - the Kelvin temperature just affects the proportions of each wavelength. Three lasers will have just three specific wavelengths so can't possibly reproduce the full spectrum of light that is in white light.

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Could you please expand a little bit more ? How would a person lit with equal proportions of R, G and B lasers look different from it she were lit with a white light ? Would the CCD sensor of a camera be able to "feel" the difference ? If that is not possible, then how are monitors able to display color images from only red, green and white pixels ? –  Skippy Fastol Jan 11 '13 at 16:00
    
Maybe this will help: photo.stackexchange.com/questions/10385/… –  David Rouse Jan 11 '13 at 16:15
    
@David Rouse: Thank you –  Skippy Fastol Jan 11 '13 at 16:34
    
What if your lasers very closely matched the primaries used by the R, G, B filters in your camera? –  mattdm Jan 11 '13 at 17:20
    
@mattdm: how may I know about those filter's frequencies ? –  Skippy Fastol Jan 14 '13 at 17:21
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