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Thread: Science-y question about light spectrum

  1. #1

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    Science-y question about light spectrum

    So if I want lighting around 400nm on the light spectrum, can I combine lights that have peaks at, for example, 380nm and 420nm and get something "in between"? The lights are addiditive, right?

    THe reason I'm asking is because I've discovered a powerful UV light source for collodion that has a narrow peak at 360nm, while collodion's sensitivity is 380-420nm, so I want to combine my UV light with some blue light to get an "inbetween" nm. Or at least I'm thinking about it.

  2. #2

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    Re: Science-y question about light spectrum

    Look at the graph of the light source output - the output across the light sources entire spectrum. The peak value alone is insufficient information. You need to know how narrow your narrow source really is.

  3. #3

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    Re: Science-y question about light spectrum

    Quote Originally Posted by BrianShaw View Post
    Look at the graph of the light source output - the output across the light sources entire spectrum. The peak value alone is insufficient information. You need to know how narrow your narrow source really is.
    Its pretty narrow.
    High Pressure Mercury Black Light from PHILIPS HPW 125W
    "The UV output is almost monochromatic centred around the 365.5nm line."
    Ironically I see from various graphs that it also has a peak in the red...

  4. #4

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    Re: Science-y question about light spectrum

    ... OK, but with what kind of fall-off? Is it really "sharp cutting" - e.g. no light emissions lower than 365 and none above 366 (for example). How do you know it is 'pretty narrow' if you don't have a plot of its output, and specifically how narrow they are conveying by that description?


    Do you have a notion of how much light you think you need at 380 to 400, or do you just want more than you think this source will provide. if the latter, then the answer is 'sure, light is additive" and you still need to experiment to figure out what you exposure times are in the various lighting conditiions.

  5. #5

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    Re: Science-y question about light spectrum

    Agree with Brian, the part that would contribute to collodion exposure would presumably be the integral over the curve from 380-420. "narrow peak" would suggest a small contribution. So, it's not like using a mired calculator for lighting.

  6. #6

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    Re: Science-y question about light spectrum

    Quote Originally Posted by cyrus View Post
    Ironically I see from various graphs that it also has a peak in the red...
    We're typing over each other at this point... so what does the graph show for the 380 - 420 band? Lots of emission, no emission, or just a lot less than in the peaks?

  7. #7

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    Re: Science-y question about light spectrum

    See this and then scoot down all the way to headings "Black Light/Ultraviolet" and then "Mercury UV Spectrum"

    Seems that a regular, clear high pressure Mercury lamp is my best bet

  8. #8

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    Re: Science-y question about light spectrum

    That's the one I'd start experimenting with.

  9. #9

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    Re: Science-y question about light spectrum

    Danke _ think I'll get a 400 watt bulb and screw around - i have a fixture for 400 wat UV mercury lights but will try with a clear bulb

    Now just have to figure out how many amps that would draw so I dont blow a fuze. . .

  10. #10

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    Re: Science-y question about light spectrum

    As I said, the impact of most of these lighting curves on exposure time requires experimentation. Once that data is known adding more is possible - double the light sources probably halves the exposure time... distance being equal. But it could also build heat...

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