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Thread: Can botha a blue laser and a red laser the same wavelength wavelength?

  1. #1
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    Default Can botha a blue laser and a red laser the same wavelength wavelength?

    So this is probably a stupid question, but googled laser forums and this site came up

    Through a casual conversation, someone was talking about a dermatological blue laser and a red laser. During he mentioned the bot had a wavelength of 750nm. From the little I know about visible light, I didn't think that a blue and red laser could both have a 750nm wavelength.
    Now Im just curious. Is it possible?


    thanks!

    L

  2. #2
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    Visible light is from about 670nm to about 390nm. That's deep red to violet. Wavelength is exactly what determines how light effects the cones in a human retina, that we perceive as color.

    Sensitivity to wavelength varies greatly over this range. Green, right in the middle is the most sensitive region, so we see that the best.

    https://en.wikipedia.org/wiki/Color
    Last edited by james; 03-21-2019 at 08:58.
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  3. #3
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    The long-wavelength receptors in the human eye do actually have noticeable sensitivity down to about 410-420nm, so blue light does actually stimulate both the blue- and the red-sensitive receptors, which may be where the confusion comes from. However this doesn't mean that blue light is also red light, that's not true in physical terms or in human perception terms.

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    This is the basis for understanding the difference between violet and purple!

    It also explains why the "color wheel" wraps around, connecting one end of the visible spectrum to the other.

    https://en.wikipedia.org/wiki/Trichromacy

    https://en.wikipedia.org/wiki/Line_of_purples

    James.
    Last edited by james; 03-21-2019 at 10:13.
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  5. #5
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    Quote Originally Posted by james View Post
    This is the basis for understanding the difference between violet and purple!

    It also explains why the "color wheel" wraps around, connecting one end of the visible spectrum to the other.

    https://en.wikipedia.org/wiki/Trichromacy

    https://en.wikipedia.org/wiki/Line_of_purples

    James.
    Thought I'd throw this into the discussion.

    https://photonlexicon.com/forums/sho...-Mastering-RGB
    Last edited by dchammonds; 03-22-2019 at 19:37.
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    So yellow cyan and violet are the peak brightest color by eye to me. Why doesn’t green stick out most?

    looking at your rgb post you posted and the black and white rgb representation.

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    There is no violet in the RGB model. Only tints and shades of magenta.

    Understanding color theory requires the understanding of both additive and subtractive color synthesis.

    Additive color synthesis is about mixing pure hues of light, like the RGB screen you're looking at right now.

    With no light, the screen looks black. As the RGB emitters come on from off to full on the screen gets brighter, approaching white.

    Subractive color synthesis is about pigments that absorb some portion of the spectrum while reflecting others. If you start with white light on a piece of white paper and apply some ink or paint, that will absorb everything in the spectrum except for the color that is reflected, that you see.

    The reason you get purple when you mix red and blue paint (and not magenta) is because red absorbs a lot of blue and blue absorbs a lot of red, so you get a color that is darker than either the red or the blue you started with.

    Yellow is an interesting color. It is a discrete wavelength in the spectrum. It is also the sum of red and green wavelengths, It is also white light minus just the blue and violet regions of the spectrum.

    Cyan is similar to yellow in that it is also a discrete wavelength, the sum of green and blue wavelengths and white light minus red.

    Magenta is a bit odd in that it is not a discrete wavelength. It is the sum of red and blue. It is also the whole spectrum with the middle dropped out.
    Last edited by james; 03-23-2019 at 09:09.
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  8. #8
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    Quote Originally Posted by kecked View Post
    So yellow cyan and violet are the peak brightest color by eye to me. Why doesn’t green stick out most?

    looking at your rgb post you posted and the black and white rgb representation.
    TV color bar pattern shows order of brightness- WYCGMRB

    Click image for larger version. 

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  9. #9
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    It's not s very strong correlation, but it's interesting to think of the RGB model like a speaker system with a woofer, mid-range and tweeter. You need all of them together to hear white noise, pink noise, or the brown note.

    Strangle enough, you need all of them to play the blues.
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