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Thread: 445 requirements compared to 473 for mixing white

  1. #1
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    Default 445 requirements compared to 473 for mixing white

    I was surprised to see in Chroma that I actually needed less mW's of 445 compared to 473nm to get a nice white. I was thinking in the lines of "445 is closer to 405, therefore it should require more mW's of this wavelength". Clearly I was wrong

    ..it makes perfect sense though, since 445nm is more BLUE than 473nm ever was.
    Last edited by skai; 06-07-2010 at 06:01.

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    See how the eye's `blue' sensitivity is higher at 445nm than at 473 nm? So you need less of it for the same amount of stimulus.




    Using 445nm to get white should require a bit more green than when using 473nm because 445nm stimulates the `green' cones less.

  3. #3
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    I know - that's why I wrote it makes perfect sense since 445nm is more blue than 473nm. What surprises me is that 420nm is the peak for the "blue" cones in our eyes. The graph also shows that 405nm is about as "visible" to the eye as 445nm.

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    Yes, you actually need less blue than green power with 445 nm. This is not the case with the other blue wavelengths available for lasers. If you want a nice white you should aim at a ratio of about 1 part 445 nm to 1.2 parts 532 nm and 2 parts 642 nm after optics (assuming the beams are matched). If you are using a longer wavelength red you'll need as much as 10 parts red (at 671 nm).

    One comment on Zoof's diagram is that it shows the absorbance of the different cones. This is different from the eye's response. It is better to look at the color matching functions, because they describe the actual response to different wavelengths. The peak in the blue color matching function is at around 440 nm, which explains why 445 nm is more efficient than 473 nm at shifting the hue towards blue.

    I'm not sure why the absorbance and color matching function peaks are not found at the same wavelength, but I can think of two reasons:

    • Less of the shorter wavelength light reaches the pigment in the cone, because it is absorbed before it gets there.
    • Absorption spectra are on a quantum basis and color matching functions (typically) on an energy basis.

  5. #5
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    With 445 you need less power to get a white, but what about the brightness of the separate blue color only.

    Chroma shows:
    1W of 445nm gives 28 luminous flux
    1W of 473nm gives 70 luminous flux

  6. #6
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    Quote Originally Posted by mccarrot View Post
    With 445 you need less power to get a white, but what about the brightness of the separate blue color only.

    Chroma shows:
    1W of 445nm gives 28 luminous flux
    1W of 473nm gives 70 luminous flux
    1W of 445nm is about as much as a movie and a nice dinner.

    1W of 473nm is, kind of, priceless.

    Nuff said.

  7. #7
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    Quote Originally Posted by tocket View Post
    One comment on Zoof's diagram is that it shows the absorbance of the different cones. This is different from the eye's response. It is better to look at the color matching functions, because they describe the actual response to different wavelengths. The peak in the blue color matching function is at around 440 nm, which explains why 445 nm is more efficient than 473 nm at shifting the hue towards blue.

    I'm not sure why the absorbance and color matching function peaks are not found at the same wavelength, but I can think of two reasons:
    You are right, this is absorbance. There are a number of different graphs out there, and they graphs show the distinct peaks at roughly the same places. This is not my field, but from what I read there is not a direct way to measure the perceived brightness of light, just absorbance and chemical (?) response of the cones.

    There is also a graph that corresponds to the CIE model of the eye's response, that should be the accepted diagram (from matlab ;-) ) and is the basis for you chroma calculations, right? :



    anyway, human color vision is a fascinating field.

  8. #8
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    Graphs - Giraffes........

    Describe the colour White?

    We ALL see colours different!
    We ALL see white different!

    As I have said before, I have 1W of 532, turned down in my SW to around 500mW, 800mW of 635 and 270mW of 473 after scanset and dichro's and it looks perfectly white to me.

    Stick them into Chroma!
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    Continuously in Awe! of (H)Al, the Photonlexicon Font of Complete Knowledge - The (H)Al'PL Database of complete puss that no one needs to know or ever trusts as he ain't really got a Scooby doo about now't!

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    no-no-no-no-no the gap between theory and practice is sacred - it should not be closed! :-)

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    @ smog
    Do you blame speaker builders for trying to approach a flat phase and frequency response and using the latest insights in acoustics ?

    We all experience music differently, so why bother looking at a frequency response of a speaker in the first place? Surely people should trust their eyes and ears when purchasing a new pair of speakers, and not look at graphs. But you can not deny that taste is subjective.

    If you say that color-theory is wrong, propose a new theory, make (more) accurate predictions, design a experiment, falsify predictions. Until that time modern color theory is right, and your personal perception is deviant.

    People who use chroma want to approach a D65 white because it's generally accepted as neutral white, with a huge heap of biological, empirical, statistical, neural, photo-chemical proof to back it up.
    Nobody is forcing you to perceive D65 white, as your white though.


    and it looks perfectly white to me
    In what frame of reference ? Have you compared it side by side with a ray of sunlight ?

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