Page 1 of 2 12 LastLast
Results 1 to 10 of 17

Thread: "photopic-scotopic vision"

  1. #1
    Join Date
    Jan 2007
    Location
    Florida
    Posts
    4,382

    Default "photopic-scotopic vision"

    I've run across this a couple of times now--can anybody verify this?

    This chart shows the eye's sensitivity to different wavelengths (colors). There are two curves, one for daytime vision and one for night vision.
    As you can see, the maximum sensitivity for both curves is in the green. Blue and red light of the same power appear less than half as bright to the eye.
    Attached Thumbnails Attached Thumbnails photopic-scotopic-vision.gif  


  2. #2
    Join Date
    Dec 2006
    Location
    Pflugerville, TX, USA
    Posts
    1,977

    Default

    That chart shows eye sensitivity vs wavelengths for a fixed power. But, is there a chart that shows eye sensitivity vs power for given wavelengths?

    For example, I don't think that a 5mw laser green looks 1/2 as bright as a 10mw green laser or 1/10 as bright as a 50mw laser. So, based on that, I am not so certain that you can use the sensitivity chart to determine what power red and green you need to make them equally as bright. I'd be surprised if you could even tell the difference in brightness between a 1W red and 1W green (just a guess).

    In other words, what we really need is a chart or something else that can tell us what power of a color is equal in brightness to some power of some other color.

  3. #3
    Join Date
    Jan 2007
    Location
    Florida
    Posts
    4,382

    Default

    Well the chart is showing that the eye has different sensitivities to different wavelengths in the daytime vs nighttime (a shift towards the green-blue and away from the red. Most laser shows are done in low-light environments making the dotted graph the one to refer to for us laser people as far as eye sensitivity. I just didnt know if this has been verified scientifically. As far as high powers go, yeah I guess they'd all be bright

  4. #4
    Join Date
    Jan 2007
    Location
    Florida
    Posts
    4,382

    Default

    Here is one standard chart that just shows eye sensitivity.
    There's another (I cant find it-I believe its somewhere on Sams FAQ)with numerical data showing multipliers that you would have to calculate in order to determine power levels and wavelength for equal visability. Its definitely not linear, though -50mw is not twice as bright as 25...
    Attached Thumbnails Attached Thumbnails eye color senitivity.JPG  


  5. #5
    Join Date
    Jan 2007
    Location
    Florida
    Posts
    4,382

    Default

    Heres the numerical chart:
    I dont know about this tho..according to this you would need 14.5 660nm (x) power lasers to only (1) 532mn of the same (x) power
    Attached Thumbnails Attached Thumbnails wavelength.jpeg  

    Last edited by steve-o; 04-12-2007 at 10:51.

  6. #6
    Join Date
    Dec 2006
    Location
    Pflugerville, TX, USA
    Posts
    1,977

    Default

    The numerical chart and the graph say the same thing. But they only account for the same power level. It isn't saying you need 14.5x red power to equal green power. It is saying that if green and red are the same power that green will be 14.5 times brighter. Those are too very different cases.

  7. #7
    Join Date
    Jan 2007
    Location
    Florida
    Posts
    4,382

    Default

    I don't know.
    My original question was, though, the night-time spectral shift. True or not?

  8. #8
    Join Date
    Dec 2006
    Location
    Pflugerville, TX, USA
    Posts
    1,977

    Default

    Oh yea, the night time shift is definitely true.

  9. #9
    Join Date
    Jan 2007
    Location
    Florida
    Posts
    4,382

    Default

    Ok if the eye sensitivity is .061 for 660nm and .885 for 532 "at the same power level" what math would you use to figure the power of the red to match the apparent brightness of the green? I'm guessing a non-linear logorithmic scale, but how would that apply to apparent brightness of the linear specific wavelengths?

  10. #10
    Join Date
    Dec 2006
    Location
    Pflugerville, TX, USA
    Posts
    1,977

    Default

    Beats me, to be honest. But I would like to know.

    Perhaps some experimenting is in order. Is there anyone on here with access to a power meter and lasers of various wavelengths that can be power adjusted?

    I would love for a chart to be made up like this:

    532nm 405 nm 635nm 650nm 660nm etc
    5mw xmw
    10mw
    20mw
    ...
    100mw
    etc

    Basically it would involve setting the green to various power levels then adjusting the others to match intensity as best as could tell from looking at it.

    Any takers? If you do it we could name the chart after you and you'd be famous forever amongst laser show people.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •