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Visible illumination in daylight

  • 07-08-2008 3:26pm
    #1
    davidclayton
    Registered Users, Registered Users 2 Posts: 1,218 ✭✭✭


    Are there some colours of light that are more visible in daylight than others?
    For example, if I was outside during the day and I illuminated several LEDs of the same brightness, but each had a different colour, which one would be the most visible?

    ...random question, i know... :confused:


Comments

  • #2
    Professor_Fink
    Registered Users, Registered Users 2 Posts: 861 ✭✭✭Professor_Fink


    davidclayton wrote: »
    Are there some colours of light that are more visible in daylight than others?

    Yes.
    davidclayton wrote: »
    For example, if I was outside during the day and I illuminated several LEDs of the same brightness, but each had a different colour, which one would be the most visible?

    This is a more complicated question. The sun's spectrum peaks at about 500 nm which is green. Since the light from the LED has to compete with sun light to be visible light closest to green should be hardest to see, with the extremes (red and violet) appearing brighter, even if they have the same luminosity.

    Things are a little more complicated, however, by how our eye works. We have three kinds of receptors (often associated with red (L), green (M) and blue (S) although their peak performance is a litte different). The peak frequencies are at roughly (S) 420–440 nm, (M) 534–545 nm and (L)564–580 nm.

    We would expect (M) to be swamped by the natural light, with (M) and (L) less effected. As a result, I would expect LEDs in these ranges (420-440 and 564-580) to appear the brightest. These correspond to violet and yellow respectively.

    Maybe a biologist or physiologist can set me right!


  • #3
    davidclayton
    Registered Users, Registered Users 2 Posts: 1,218 ✭✭✭davidclayton


    interesting. thanks for your input.


  • #4
    Red Hand
    Registered Users, Registered Users 2 Posts: 4,986 ✭✭✭Red Hand


    Would it have to do with the rods and cones in our eyes? Rods, if I remember, can distinguish light whereas the cones can distinguish colour?


  • #5
    Professor_Fink
    Registered Users, Registered Users 2 Posts: 861 ✭✭✭Professor_Fink


    Jeremiah 16:1 wrote: »
    Would it have to do with the rods and cones in our eyes? Rods, if I remember, can distinguish light whereas the cones can distinguish colour?

    Basically, yes, but there are several different kinds of colour receptors (cones). Each on its own cannot distinguish colour, but is more or less sensitive at different wavelenghts. By comparing the response from the three we get the illusion of colour.


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