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Thread: Wavelength Errors?

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    ATO Member HarryChiling's Avatar
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    Wavelength Errors?

    The reference wavelength we use is 589nm, now I have worked in offices that have had flourescent lighting. Flourescnet lighting has a wavelength of 546nm, since 45nm is enough to create a 0.25 diopter difference in power, does that mean these offices are sending out bunk scripts almost daily?
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    Objection! OptiBoard Gold Supporter shanbaum's Avatar
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    Quote Originally Posted by HarryChiling View Post
    The reference wavelength we use is 589nm, now I have worked in offices that have had flourescent lighting. Flourescnet lighting has a wavelength of 546nm, since 45nm is enough to create a 0.25 diopter difference in power, does that mean these offices are sending out bunk scripts almost daily?
    I don't think the ambient lighting in the office matters. What does matter is the color temperature of the light sources (together with any filtration) in the refractionist's projector used to determine the Rx, and the lensmeter used to measure the finished product.

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    OptiBoard Professional jrumbaug's Avatar
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    I understand that the 2 light sources have different refenece points. But the charts are traditionally black letters on a white blackground. The red green chart is used to detect a .12 diop refraction difference. If you you were talking about charts with black letters on a red baclground, vs black letters on a green background, I would say, now we have an issue. But white backgrounds illuminated with different type of "white" light, I am hard pressed to believe there is a difference. But it could be a good research idea or the basis of a doctorate.

    Jim Rumbaugh

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    Are not the wavelengths of light broken up and changed by whatever it reflects off of? Isn't green a specific wave lenght whether one see it with a lasier, in sunlight, flouresent light or incandesent light, or the reflected glow from phosphorus?

    Chip

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    OptiBoard Professional jrumbaug's Avatar
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    Quote Originally Posted by chip anderson View Post
    Are not the wavelengths of light broken up and changed by whatever it reflects off of? Isn't green a specific wave lenght whether one see it with a lasier, in sunlight, flouresent light or incandesent light, or the reflected glow from phosphorus?

    Chip
    I agree that green light is the same regardless of the source. But I am not sure what your point is??? It is true that red light is bent diferently than green light, but I have not heard of different types of 'white' light showing a significant difference that would effect a refraction.

    and just to confuse the matter. Some colors can be misleading. There is yellow light and orange light, but when we see yellow and orange via a TV set, we are seeing combinations of red, green, and blue light.

    Jim Rumbaugh

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    Jim:
    My point was: Once it is reflected (except from a mirror) it doesn't matter much what the source was origionally.

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    Objection! OptiBoard Gold Supporter shanbaum's Avatar
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    Quote Originally Posted by chip anderson View Post
    Jim:
    My point was: Once it is reflected (except from a mirror) it doesn't matter much what the source was origionally.
    Sure it does. The color of the reflected light will be the same as that of the source, all other things being equal. If the source is burning sodium, it will be yellow; if it's burning mercury, it will be green.

    It may be possible to produce the same color from a variety of sources (if that's what your saying).

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    Shanebaum:

    Unless fail to remember (there is a lot I fail to remember) the reason we see color is that is the color reflected off an object. If I see green, then all other colors are absorbed by the object. White light is made up of all colors but we only see what is reflected back to the eye. Unless we look directly at the light source or see it reflected from a mirror. With the exception of some pre-filtered light and a few flouresing objects, if the light comes from a sodium light, a flourescent light, incandescent light, I still see only the wavelength for green off an object that reflects green and absorbs other colors.
    Exception being white objects returning pre-reflected or pre-filtered light.

    Chip

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    Objection! OptiBoard Gold Supporter shanbaum's Avatar
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    I figured we wuz talkin' bout projector screens or mirrors, which, I spect, would 'flect all colors uniformarily.

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    Master OptiBoarder Darryl Meister's Avatar
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    I agree that green light is the same regardless of the source. But I am not sure what your point is??? It is true that red light is bent diferently than green light, but I have not heard of different types of 'white' light showing a significant difference that would effect a refraction.
    As Robert pointed out, "white" is dependent upon the original source. For luminous objects that produce their illumination through incandescence, such as a typical light bulb, the "color" of the light will depend upon the temperature of the source. Light produced by lower temperatures -- such as an incandescent light bulb (2800 deg K) -- produce more of a "reddish" white, while light produced by higher temperatures -- including the sun (6500 deg K) -- produce more of a "bluish" white. This is known as the correlated color temperature, and the various "colors" of "white" vary as a function of the temperature of incandescent sources, following a curve known as a "Planckian locus" on a color chart. This is the perceived color of a black body radiator as its temperature is increased.

    A white surface illuminated by another object, such as a sheet of paper under a light, doesn't actually produce any "white light"; it simply reflects all colors from the original light source uniformly (yet diffusely). If, for instance, you were looking at that "white" sheet of paper under a red light, it would of course appear red. Consequently, a sheet of paper -- or an eye chart -- under a color-corrected fluorescent light will have a different luminance profile than that same sheet of paper under a typical incandescent light bulb.

    That said, the actual visual differences produced between different "white" light sources during an ocular refraction are probably negligible. For optical measurements of lenses with relatively low Abbe values, on the other hand, the narrow-spectrum light sources typical of focimeters can produce significant differences in power readings because of dispersion effects.
    Darryl J. Meister, ABOM

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    ATO Member HarryChiling's Avatar
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    Quote Originally Posted by Darryl Meister View Post
    As Robert pointed out, "white" is dependent upon the original source. For luminous objects that produce their illumination through incandescence, such as a typical light bulb, the "color" of the light will depend upon the temperature of the source. Light produced by lower temperatures -- such as an incandescent light bulb (2800 deg K) -- produce more of a "reddish" white, while light produced by higher temperatures -- including the sun (6500 deg K) -- produce more of a "bluish" white. This is known as the correlated color temperature, and the various "colors" of "white" vary as a function of the temperature of incandescent sources, following a curve known as a "Planckian locus" on a color chart. This is the perceived color of a black body radiator as its temperature is increased.

    A white surface illuminated by another object, such as a sheet of paper under a light, doesn't actually produce any "white light"; it simply reflects all colors from the original light source uniformly (yet diffusely). If, for instance, you were looking at that "white" sheet of paper under a red light, it would of course appear red. Consequently, a sheet of paper -- or an eye chart -- under a color-corrected fluorescent light will have a different luminance profile than that same sheet of paper under a typical incandescent light bulb.

    That said, the actual visual differences produced between different "white" light sources during an ocular refraction are probably negligible. For optical measurements of lenses with relatively low Abbe values, on the other hand, the narrow-spectrum light sources typical of focimeters can produce significant differences in power readings because of dispersion effects.
    Awesome that's what I was lookign for. It was more a curiosity than anything else. Thanks.
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