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B Blue light "filters"

  1. Sep 8, 2018 #1
    I have both my iPhone and desktop computer set to a "night light" mode, and obviously my eyes appreciate the warmer colors at night. But what I'm wondering is this: Do they actually work?

    Here's what got me thinking: I have a pair of Elvex glasses rated to block all blue wavelengths, and I have used a simple spectroscope to confirm that they indeed do. No blue light is transmitted. Another cheap pair of yellow glasses I have--while making everything look yellow--still transmit plenty of blue light when I use the spectroscope.

    So, are the LEDs built into our electronic devices not emitting the exact same wavelengths of light at all times, even though they may magnify warm colors more? Perhaps I have a misconception of just what is happening to the light source when my devices go 'warm'.

    Thanks to all.
  2. jcsd
  3. Sep 8, 2018 #2
    I don't get what you're asking exactly, varying the wavelength of light is the same as varying color because the differences in the wavelength of light is what we perceive as color, anything changing the "hue", should change the wavelength.

    Maybe you should read something like this to understand what Apple means by warm/cool color, or color "temperature".


    Or am I misunderstanding your point?
    Last edited: Sep 8, 2018
  4. Sep 9, 2018 #3


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    The color display on your devices actually emit light in three individual colors, namely Red, Green, and Blue. These are the three Primary colors that our eyes have sensors for. Any of the visible colors can be created by various combinations of these primary colors. We see White (or Grey if they are dim) when all three primary colors are of approximately equal intensity.

    For instance that Blue-Grey bar between posts on this site is 23% Red, 32% Green, 45% Blue, but at only half the intensity of White background, thus giving it that Grey shade.

    If you can find a rather strong magnifying glass, look at the various colors on your screen and you will see the individual color sources.

    The nite lite mode on your devices turn down the Blue and Green emitters a bit and turn up the Red emitters a little.

    You can use the Search feature of PF to find many posts on 'color perception'.

    Hope this helps.

  5. Sep 9, 2018 #4
    Sorry for not originally being more clear. Tom, that does help and got me Googling pixels. I didn't know that pixels use phosphors to produce the red, green, and blue wavelengths. That makes sense now. I didn't understand how the computer was controlling the wavelengths themselves (because the LED bulb itself couldn't be controlled in such a way).
  6. Sep 9, 2018 #5


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    that was for the old CRT colour TV/monitors

    Today's LCD TV/monitors work very differently
    As with the old CRT screen there are 3 colours to each pixel Red, Green and Blue and that is where the similarity ends
    In a CRT screen the 3 pixels were phosphor dots and were scanned by 3 electron beams generated by the colour
    guns at the end of the tube.
    The intensity of each of the 3 beams (RGB) caused the phosphor dots to glow accordingly and general a specific overall colour.

    In LCD screens there are basically 3 colour filters per pixel that can be controlled between fully on ... say full Red and fully off = black.

    A white light source is provided by either a white fluorescent tube(s) across the top and or bottom of the screen or by a row(s) of white
    LEDS across the top and or bottom of the screen. The LCD panel controller gets graphics data from the microprocessor to tell it
    how much to turn on or off the 3 RGB pixels to let more or less of the filtered white light through.

    LED displays are yet a different system and your comment above isn't really correct.
    LED displays are often and mainly used for large TV wall type monitors where very high resolution isn't so much of an issue.
    Each pixel is made up (usually) of a single encapsulation that has 3 distinct LEDs inside the encapsulation , one for Red, one for
    Green, and one for Blue

    And again as with the LCD display pixels, the processor, this time, tells the controller how much to turn on each of those 3 LEDs within
    the single pixel encapsulation

  7. Sep 11, 2018 #6
    Amazing technology. Thanks!
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