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    hi can someone tell me about LEDs and their nature of the colours that they emit? also how would you see the light intensity level of LEDs? i was reading the book and it barely says anything about them.
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    Think about excitation energies to raise electrons to a higher energy band.

    Now think about a diode semiconductor junction.

    Where does the energy come from to raise electrons to a higher energy shell in and LED?

    Is the electron configuration stable in that higher energy state?

    What do these 'excited' electrons want to do?

    When they revert to a more stable condition, in what new form is the previously gained energy given off?

    What can you say about the wavelength of the photons as the electrons fall to a lower energy state?
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    (Original post by cooldudeman)
    hi can someone tell me about LEDs and their nature of the colours that they emit? also how would you see the light intensity level of LEDs? i was reading the book and it barely says anything about them.
    Basically its a semi-conductor which, when switched on increases electron energy level. The electrons later release energy in the form of photons. The colour of the light is dependent on the energy of the photon as E=hf.
    Intensity is the number of photons striking a surface in a given time period.
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    (Original post by joostan)
    Many LEDs have plastic casings to change the colour.
    Basically its a semi-conductor which, when switched on increases electron energy level. The electrons later release energy in the form of photons. The colour of the light is dependent on the energy of the photon as E=hf.
    Intensity is the number of photons striking a surface in a given time period.
    oh so the greater the E=hf, the greater the intensity? so is low intensity=red and what if it had higher intensity? what colour would it change to? is white the greatest intensity?
    also how would you actually measure the no. of photons striking a surface? like some sort of 'photon sensor'?
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    (Original post by joostan)
    Many LEDs have plastic casings to change the colour.
    Absolute tosh.

    'White light LED's' are a mixture of yellow and blue to mix light that appears white or a mixture of the three primary colours.

    Trying to filter out colours from that 'faux white light' using the casings is a very inefficient way of generating an LED colour.
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    (Original post by cooldudeman)
    oh so the greater the E=hf, the greater the intensity? so is low intensity=red and what if it had higher intensity? what colour would it change to? is white the greatest intensity?
    also how would you actually measure the no. of photons striking a surface? like some sort of 'photon sensor'?
    Not quite.

    Rearrange the equation:

    f=E/h

    Remember that we are talking about permitted energy bands since electrons can only occupy predefined bands for a given element.
    So if an electron drops from a higher energy state it gives up the difference in energy between bands.

    Hence the colour is determined by the energy bands.

    The intensity is a function of how many electrons drop in a given time.
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    (Original post by uberteknik)
    Not quite.

    Rearrange the equation:

    f=E/h

    Remember that we are talking about permitted energy bands since electrons can only occupy predefined bands for a given element.
    So if an electron drops from a higher energy state it gives up the difference in energy between bands.

    Hence the colour is determined by the energy bands.

    The intensity is a function of how many electrons drop in a given time.
    ok so im guessing you're talking about the de-excitation of the electron. then they just emit the light.
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    (Original post by cooldudeman)
    ok so im guessing you're talking about the de-excitation of the electron. then they just emit the light.
    Yes.
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    (Original post by uberteknik)
    Absolute tosh.

    'White light LED's' are a mixture of yellow and blue to mix light that appears white or a mixture of the three primary colours.

    Trying to filter out colours from that 'faux white light' using the casings is a very inefficient way of generating an LED colour.
    My mistake, although surely the selection of shades requires casings, I extrapolated from fluorescent lamps.
    And for the record (though not in this case) just because something is inefficient doesn't necessarily mean it isn't done.
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    (Original post by joostan)
    And for the record (though not in this case) just because something is inefficient doesn't necessarily mean it isn't done.
    Well OK. lol.

    Just that the light emitted by LED's is very monochromatic so the colour filter would be pretty irrelevant as it would then have to block the very wavelength generated in the first place!
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    (Original post by joostan)
    Many LEDs have plastic casings to change the colour.
    It's actually the semi-conductor used which defines what colour light is emitted. The plastic case is only to represent the colour when the power is switched off. Different semi-conductors produce different colours of light.

    It's like a hot tap being coloured red even though the water is still clear! The plastic is there to represent the colour. It might help to normalise the colour a little, but a red LED would be red with a clear coating. Most high intensity blue ones are clear coated too.
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    (Original post by SillyEddy)
    It's actually the semi-conductor used which defines what colour light is emitted. The plastic case is only to represent the colour when the power is switched off. Different semi-conductors produce different colours of light.

    It's like a hot tap being coloured red even though the water is still clear! The plastic is there to represent the colour. It might help to normalise the colour a little, but a red LED would be red with a clear coating. Most high intensity blue ones are clear coated too.
    Ahh I get what you're saying
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    (Original post by joostan)
    Ahh I get what you're saying
    so what colour means like the highest/lowest intensity?

    if its red, is that low?
 
 
 
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