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Luminous objects definition?

  1. Nov 7, 2011 #1
    My physics teacher was teaching us about light and one of the definitions we have to learn is that of a luminous object. He said the definition is, "Any object that PRODUCES its own light and is seen directly as a result of this light."

    However, I then said that surely his definition is wrong as the Conservation of Energy states that, "Energy cannot be CREATED or destroyed." Therefore in his definition the word produces implies the creation of light, which is a form of energy and therefore would violate the Conservation of Energy.

    Would a more appropriate definition keeping close to his wording be, "Any object which emits light and is seen directly as a result of this light"

  2. jcsd
  3. Nov 7, 2011 #2

    Vanadium 50

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    Are you saying a light bulb produces no light?
  4. Nov 7, 2011 #3


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    We more or less take the conservation of energy for granted in all but relativistic situations.
    In any 'luminous' object there must be some energy transfer going on. This can be chemical-light or electrical - light but this is assumed, I think

    I don't think you need to worry about your teacher's actual wording. It isn't critical, really.
    The only important distinction is between luminous and reflecting objects.
  5. Nov 7, 2011 #4


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    The object is indeed producing light. (The photons did not exist prior to the object becoming luminous).
    What it is not necessarily doing is producing energy.

    It is converting non-luminous forms of energy into photons.

    So, CoE is preseved, even though plenty of photons are being produced.
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