The interaction between light and matter may lead to the following effects:
1. Transmission without interaction;
2. Reflection without absorption effects;
3. Transmission and/or reflection, where the light changes the energetic state
of the sample; and
4. Transmission and/or reflection with light scattering effects at the sample.
The law of conservation of energy states that the light transmitted throughany sample, plus the sum of reflections by the sample, results in the factor 1 of the energy introduced.
The law does not account for the fact that transmitted light may be refracted, diffracted, or scattered by the sample. It also does not consider that absorbed energies may appear in the beam as luminescent signals. Similar effects can modify the reflected light beam. If one precisely measures both the transmission and reflection of a sample, the sum may be <1, having no error in measurement; however, if the result turns out to be <1, one would have a perpetuum mobile (perpetual motion machine).
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