The light source emit ultraviolet rays and propagate in the medium. Ultraviolet rays becomes energy transfer afterwards by absorbing of the material.
Each photon carries its own energy. After absorbing of the molecule, it is a process from a low-energy state to a high-energy state occurs,
with energy changes in different directions. Part of ultraviolet rays becomes light.
Some fluorescent and phosphorescent substances of ultraviolet rays emit some fluorescence and phosphorescence.
The other part of ultraviolet rays may internally dissipate into heat.
There are also changes in molecular structure, photochemical reactions occur, and produces new substances.

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