Why Does Black Light Illuminate White Objects?

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Discussion Overview

The discussion revolves around the phenomenon of black light and its interaction with white objects, specifically exploring why black light appears to illuminate only white items. The scope includes conceptual understanding and technical explanations related to light and fluorescence.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why black light illuminates only white objects, suggesting a need for clarification on the underlying principles.
  • Another participant draws a parallel between black light and red light, proposing that the mechanisms of illumination may be similar.
  • A later reply challenges the initial analogy, stating that if the analogy were correct, objects would only emit UV light, indicating a misunderstanding of the process involved.
  • Further elaboration is provided on how UV light is invisible and that fluorescent lamps convert this energy into visible light through phosphors, which fluoresce when exposed to light.
  • Participants discuss the process of energy absorption and emission in phosphors, noting that the emitted light has less energy than the absorbed light due to energy loss as heat.

Areas of Agreement / Disagreement

Participants express differing views on the analogy between black light and red light, with some agreeing on the need for clarification while others contest the validity of the comparison. The discussion remains unresolved regarding the precise mechanisms at play.

Contextual Notes

There are limitations in the discussion regarding assumptions about the nature of light absorption and emission, as well as the specific roles of different wavelengths in the fluorescence process. Some mathematical steps and definitions related to energy levels and photon interactions are not fully explored.

daniel_i_l
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Why does black light (florecent light without the coating) light up only white things?
 
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I believe what you are asking is the same type of question as:
"Why does red light only light up red and white things?"
I think it's the same answer too ;)

Whatever howstuffworks says is probably more correct and thorough
 
moose said:
I believe what you are asking is the same type of question as:
"Why does red light only light up red and white things?"
I think it's the same answer too ;)
Um, if that were true, the object would only emit UV. In fact, it is emitting a different wavelength than that which it is absorbing.
 
DaveC426913 said:
Um, if that were true, the object would only emit UV. In fact, it is emitting a different wavelength than that which it is absorbing.
Yes, but read this
howstuffworks said:
UV light waves are too short for us to see -- they are completely invisible -- so fluorescent lamps have to convert this energy into visible light. They do this with a phosphor coating around the outside of the tube.

Phosphors are substances that give off light -- or fluoresce -- when they are exposed to light. When a photon hits a phosphor atom, one of the phosphor's electrons jumps to a higher energy level, causing the atom to vibrate and create heat. When the electron falls back to its normal level, it releases energy in the form of another photon. This photon has less energy than the original photon, because some energy was lost as heat. In a fluorescent lamp, the emitted light is in the visible spectrum
 

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