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 Definition The part of the electromagnetic spectrum visible to a species' biological eye. [d] [e]
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 Workgroup category Physics [Editors asked to check categories]
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Moving Quantum section

...into the greater narrative to make the entry less WP-like.--Robert W King 10:32, 7 June 2007 (CDT)

Reinstated QM - as light IS QM in effect and description. - you may consider this an editor decision. Robert Tito |  Talk 

Photoelectric effect

The basic idea is that individual photons carry a fixed amount of energy. It increases with frequency (which is why X-rays and UV light can be dangerous), but is otherwise fixed. Now, if you shine a bright light on an electric plate many, many photons will collide with the plate, potentially displacing electrons when they do. There is a certain amount of energy needed to displace an electron from an atom, creating current (or a "click" from a detector). As you start to reduce the light level, the number of photons is reduced, but not the energy. This means that individual photons are still able to displace electrons, but there are fewer of them, and so fewer clicks.

Incidentally, Albert Einstein received the Nobel Prize for his work on the photoelectric effect. Greg Woodhouse 14:49, 7 June 2007 (CDT)

Article needs work

More generally, there are a number of inaccurate or misleading statements in this article. I'm afraid I'm in a bit of a rush and can't really point them out just now, but I'd start with the introduction: light is not the same thing as the transition between energy levels that can cause atoms to emit photons. Greg Woodhouse 15:07, 7 June 2007 (CDT)

I fixed the wording; I hope the intro is more accurate now. The article was only created yesterday.--Robert W King 15:19, 7 June 2007 (CDT)

I understand that, and I didn't mean to be rude. As it happens I had to run (two, no three meetings) and I was trying to say what I wanted to say too quickly. Greg Woodhouse 17:46, 7 June 2007 (CDT)

Defining light

The definition really needs to be changed because it describes one (and by no means the only) mechanism for generating light. Light is electromagnetic radiation falling in a rather narrow frequency band. I'm going by memory here (so look it up), but I believe it's between about 3 x 10^14 and 6 x 10^14 Hz. NASA has a number of educational articles that provide more background.

The important thing here is energy. Anytime you generate photons that fall in the range of about 1.2 to about 8 electron volts (eV) you are generating visible light, regardless of the mechanism. Again, you should look those numbers up (I don't have a table in front of me). Greg Woodhouse 13:24, 8 June 2007 (CDT)

hold it: light also IS invisible light, from hard röntgen to IR wavelengths. Robert Tito |  Talk  13:30, 8 June 2007 (CDT)
I'm getting there, eventually. I realize the article is far from complete. --Robert W King 13:53, 8 June 2007 (CDT)
Well, people do sometime refer to "ultraviolet light" and maybe even infrared (but I hear that less often). I've tended to prefer a narrower range and to speak of ultraviolet radiation (and similarly for infrared), but I'm not an expert. I wonder if there isn't some variation across disciplines here? Greg Woodhouse 14:13, 8 June 2007 (CDT)
I propose that if we're going to delve more specifically into other types of light/energy/radiation that fall in other areas of the electromagnetic spectrum, it should probably fall in an article about the EM. Any seconds, comments?--Robert W King 14:15, 8 June 2007 (CDT)


According to, I am assuming that plasmonic waves are the effect of the energy produced by the displacement or excitement of electrons on a conductive surface.

Is my understanding correct?--Robert W King 10:30, 20 June 2007 (CDT)

I the news release, and I'm not at all sure you are accurately representing the science here (not that I'm an expert). It's best to tread a bit carefully and not make sweeping generalizatons about new areas of research. I'm also not sure that this reall belongs in an article about Light qua light. Greg Woodhouse 11:38, 20 June 2007 (CDT)
I don't want to introduce incorrect information--but if it's an exhibitable, demonstratable property (in terms of the particle behaviors). I think it should be worthy of inclusion; which is why I wanted to bring it up in the talk first. I agree though that theory shouldn't necessarily be included.--Robert W King 11:53, 20 June 2007 (CDT)

Particles and waves

I'm not sure what you have in mind when you say that until recently it was believed that light could only be observed as a particle or a wave. It sounds as if what you have in mind is what is sometimes called quantum collapse: observation places a system in an eigenstate for the operator corresponding to the observable (say spin). My understanding (I haven't looked this up) is that we can indirectly observe superpositions of states. But in any case there is no dichotomy here, therfe is a whole continuum of supperposed states.

In any case, though, this isn't an article about quantum theory. Certainly, quantum mechanical properties of light need to be discussed, but in its (their?) proper perspective. There's a lot to discuss here: (visible) light as a portion of the electromagnetic spectrum, optical properties of light (lenses and mirrors and such), light as energy, fiber optics, vision, light as an energy source, black holes, the effect of light on people, photosynthesis. etc. Greg Woodhouse 11:50, 20 June 2007 (CDT)

I agree that there's a lot missing. A recommended outline would be fanastic.--Robert W King 11:54, 20 June 2007 (CDT)


  • definition
  • as energy
    • energy sources
      • effects of light
        • people
        • photosynthesis
  • electromagnetic spectrum (although should have it's own article)
    • visible light
  • optics
    • fiber optics
    • optical properties


I think we should remember that this article is about visible light, not the electromagnetic spectrum. It seems to me that extensive discussion of the wave/particle duality should be moved to the EM radiation article since all electromagnetic radiation is quantum-mechanical. I would focus this article on properties of light that are distinctive to visible light, such as optics, photosynthesis and the difference between additive and subtractive color schemes (e.g. RGB vs. CMYK). General electromagnetic properties of EM radiation should be mentioned of course, but should not be the focus of this article. Warren Schudy 21:59, 20 July 2008 (CDT)