If a wave is the same frequency of light, but does not contain photons, it is not light, correct?

Question

And if so, then why is light and the color spectrum often included in charts of the RF spectrum?

To clarify: can a wave exist at the frequency of light, but not consist of photons, and thus not e light? And we wouldn't see it then... so we could use it for communications, or whatever else?

Answer 1

Waves occur in many things, but photons are only associated with electro-magnetic waves. A photon is the smallest carrier of energy in an EM wave, the so-called quantum of energy equal to Planck’s Constant multiplied by the frequency of the wave. Photons exist not only in visible light, but in all EM waves.

Regarding frequency conversion of EM waves: the most common is Doppler shifting, which occurs as an increase in frequency when a radiation source is moving toward an observer, or a decrease in frequency when the source is moving away from the observer. Other methods include interaction with non-linear materials either alone or with a mixing wave, the latter producing heterodyne waves whose frequencies are the sum and difference of the two waves.

If you could move away from a gamma ray emitter fast enough, its wavelength as observed by you would be down-shifted into a visible wavelength. If you could move toward an infrared emitter fast enough, its wavelength as observed by you would be up-shifted into a visible wavelength. Smaller wavelength shifts are observed in the spectra of stars and are used to determine the relative motion of the star toward or away from the observer.

Regarding other waves, such as vibrations in matter like sound, there is no fundamental reason that I know of why such waves could not exist at the same frequency as visible light. But being mechanical waves, we would not perceive them at such high frequencies unless their energy was converted to something our senses are sensitive to, like heat.

Maybe someone with imagination could use them for communication.

See this web site for further understanding:

http://www.physicsclassroom.com/Class/light/u12l2a.html

Answer 2

Because Light exists in two forms simultaneously. Particle and wave. Light and RF are separate component parts of the electromagnetic spectrum. Light is shown on a chart of the RF range to show the boundary. You see, you're assuming that RF is a spectrum of its own when it's merely a section of one.

Answer 3

well 3 years back when i was at school (right now i'm doing my computer engineering) when we were taught waves i had asked a similar question to my physics teacher- i had asked this "suppose we somehow (hypothetically) find out a way to reduce the frequency of gamma waves such that we are able to reduce their frequency to that of the red light part of visible light spectrum, then will those gamma waves with reduced frequency be identical to the real-world red light in all respects". to put it more clearly, is frequency the only difference between various parts of the electromagnetic spectrum- meaning thereby that if its somehow possible to change frequency, then we can convert gamma waves to ultraviolet, or infrared to gamma and so on. i did not get a satisfactory answer to my question, and till date i haven't got answer to this question anywhere. i am sharing this with you because your question looked very similar to me, and also brought back school memories to me. my personal opinion based upon whatever i have studied till now is that EM waves really differ only in frequency and not in their 'fundamental nature' or constituents (whatever they are). its just us humans who have classified the entire EM waves spectrum into visible or non-visible based on what 'we' can see or not-see. in absolute terms there is no visible or non-visible EM waves. the classification makes their study better, whereas in absolute sense, they all should be of similar nature

finally, i got another insight on your question. you asked that "if a wave" and not "if a electromagnetic wave". which means that your question applies to matter waves too, and to all non-electromagnetic type of waves. so suppose a matter wave exists [or maybe a sound wave exists] with frequency equal to red light, then it certainly is not light. your question stands solved in my opinion.