# Light - electromagnetic frequency

## Main Question or Discussion Point

hi Guys,

if i have 2 sources of "light" that both have an electromagnetic frequency of 200 THz (infrared/invisible).

- now, if i shine both of them into my eye at the same time, will i see light at a frequency of 400 THz?

greetings...

( ps: i'm not going to try this and i suspect that it is dangerous and not possible, just mainly wanna know why )

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Redbelly98
Staff Emeritus
Homework Helper
Welcome to Physics Forums.

If you combine two "lights" that have the same frequency, the result will have the same frequency as well. So, in your example, still at 200 THz.

To get double the frequency, you would need a special nonlinear material to convert the 200 THz into 400 THz. This can be done, but again it requires a special material, it does not just happen as a matter of course.

Staff Emeritus
2019 Award
No. The reason is "why should it?" If it's 70 degrees in Los Angeles and 50 degrees in San Francisco, it's not 120 degrees in California. There's no reason to add temperatures and there is no reason to add frequencies.

Rap
For visible radiation, the frequency is the color of the radiation. If you shine two red lights into your eye, you won't see blue, you just see red at double the intensity. When you add two beams together, you get double the intensity, not double the frequency. Well, thats not completely true, if its like a laser beam, then you can have phase cancelling, but if the beam has a mix of frequencies in a large enough range around the center frequency, then it will pretty much add up intensities.

Redbelly98 - didn't know that there were materials that could do that, that's just the kind of information i was looking for... thanks

Vanadium 50 - i understand what you mean but i guess you kind of missed the point of my question

Rap - i will think about that thanks

sorry for the late reply, i was distracted.