I purchased an infrared light. It's a 100 W Philips infrared lightbulb. Says it's infrared, but I haven't done any spectrum analysis so I don't know for sure if it's just red or really infrared.

As I recall glass is specially opaque to infrared light. Doesn't the light bulb have to be of special glass? (I may be wrong in my assumption, though.)

Assuming a non absorbing material, I always think of longer wavelengths as having higher lattice penetration power as longer wavelengths collide with less particles as they travel. Although humans are not very lattice-like, I just want to know if what it says on the box is true or not. That it has more penetration power than a pure white light bulb, and it's really not just warm because of Joule effect (100 W is a lot, after all). Mostly, I think of low energy radiation as harmless to humans.Is infrared radiation so?

  • 2
    $\begingroup$ I have voted for reopening. 1) the questions have an answer in physics. 2) I thought we had discussed in meta not to jump on new users full force. // maybe the third subquestion belongs to biology and could be omitted. $\endgroup$
    – anna v
    Jan 22, 2013 at 14:10
  • $\begingroup$ @annav: I've reopened it for now. The main issue is that it's too many questions rolled into one. Usually I'd leave a comment asking the user to split it and I'll reopen, but looks like the comment got eaten by my Net connection this time :s Remember that closing with a comment is not "jumping on new users". Closing isn't permanent, a post gets reopened if improved. $\endgroup$ Jan 23, 2013 at 5:13
  • $\begingroup$ Fullmoon, you may want to remove the last part of your question. It is off topic and slightly asking for opinions. Aside from that, there are too many questions in this question. So it's best if you remove the bonus question from your post entirely. $\endgroup$ Jan 23, 2013 at 5:15
  • 2
    $\begingroup$ You may be thinking of how glass is very opaque to UV (and so UV-transparent optics are made of expensive quartz). Normal glass may not be perfectly IR-tranparent, but surely you've felt warm on the side of your body facing the Sun, even when inside a car? $\endgroup$
    – user10851
    Jan 23, 2013 at 6:25
  • $\begingroup$ @Manishearth thanks. you are correct about the too many questions, but he/she is a new user and the standard closing comment must be very intimidating. there is nothing argumentative or such in this question. maybe a new reason for closing until some change is made, that is special for new users should exist. $\endgroup$
    – anna v
    Jan 23, 2013 at 7:34

1 Answer 1


In table 1 the classification of photon frequencies is given.

A lamp as you describe will emit most of the energy in the infrared and some in the visible. The energy carried by the visible part will also end up in the infrared degraded by the reflections in the room. So you will get 100watts in total.

The advantage of emitting mostly infrared lies in that people and walls do not reflect it but transform it into molecular motion directly, i.e. heat. One has a "heat beam" for drying, instead of a convective drier. Larger infrared emitters are used as room heaters, heating walls and furniture and people directly instead of waiting for air convection to do the job.Infrared is safe. It is the range in which biological organisms thrive.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.