Infrared

[nuttaphong191]

can infrared lights(signal?) go through solids or liquids?

 

[Sceadwian]

Yes. Thin solids, and most liquids. Then again ambient light will too. IR can be best imagined as a colour we are unable to detect. Most silicone optical sensors have frequency responces just outside of human vision, some under the right circumstances can have frequency responcse well outside of it, filters can concetrate this. Look up optical IR photography with common cmos sensors, ALL of them, even those with IR blocking sheets will still detect light above human perception. If you have a digital camera you can see this in your preview pane by shoting an IR remote at it.

 

[mcs51mc]

I'd rather say no

Try your remote with cardboard, paper, glas of water, ... ... between the remote and your TV set. Will it work?


@Sceadwian
I prefer "IR thermography" than "IR photography" because IR radiation comes from heat. You picture the heat sources with a IR camera, not the visible things, it has nothing to do with photons.
That's why you can use a IR camera in the dark. Heat radiation is always there, day or night.

 

[freeskier89]

"Try your remote with cardboard, paper, glas of water, ... ... between the remote and your TV set. Will it work?" Most likely it will work, IR receivers in TVs are extremely sensitive. And the slightest bit of light that is reflected off of the sheets of paper and such will cause the tv to pick up the signal. If you were able to full enclose it with those materials you might see different results.

Considering he said IR "lights", I assume he is referring to near-IR. Thermal IR behaves quite a lot differently than near-IR, because the wavelength is much longer.

"You picture the heat sources with a IR camera, not the visible things, it has nothing to do with photons." Excuse me? It has all to do with photons.

 

[mcs51mc]

The original question was "goes it through solids or liquids".
The answer remains no !
You're absolutely wright, I had a bad example, it can work because of reflection not because the IR radiation goes through the objects.

... ..."IR "lights", I assume he is referring to near-IR. Thermal IR behaves quite a lot differently than near-IR, because the wavelength is much longer.

Now it becomes complicated and theoretical.
All electromagnetic waves of any wavelength (from gamma radiation over visible light to µwaves) are called "light".
So define IR lights, Thermal IR?
All IR radiation from 0.78µ to 1000µ behave in identical way, it's the surrounding objects, atmosphere, windows, mirrors, ... ... that interact (absorption, reflection) with the IR radiation so that it looks like they behaves differently.

 

[ericgibbs]

Glass is actually defined as a liquid.

IR will pass thru translucent glass and plastics.

Special coatings can be applied to the surface of glass/plastics to increase
their reflectivity to IR.

Slightly off topic, but a useful site for the IR-phob.

**broken link removed**

 

[Sceadwian]

Ever notice the dark plastic covering some remote controls? It's opaque to visable light but translucent to IR light. There is also the "Night shot" mode of certain digital cameras that some pervs used to take pictures of women wearing thin IR translucent clothing as the shape of the body underneath could be seen. So of course IR can go through solids or liquids. As I said it's best to imagine it as an extra colour of light that we can't see. That's basically all it is. If you ever get bored and have an old digital camera you want to take apart you can remove the 'hot plate' which is an IR blocking plate they put in and replace it with an ambient light filter that lets IR pass. Do a google image search for IR photography, the images are kind of erie, especially the sky as different cloud layers can be seen and plant life as plants are very IR reflective.