Would infrared or laser be of any help? In a lab setting.

  • $\begingroup$ Would seeing your breath on a cold day satisfy the requirement? $\endgroup$ – mmesser314 Mar 18 at 2:53
  • $\begingroup$ Do you mean measure the amount of water vapour in air? If so you could use its absorption at infrared wavelengths. IR light emitting diodes are cheap and they are available at wavelengths where water vapour has an absorption peak e.g 950nm. $\endgroup$ – John Rennie Mar 18 at 10:07
  • $\begingroup$ Yes @JohnRennie, that's what I was thinking. Do you have a reference to the absorption peak of water vapour? I was wondering if I could use some IR LEDs, and then a filter with a digital camera to visualize the relatively concentration of water vapour. This is used on human subjects during exhalation in PPE masks. $\endgroup$ – Paul Wareham Mar 18 at 19:47

This graph from the Wikipedia article on Electromagnetic absorption by water shows the absorption of infrared light as a function of wavelength - the green line is the water vapour:

Electromagnetic absorption by water

The absorption is greatest in the far infrared, though I suspect equipment that works in this region of the spectrum might be expensive. There is an absorption peak at 950nm, and a quick Google suggests LEDs with a wavelength of 950nm are widely available so it's possible you'd get a useful measurement at this wavelength.

  • $\begingroup$ Thanks. I would also need some kind of camera with a 950nm filter I suppose? $\endgroup$ – Paul Wareham Mar 19 at 22:50

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