Each one of them changes in some respect if you look at them with the light humans can’t see. As I’ll later refer to them by number, here is the list:
1. A UV-A lamp.
2. A silver bar in a plastic bag.
3. US one cent copper coin.
4. A ring made with Rhodium.
5. A shot glass with white wine in it.
6. Plastic cutting board, probably made of PVC.
7. Some green grass in the background.
8. A shot glass with red wine in it.
9. A piece of black plastic trash bag.
10. A piece of paper with a stripe of sunscreen applied to it.
11. A diode flashlight.
12. A wooden pencil.
13. An 0.8 mm thick Silicon plate.
14. A burning candle.
15. A heart-shaped piece of foggy quartz or possibly selenite.
Ready to switch vision? Lets go.
Ultraviolet World, 350–400 nm
What changed?
1. The UV lamp is very bright. No surprise: we are filming in UV now.
2. Virtually no change to the silver bar. I was hoping to observe darkening known to exist below ~350 nm, but apparently my filters did not let that through.
3. But copper coin did darken. It is known that copper is a poor reflector of near UV.
5. White wine… isn’t white anymore! It is almost black and non-transparent! This works with grape — but not with peach wine.
6. The cutting board changed color dramatically. And all cuts and scratches became prominent. So, you can use UV photography to distinguish a freshly used board from the one that’s been sitting idle for a while :)
7. The grass is also dark in UV. The effect extends to nearly all foliage and was somewhat of a trouble to early photographers who worked with old orthochromatic black and whit film.
10. Sunscreen stripe stands out very clearly. That’s another practical application of UV photos: finding spots of missing sunscreen before going out into tropical sun.
11. What happened to the diode flashlight? It is not anymore… No, I did not switch it off. It just emits nearly no UV light. Which is good for museums seeking to protect paint art from destructive effects of UV.
12. The pencil is also darker, though that could be attributed to its yellow paint.
14. Candle flame turned nearly invisible. This is expected. It takes quite a high temperature to start shining in UV.
15. Finally, the “heart”. It is opaque now because of the effects of Rayleigh scattering.
Near Infrared World, 750–900 nm
- Now the UV lamp is completely screened by the filter.
2. The silver bar got darker, though we know that silver reflect IR very well. Why? Because it is reflecting mostly the blue light off the sky. And as we cut off that blue together with most of the visible light, the sky turned dark, and so did the reflection.
3. Still, the relative brightness of Rhodium is lesser than that of shiny Silver or Copper. That, actually, is expected (see Figure 5).
5. White wine is transparent now. And so is the red wine (#8), too! Both look just like water.
7. The grass is much brighter than asphalt in IR, which is common to most foliage in that range.
11. No visible IR emission from the diode flashlight.
13. But the candle’s flame is prominent, which is expected since it is a rather low-temperature thermal emission.
15. And the smoky stone heart, what happened to it? It is completely transparent now, just like some ordinary glass.
Near Infrared 1000–1050 nm
The changes mostly continue the trend set by the previous IR picture… but there are some peculiar details.
13. The Silicon plate is completely transparent now — you can see through it.
14. The candle’s flame is even brighter, as we are moving closer to the thermal range.
And no, the white wine did not get darker. This is a vignette effect produced by an imperfect IR filter.
In case you are wondering, here is what the filter looks like. Yes, thin Silicon is transparent to digital cameras near 1000 nm.
Thermal Infrared, 6–14 mkm
The next photos are truly thermal infrared. They “see” the heat, even as modest one as the heat of a human body. As the shots were made from two slightly different vantage points, I’m presenting two views of slightly differing compositions to illustrate all the effects.
The changes are:
5. The shot glasses are opaque, and clearly their content is cold.
9. But you can see through a piece of black plastic now. It is better observed on the lower picture, where the bottom of the shot glass and the pencil clearly stand out though the plastic.
10. Funny enough, the sunscreen is a bit hotter than the paper it is on. That’s probably because it absorbed enough of UV light (compared to paper) to release it back as a heat now.
11. The flashlight makes no heat, as diodes are quite efficient light sources.
13. The Silicon plate is still transparent!
14. The candle is very bright, though because of unlucky camera positioning it’s rather hard to notice (and there is no candle on the lower picture).
Combined
Per great suggestion of my friend Andrey Lelikov, I also combined the UV and two IR photos into a color map.
In this picture, blue was assigned to UV channel, green to near infrared 750–900 nm, and red to IR of 1000–1050 nm. Now the differences clearly stand out!
· Red objects are those transparent or reflecting only in further ranges of IR
· Yellow and green are good near IR but poor near UV reflectors/transmitters.
· Same for green (the edges of the photo are greener due to vignetting from the Si filter)
· Blue are UV bright things.
