I recently bought an IKEA spotlight. (JANSJÖ Clamp spotlight, product number 80163192) For fun I tried cupping my hand around it in a dark room to make the light shine through my hand. I could see my own veins. Pretty cool. I used to this with flashlights as a kid, as well.
Of course, I felt the need to document it. But these pictures look considerably different from what I could see with my naked eye…
The photo has a pink tint and the sensor is saturated in the area between my fingers. (There was no open gap between the fingers.) What the how, you might ask? Let me tell you, the camera is picking up infrared light. The human doesn’t react to IR light, but digital cameras generally do react to near-red IR to some degree. There’s typically an IR high pass filter to remove the mostly unwanted IR, but it’s not perfect. Handy tip: You can also use this effect to test whether a remote control or Wii sensor bar is working by pointing it toward the camera, pressing a button/turning it on and looking at the screen.
So the LED is apparently emitting quite a lot of IR, and my flesh is apparently pretty transparent to it. What about some fruits? For this experiment, I made hole in various fruits and mounted to the lamp head, making sure no light escaped out the back. I put a plastic bag over the lamp head so it wouldn’t get dirty, of course.
The effect on the apple is certainly not as pronounced as on my hand, but you can see it in the shadow, as well as some fringing around the edge of the fruit.
The last fruit to get this treatment was a kiwi. As one might expect, the thick skin and colored pulp made this shot less interesting from an IR point of view, but they are still included below. The difference in color is from experimenting with different ISO values. The last picture shows where the lamp head is shoved into the fruit with the “condom” on.
And lastly a semi-unrelated photo: This is some form of residue in my sink that I couldn’t remove easily. I think it’s a drop of grapefruit juice that has dried out. It’s the Death Star!