Why can't we see our bones (like we can our veins) when a flashlight is held against a hand?

Bones are less definitive, meaning, we could just see their outline. That and veins are closer to the surface, I think it has to do with density, to see bones you have to go through more skin. Why do you want to see bones so bad, I’ll show you a bone.

Right. Bones are dense so you just see the outline. You need much high energy particles to see definition through bone. (i.e. x-rays)

I found a post at The Straight Dope that says dispersion of light is why bones don’t get imaged in this manner. (see link for crude diagram).

Infants, on the other hand, have small enough hands to trans-illuminate with strong light & probably see bones & cartilage.

Your bones are like the bottom of the ocean and your flesh is the water and your veins are dolphins. You can’t see the bottom of the ocean because it’s too deep and if you added enough light to see it you would probably vaporize the dolphins.

@Zyx Ha! I like that answer. :)

@DrasticDreamer Thanks! :D

The reason veins show up when there is a light behind them has to do with the color absorption spectrum of the dexygenated blood. It is the same reason that the probe on your finger can read how much oxygen is in your blood.