Why does from blue to red light (after crossing a prism) the heating effect on interaction material increase?

Question

I was reading this paper for Near Infrared discovery The history of near infrared spectroscopic analysis:

In his experiment Herschel projected a rainbow on to a bench by the aid of a prism then he measured the relative heating effect of different parts of it (Fig. 1). As he moved from the blue to the red the heating effect increased.

I was confused because I know that red photon carries less energy than the blue one.

1. Is the increased heating effect from blue to red caused by the different photons speed in the prism material ? And so, after prism material, red photons are in greater amount than blue one and the total energy that is carried is greater than the blue photons ?

2. If it is so, how can I know how the material modifies photons velocity ? For example, in the air I imagine that this is not true any more since there are blue light glasses, also known as blue anti-light glasses or computer glasses, which have been created to decrease the amount of blue light.

Answer 1

This is a wonderful question!

Yes, blue photons carry more energy than red photons.

You've guessed one explanation, that maybe they all have the same rest energy, but some are moving faster.

You're right; in fact, the blue photons DO have more energy. But because they don't weigh anything, it doesn't matter how fast they go. In fact, they all go at the same speed.

Photons store energy a different way, in the angular momentum of how fast they rotate. In fact, that's all they are, beautiful little particles of nothing but pure angular momentum.

In fact, the red end of Herschel's rainbow gets hot because there are far more red photons in sunlight.

See, everything broadcasts radiation of all colors, but hotter stuff is bluer.

Our sun is yellow, but hot young stars are blue. Black hole discs are hot in X-rays. Exploding stars emit thermal gamma.

Isn't that cool?

Or hot?

Answer 2

When light passes through a prism, it refracts and spreads into its component colors, with blue light bending more than red. This is due to the difference in the refractive index of the material for each wavelength. Shorter wavelengths (blue) interact more with the medium, causing higher energy absorption and thus potentially increasing heating effects. As light travels through a medium like air, the refractive index changes minimally, so the speed of light remains almost constant. Blue light glasses are designed to filter out the higher-energy blue wavelengths, reducing eye strain rather than affecting the speed of light in the air.