Eli5 what determines the color of things?

Question

I understand that light of different wavelengths reflected is what gives off color but what determines which wavelengths, a table, for example, will reflect or absorb? Is it something encoded in the table itself or is it the light that communicates the color?

Why do some things absorb all wavelengths turning them black while others reflect all turning them white?

In: 7

Answer 1

Electrical engineer here, I’ve studied the physics of light a decent amount in undergrad.

So a lot of what is happening is the molecular, chemical, and atomic structure of the material.

So you mentioned a table. Picture a table made of wood. The type of wood will have its own color that can range from a light, warm tan/yellow to browns to greys (and more). Wood is mostly a lot of carbon, hydrogen, and oxygen atoms (with perhaps some others sprinkled in such as nitrogen) and harder woods – oak, walnut – will have a slightly different chemical make-up and the packing of the molecules are denser than softer woods – e.g. pine.

Photons are little packets of an oscillating electromagnetic field, and sunlight contains the full spectrum of visible and invisible light. When photons from sunlight hit the naked wood on the table, some of them are absorbed by the electrons in the atoms of the wood. This tends to warm up the table. Other photons get reflected, and some in the non-visible spectrum may pass through entirely!

The photons that get reflected vs absorbed or passed through are filtered based on the frequency of the photon – i.e. the color of the light that will hit your eyes – and the chemical make-up and even the crystalline structure of the molecules. Specifically which color ranges respond to what kinds of chemical compounds or structures is beyond my knowledge, but that is how it is determined.

Then there are things like finishes, dyes, paints, etc, which can change what we see. These compounds have their own chemical makeup and they are specifically engineered and chosen to absorb and reflect certain frequencies of light, which is why you can paint or stain wood, or dye cloth, and change its color.