Or alternatively, are we breathing in light particles into our lungs all the time?
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Light has energy, but not calories specifically, as calories are energy in food or drinks. Bodies like plants can absorb the energy from light, but are not good at converting that energy into the chemical energy we use for movement etc.
Calories are just units of energy, so you could technically calculate the number of calories in a photon. Green light has a wavelength of 550 nm, and the equation for photon energy is hc/L, where h and c are constants and L is the wavelength. [It works out to be about 10^(-19) calories](https://www.wolframalpha.com/input?i=hc%2F550+nm+to+calories) in a photon of green light.
Of course, you can’t *eat* light. Digestion extracts energy by breaking apart chemical bonds; our cells use sugar to get energy in the form of a molecule called ATP. Light has energy, but it isn’t usable by your cells. Similarly, we aren’t really “breathing in” light. Breathing moves air in and out of our lungs. Light isn’t a gas so it doesn’t move in and out of our lungs like that. Light is a completely different category of particle from anything tangible that you might interact with like food or air
Light does have energy, but your body can’t really do much with it directly. However, you eat the energy from light all the time. All of the food we eat can be traced back to sunlight. Plants DO have the ability to use sunlight directly to grow. We eat those plants and we also eat animals that are those plants and used that energy to grow.
So basically we all live by eating the sun.
Light isn’t a particle like a dust particle. In physics a particle means a unit that has consistent properties.
Imagine you have a long rope. You wave one end of it and a wave starts to travel down the rope. You can view that wave as a unit. A light particle is similar to a wave on a rope. But it has other weird properties so it’s not like a wave on a rope with minor changes in behavior.
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