Final answer:
Light is composed of photons, not calories or pigments. These photons are packets of energy with specific wavelengths that correspond to different colors in the visible spectrum, with shorter wavelengths having more energy than longer ones.
Step-by-step explanation:
Light is a form of electromagnetic radiation composed of energy units called photons. Unlike the misconception that light consists of calories or pigments, it is essentially a stream of photons, with each photon having a characteristic wavelength that determines its color in the visible spectrum.
When discussing light energy, it is essential to understand that this energy is part of a much broader electromagnetic spectrum emitted by the sun, which includes various types of radiation. In the context of visible light, energy is quantified by measuring the wavelength of these photons, with the visible spectrum ranging from about 380 nm (violet) to 720 nm (red). Shorter wavelengths correspond to higher energy photons, and longer wavelengths correspond to lower energy photons.
A typical source of light, like a light bulb, emits an astonishing number of photons every second. Such photons, each with their specific energy based on their wavelength, illuminate our world. This explanation disproves the options 'calories' and 'pigments', confirming that the correct answer to the question of what units constitute light is photons.