How do incandescent light bulbs work?

It depends on the type of light. Both Fluorescent lights and LEDs initially emit light in the UV range or near-UV range (high energy). This light is then absorbed by compounds which re-emit the light at longer wavelengths (lower energy). The difference in energy between what the compound absorbs and what it emits is dissipated as heat.

Different compounds emit different wavelengths when excited by UV light. By using a cocktail of compounds, a wide variety of wavelengths can be emitted, producing a spectrum that is very similar to that of natural light.

Full spectrum LEDs use a different compounds than fluorescent lights do, but the concept is the same.

Full spectrum lights are different from many so called white lights in that white lights usually emit only three or four discrete wavelengths. The eye averages the different wavelengths together to give the perception of color. If the ratiOS between the intensities of the wavelengths is just right, the light appears white.