What is the white powder in fluorescent bulbs?

The white powder in fluorescent bulbs is phosphor. Phosphor transforms invisible light waves into light that can be seen by the human eye.

Phosphor, short for phosphorus or the chemical symbol "P," is an element that has the atomic number 15. Phosphorus is found in the human body and in nature. In its purest form, the element is colorless and can catch fire in the air. It also heats when exposed to artificial light or to sunlight. Phosphorus was first discovered in 1669 by the German scientist Hennig Brand. After it was discovered, it was obtained by extracting it from urine.