Science
What is Fluorescence?
Fluorescence is when a material absorbs light at one color and quickly re-emits it at another, usually glowing under ultraviolet light. The material soaks up high-energy light and releases it as visible light — the effect behind highlighter pens and blacklight posters.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains fluorescence.
Key things to understand
- 1A substance absorbs light (often invisible UV) and re-emits visible light.
- 2The emitted light is lower energy, a different color than absorbed.
- 3It stops the instant the light source is removed.
- 4It's behind highlighters, blacklight effects, and some minerals' glow.
- 5Phosphorescence is similar but keeps glowing after the light stops.
Frequently asked questions
- What causes fluorescence?
- A material absorbs high-energy light, its electrons jump up, then drop back down releasing the energy as visible light of a different color.
- What's the difference between fluorescence and phosphorescence?
- Fluorescence stops instantly when the light is removed; phosphorescence stores the energy and keeps glowing for seconds to hours.
- Why do highlighters glow under blacklight?
- Their dyes are fluorescent — they absorb the UV in blacklight and re-emit it as bright visible light.