Chemiluminescence
Chemiluminescence is light produced by a chemical reaction instead of heat, like the glow inside a glow stick.
Think of it this way
Two bottles of chemicals sit on the kitchen counter. When you pour one into the other, the mixed liquid starts to glow. No flame, no heat — just light from the mixing itself. The chemicals swap tiny particles between them, and that swap releases energy as light instead of warmth.
Explaining chemiluminescence by grade level
When you bend a glow stick, it starts to shine. No batteries, no fire, just light from mixing two liquids inside. The snap you feel breaks a tiny glass tube, letting the liquids meet. When they touch, they make light. The stick feels cool because the glow comes from the mixing, not from anything hot.