The light producing substance in Glow worm/fire fly is

The light producing substance in Glow worms/fireflies is Luciferin.
Luciferin is the compound that produces light. In a chemical reaction, luciferin is called the substrate.
The bioluminescent color (yellow in fireflies, greenish in lanternfish) is a result of the arrangement of luciferin molecules. Some bioluminescent organisms produce (synthesize) luciferin on their own.