The ultra violet light produced by exited mecury atoms ( which in turn produced by collision of electron from cathod) is converted to visible light by phosphor.
Requirement of Ballast
- Electric energy transformed into the energy of fast moving electrons in the tube.
- These electrons excite Mercury in the tube by collisions.
- Excited Mercury emits Ultra Violet (UV) radiation.
- The phosphor coating on the tube wall transforms this UV radiation into visible light, which pass through the glass.