i want to know the source of light emitting from the green paint of some watches at the night.?

Answer 1

Most modern wathces use a combination of ZnS (zinc sulfide) and the radioactive material Thorium (Th). Some watches also use Rhodium (Rh) but this is more rare. Almost no watch contains Radium (Ra) anymore. The radio-active elements radiate energy which makes thedials glow in the dark. Hope this was helpful for you.

Answer 2

Atleast in the earlier watches, they used to have combination of some radioactive salt and a flourescent paint. In fact they were called radium dials and we used them in sixties to demonstrate the radioactivity by bringing them near a GM counter and showing the activity in the counter. I am not sure what they are doing now, esp. since manual painting of the dials was banned because of the intake of the radioactive salt by the painters who were licking the brush to keep the brsitles closely grouped.