You need a UV lamp to harden it - but don't leave the glue container where it can be affected by the lamp as it will harden all of the glue. Shops and dealerships that supply stained glass supplies will have this glue.
There is also a glass glue that is activated by sunlight alone. I have used it to repair glass ornaments. You put the glue in indoors out of direct sunlight, then take it out doors and expose it to sunlight and it sets almost immediately. It works even on cloudy days and I think its a loctite product