This works, submerge the lamps in hot water and strong bleach solution, half a day should do it, this will remove yellowness from the glass, inside and out, and also return the adhesive sealer back to white again. When done, rinse with very hot tap water, and allow to drain, final drying can be done with a hair dryer/hot air gun... your lamps will be sparkly like new again

Remember to use gloves and goggles if using bleach, and out of anyones way. Safety first

Thom