Mercury Vapor Lamp: Why 20-30 Minute Delay?

[gkiverm]

I've been reading up on mercury vapor lamps, which are often used as a light source in fluorescence microscopes. I still don't understand why it decreases the lamp's lifetime if you turn it on and switch it off without waiting 20 - 30 minutes. Is there a reason for this?

 

[Andy Resnick]

This is called a 'hot restrike', and much higher voltages are required than the usual 'cold start'. For our arc lamps, we simply can't perform a hot restrike- the starter doesn't put out enough voltage. I'm not sure if a hot restrike decreases the lamp lifetime over and above normal operating cycles.

 

[Drakkith]

Do you need to wait 20-30 minutes for the lamp to heat up after you turn it on, or for it to cool down after you turn it off?