I never had a mercury vapor bulb breaking on me in the last thirty years, but I always had a little, pathetic rain cover on top of it and stopped when it was starting to rain substantially. I heard that rain might break the glass, be it ballasted or not, but the few drops that my bulbs experienced did not cause any damage. My bulbs were made in Japan, Czech Republic, and Germany, but I think I had the odd Chinese one, too. GE is US and as such trusts in communist manufacturing and lower quality, I guess.
I think all glass bulbs are prone to break when they are hot and suddenly exposed to substantial rain. Try to install a cover above it. If it rains sideways, then just have a beer inside.

Dr. Frank-T. Krell
Curator of Entomology 
Commissioner, International Commission on Zoological Nomenclature
Chair, ICZN ZooBank Committee
Department of Zoology 
Denver Museum of Nature & Science 
2001 Colorado Boulevard 
Denver, CO 80205-5798 USA 
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Phone: (+1) (303) 370-8244 
Fax: (+1) (303) 331-6492
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-----Original Message-----
From: Scarab Beetle Taxonomy Discussion List [mailto:[log in to unmask]] On Behalf Of Anuar Morales-Rodriguez
Sent: Wednesday, June 10, 2015 11:54 AM
To: [log in to unmask]
Subject: Re: Bulbs for light collecting


I had very similar problem in Montana, bulbs broke very often but not in Colombia. The different was the brand, here they were Philips and in Colombia GE.  No sure if they were made in China or  not.

-----Original Message-----
From: Scarab Beetle Taxonomy Discussion List [mailto:[log in to unmask]] On Behalf Of Auke Hielkema
Sent: Wednesday, June 10, 2015 9:20 AM
To: [log in to unmask]
Subject: Bulbs for light collecting

Dear all,

For light collecting, I use mercury-vapour bulbs (125W and 250W) with external ballast. My 250W is still good after probably over 100 nights of collecting, but the 125W broke about a year ago. I bought a new one, which lasted about 10 nights before the glass broke while collecting on a rainy night. The next also lasted only for some nights before the glass broke. They still worked, but because of the intense UV-radiation they give off when unprotected by glass I turned them off. I now bought yet another one, but noticed that the packaging says it should be protected against contact with cold objects and water while burning. However, I thought bulbs with internal ballast should be kept dry, while those with external ballast can be used in the rain without trouble. Could it be that these bulbs have become lesser quality? The bulb is a Philips HPL-N, but produced in China. I'm not sure where my first bulbs were made.
The lighting shop I buy my bulbs from may be able to get me other brands, but what brand should I order to enable me to work in the rain?

Thanks in advance for your advice,