www.pilotballoon.com "the pilot balloon web resource" 

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Pilot Balloon Water Activated Lighting Unit

The water activated lighting unit dunked in a bucket of water and then tied to a balloon for night time observations.  It uses a water activated battery.   They are shipped in lots of 10 in the can pictured.  The lighting units are packed in desiccant to preserve the battery power. 

VIZ http://www.sippican.com/meteorological.html manufactured the Pibal lighting unit pictured below as well as a line of radiosonde units, some that are in current use.  VIZ was purchased by Sippican Inc.  They are now located at 7 Barnabas Road, Marion MA 02738.  As far as I can tell from their site, they only make modern Radiosonds, and not lighting units. 

Check Novalynx for availability and pricing of Pibal Lighting Units

vizlite.jpg (39325 bytes) Photo of a Type S Pibal Lighting Unit

VIZ Manufacturing, 335 E. Price Street Philadelphia PA 19144 is the address on the container.