found a great list of explanations of let handed threaded light bulbs at this site, along with the specific snipit
http://www.globalspec.com/Newsletter/ViewIssue?vol=Vol3Issue20&pub=1&isPastIssue=1The Challenge - Left-hand Threaded Light Bulbs...
The situation presented in the last edition of the newsletter was: What were light bulbs with left-hand threads made for, and why were they made this way?
Answer: Light bulbs with left-handed threads were originally made for use in public places, such as on trains and subways. The intent was to curtail theft ? as they were useless in the home, no one would steal more than a few before realizing the bulbs wouldn't work with a regular base. These bulbs can still be purchased; they fall under the classification of specialty bulbs.
Here's a sample of your responses...
"Light bulbs with left-hand threads were used on New York City subway cars. There were made this way because they had a problem of the light bulbs getting stolen by the passengers. The passengers were stealing them to use them at home. Changing to left-hand threads made the light bulbs worthless to steal because nobody had left-hand threaded bulb sockets at home."
"Light bulbs with left-hand threads were made for use in public places to deter thieves, because they would not fit in residential lighting fixtures."
"Left-hand bulbs are often used in temporary lighting strings at construction sites. Left-hand threaded bulbs do not fit in normal Edison-based sockets found in most incandescent fixtures, so therefore no one would want to steal them."
"The reason left-hand thread bulbs are made is quite simple: people won't steal what they can't use."
"Left-hand threaded bulbs are produced for use in public places. This is to deter theft, since one cannot use them in standard household fixtures. Left-hand bulbs are still available... make the perfect gift!"
"The reason for light bulbs with L-hand threads is a safety concern. On rotating equipment that is spinning in a clockwise direction, L-hand threads are necessary so that centrifugal force is directed in the tightening direction rather than loosening, thus preventing the bulb from becoming a flying projectile and a bonanza for personal injury lawyers."
"You can still buy left-handed light bulbs for the purpose of theft prevention (New York’s subway system is one such client), but I seem to remember something about Tesla’s fight with Edison over DC vs. AC current having something to do with the evolution of right vs. left-hand bulb threads. (This is only a vague, semi-recollected memory of something from long ago, and has no scientific validity.)"
"Construction sites so people would not steal them. I think this goes along with the little boy on Art Linkletter who, when asked what his father did for a living, said, "My father makes light bulbs and toilet paper." When asked how he knew this, the boy responded, 'That's all he brings home from work.'"