DIYbanter - View Single Post - UK question: ES light bulb better than bayonet?

wrote:

In the UK screw caps are mainly used on discharge lamps, such as SON
(high pressure sodium), metal halide, mercury etc. For some reason SOX
(low pressure sodium) lamps use bayonet caps. I prefer screw caps;
they hold the lamp more securely, important with large or heavy lamps,
such as the early Philips SL ones, and contary to the experience of
others here, I find that they're less likely to stick in the holders.

Good point! They are relatively heavy, expensive bulbs, mounted on
poles where there may be movement and vibration. So the mounting
system must be secure. The fixture may get wet on foggy days, so
the system can't be prone to corrosion and sticking. The
maintenance man may be on a metal ladder against a metal pole, so
the system must be safe.

The designers of these bulbs must have found that Edison bases could
work very well. (One problem in America is that two of the most
popular sizes of sodium bulbs use the same size base. It may not be
apparent which size a fixture requires. If the bulb doesn't match
the ballast, it will keep cycling on and off, and nobody may know why.)

A maintenance man probably wouldn't use pliers to unscrew a base
unless he knew for sure the circuit was dead. Skin resistance is
usually pretty good protection against serious injury from household
voltage, but it won't protect you so well if you're gripping metal
pliers. On the few occasions I've unscrewed the bases of broken
bulbs, I've used rags, not pliers, which could cause an arc besides
a shock. A rag distributes the force you apply and reduces the
possibility of glass getting in the eyes.

I'm more mistrustful of bayonet bases than Edison bases. Most
bayonet bulbs I deal with are automobile tail lights, which may have
been corroding and vibrating for decades.

An American can save money by buying unfamiliar foreign brands of
Edison-base bulbs. They may be more troublesome than the familiar
brands. I can buy an American brand with confidence because the big
American companies have lots of experience making Edison-base bulbs
and they are competing for customer loyalty. That's probably true
of bayonet bulbs in England.