On Fri, 21 Mar 2014 08:53:14 +0000, Nightjar
wrote:

====snip====

However, while early lamps were made to exactly match the supply
voltages, a necessity with the poor quality of early filaments,
latterly, if you looked closely at the markings on the lamps, one that
was sold for 220V could be exactly the same as one sold for 240V. People
were so used to buying lamps to match their supply that it was simpler
to put the same lamp in different packages than to try to educate them
to the fact that you could run a 240V rated lamp on 220V, but not
necessarily the reverse.


I'm afraid to say this, but that last paragraph is basically a load
of bull****. Regardless of 'poor quality of early filaments' the
design criteria is still affected by the same physical laws that
determine the life versus luminous efficacy trade offs made with
today's high quality filaments.

The improved quality of filament just allows for an improved luminous
efficacy for a given lamp life (1000 hours being the standard lamp
life arrived at all those years ago as offering the best TCO between
the electricity and lamp replacement costs).

Once you've decided what the lamp life should be, the voltage is
pretty well determined within 1 or 2 percent for a given wattage and
lamp life.

Tungsten filament GLS lamps are very sensitive to voltage variations
that can readily be dismissed by most other domestic appliances.

For voltage variations within +/-25% of nominal, each 5% increase
will approximate to a halving of lamp life (and associated improvement
of efficacy). Conversely, a 5% reduction will double the lamp life and
reduce efficacy.

220v is just slightly shy of a 5% reduction on 'our harmonised 230v
mains' and similarly, 240v is just shy of a 5% increase. It should be
blindingly obvious why tungsten filament GLS lamps have _always_ been
marked with a singular votage rating to this day.

A tungsten filament GLS lamp designed for the notional harmonised
voltage of 230 cannot be sold in the UK and on the continent where
most supplies are using the 220v level since a lamp that lasts 2000
hours on the continent will only last 500 hours in the UK. We'd find
ourselves replacing lamps four times as frequently as our continental
neighbours.

There's a very good reason why lamps sold in the uk with 240v printed
on the envelope are _really_ 240v filamented lamps (and similarly in
the case of 220v lamps sold in most of continental Europe).

Modern electronically ballasted fluorescent lamps (both linear and
CFLs) and mains voltage LED lamps can be readily designed to cope with
such variations so can be sold with 220-240v voltage ratings. The good
old fashoined tungsten filament GLS lamp however, still has to work
within the constraints of 'Physical laws'.
--
Regards, J B Good