In article ,
"dennis@home" writes:


"alexander.keys1" wrote in message
...
On Jul 12, 12:57 pm, Scion wrote:
The Argos catalogue has lampshades with different ratings for
incandescent
and CFL lamps. e.g. Rated for 60W incandescent or 12W CFL.

What's that all about - I thought the rating was to prevent overheating
and
therefore the rated wattage would be about the same regardless of the
type
of lamp.

Is it me missing something obvious or is it the Argos catalogue compilers
automatically converting one to the other?

It's because of the heat emitted by the bulb, not the current drawn,
the heat production is equal to the wattage for whatever type of bulb.

You have to be careful when you look at the ratings..

a long time ago the rating would be the maximum for a tungsten bulb and
would limit the temperature to a safe value for the *shade* (so it didn't
melt or burn) the lamp could run at near the melting point of the solder on
the base or higher if it were a capsule lamp with no base.

GLS (bog-standard filament lamps) are designed to run up to 200C.

The same is true for a CFL, you could go to the same wattage and the *shade*
would be safe.

However CFLs will not run at the temperature that tungsten bulbs will and
can overheat in some shades even when they are well below the rating for the

Retrofit CFL tubes are generally designed to run around 80-100C.
The electronics in the lamp base may be a little cooler, but since
they only have to last about 10,000 hours, the fact that they're
running near boiling point is just about viable. Each 10C temperature
rise generally halves the life of electronic circuits, so if you
operate it in a poorly ventilated fitting and it runs at 20C hotter
than it would in open air, the reduction to only 1/4 of the life
means that you'll probably start seeing some CFLs die due to ballast
failure before the tube wears out, and not realise the expected design
life across a reasonable sample size.

shade. The same is true for LED bulbs even though they are only a few watts.

LEDs have additional problems. They are destroyed at lower temperatures
than silicon semiconductors you'll find in a CFL ballast, so they have
to operate at lower temperatures. Secondly, they _are_ the source of heat
(whereas in a CFL, the tube is the source of heat and some separation
from the heat sensitive ballast can be achieved). Thirdly, the light
output (and efficiency) of most (if not all) LEDs drops dramatically
as they warm up, which makes being a source of heat a double whammy.
Turning a raw LED into a usable light requires significant thermal
design.

In general I avoid any shade that blocks ventilation, not doing so seriously
reduces the life of CFLs and LEDs.
It may be that argos are checking what is OK for CFL in each shade but I
doubt it.

--
Andrew Gabriel
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