A female friend has just bought an expensive pendant light fitting
which on examination has cable which I would rate at a minimum of 3,
more like 5 amp, and a brass / ceramic bulbholder.
The box clearly states 'Max bulb size is 60W halogen or 11W CFL.'
Please tell me they're being a tad over cautious. She wants to fit a
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I think the rating has more to do with heat dissipation than cable size.
Too high a wattage bulb could lead to over-heating. I wouldn't go over 60W
Regarding CFLs, I think the rating are a bit idiotic. Certainly they won't
put out as much heat for a given light output and the figures quoted are
always for light output "equivalence" (rather than heat) even if we all
know that the ratio in real life is much more like 4:1 than the oft quoted
That said, a "wrongly" rated CFL in the fitting may overheat its
electronics leading to shortened life, even it it never actually risks
being a fire hazard so it probably wouldn't be wise to assume that you
could use a 60W CFL.
I have just bought a couple of not-too-expensive pendant lights for
our kitchen, with metal shades, and a rating of "42W or 11W energy
saver, shape GLS". I assumed the heat was the limiting factor, although
it would be nice if there was some explanation.
Of the available lamps nowadays, CFL, Halogen, LED, which produce the
most and least heat for a similar light output, and how do they
compare with the baseline of an incandescent?
Maybe I can drill some ventilation holes in the top of the shades to
increase their effective rating.
Filament produce the most heat (least efficient).
CFL are in the middle.
LED produces least heat (most efficient).
However, it's not as simple as that.
Filament lamps normally run at 200C bulb temperature,
CFLs at 100C tube temperature,
and LEDs have to run cooler than both those.
So to a rough approximation, if a fitting can take a 100W filament
lamp, it will only manage roughly same equivalent light output from
the other technologies, i.e. 23W CFL, and probably less than 15W LED.
If you put a 100W LED in there (supposing one existed), it would
probably die in a few minutes.
For filament lamps, temperature rating of the lampholder is also
a factor. A 100W bulb normally needs a class T2 lampholder which can
run at over 200C, whereas a 60W bulb can get away with a lower rated
T1 lampholder which can't run at 200C.
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Compare Lumens and see what is the max Lumens you can get. I have a bulb
that claims to be 100watt equiv but is a 75 watt QI bulb inside a larger
Some interesting LEDs now getting into the shops but you need to target
Lumens to get a deent comparison.
I was in Morrisons yesterday, looking at their big display comparing
the different bulb types, and Lumens was the one item that was not
listed for comparison! That display has always annoyed me by having a
big spread purporting to let you choose exactly the bulb you need, and
then not having it in stock.
A shame we don't have a real electrical shop in town, it's a
choice between Morrisons and Tesco, neither of which I trust anyway.
supermarkets, even big ones, don't have a very good range.
DIY sheds are pretty good, our small B&Q has a pretty good range (of
course it's getting harder for them to carry the full range, as the
number of different bulbs has grown - still lots of incandescent bulbs,
CFL and now LED, and the various bases. so they don't always have quite
the combination you want.
But I tend to get most of mine online nowadays.
No DIY sheds here, the nearest B&Q and Wickes are 20 miles away or
so. The only DIY place closed down a year or so ago. I think online is
the way to go. Any recommendations for a good supplier? I use CPC
often, and occasionally 7dayshop, but haven't yet investigated their
On Fri, 7 Nov 2014 00:15:02 +0000 (UTC), email@example.com
(Andrew Gabriel) wrote:
Is a good question. It's not as easy to answer as a simple wattage
comparison might suggest.
Efficiency for a tungsten filament lamp is circa 5% (not the worst
transducer efficiency - moving coil speakers are typically only about
a fifth as efficient!)
Typically reckoned to be some 4 to 5 times more efficient, circa 23%?
Only the more recent designs available in 7 watt or higher ratings
over the last 12 months or so. The earlier designs have only been
about 4 to 5 times better than incandescent (similar to CFL with
earlier designs not even being as good as that). The recent 10 to 12
watt 810 lumen lamps that have only recently arrived in the likes of
Asda at sub astronomical prices, are only now offering 6 fold or
higher improvement over incandescent.
I recently picked up another 'bargain LED lamp" in our local Asda, a
12W 810 Lumens LES classic pear shape envelope for a mere £3.49 off
the 2 quid shelf. This was an even better bargain than my previous 5W
370 Lumen BC 5 quid bargain just over a year ago. The slightly more
efficient, otherwise identical, 10W, 810 Lumen lamp on the shelf above
was a whopping 15 quid!!!
It just so happened that we have an Ikea adjustable pendant lamp
shade LES fitting over the dining table crying out for a better lamp
than the 20W CFL it had been sporting for the past 5 or 6 years. A
lamp that started up a very dim pink for the first 5 or 6 seconds
before turning a dirty white increasing to full brightness over a
further half minute period of run up time.
The shade is a painted aluminium chinese hat styled affair with no
vent holes, rated for a 60W incandescent lamp. The lack of vent holes
is mitigated by the larger than normal air volume due to the very
shallow angle of the reflector to increase the effective conductive
surface for the volume of heated air that surrounds the cap end of the
lamp. It's not ideal but a damn sight better than most other unvented
BTW, the 12W LED is just noticably brighter than the 20W CFL it
That's the thing, no fragile electronics in the cap to worry about.
Hence the requirement for an amalgam filling and the protracted run
up time to reach an efficiency only a few percent lower than a
straight low pressure mercury vapour as used in conventional tubes.
Yes, the electronics (which includes the LED(s) in this case) are
limited to the sub 150 deg C range, in practice limited to about 100
deg C. It's this lower temperature limit that determines the maximum
waste heat dissipation wattage rating for both CFL and LED lamps. A
good approximation to a 60W incandescent lamp rating for CFL and the
current LED lamps would be a 15 to 20 Watt max.
That can prove very beneficial to a LED (or a CFL) lamp where the
reduction in running temperature can have a dramtic effect both on
efficiency and (especially true for a lamp intended to last 8 to 30
thousand hours as opposed to a mere 1000 hours of a tungsten lamp)
A T2 lamp holder would be wasted on a CFL or LED lamp. A fitting
designed to cope with a 150W incandescent lamp is unlikely to allow
any greater wattage ratings of LED or CFL to be used compared to a
fitting designed only to cope with a 60W incandescent lamp.
However, One overlooked side effect of upgrading from a 22% efficent
12W 810 Lumens lamp to the latest 45% efficient 15W 2025 Lumens lamp
in another year or so's time is that the waste heat of the 15 watt
lamp will actually be about 1 watt lower at just over 7.5 watt (about
a twentieth of the dissipation of its 150W tungsten equivilent).
The latest LED lamps now available in the 7 to 12 W range at sane
prices (sub 5 quid a pop) are now efficient enough that they can be
used as drop in replacements for sub 100W incandescents into most
fittings without concern for overheating issues. Give it another year
or so and the issue of overheating will have gone away for all but the
most unusual of lamp fittings.
As far as LED lamp technology is concerned, "We Live In Interesting
Times". Take care not to be conned into buying prematurely into the
(until recently) myth of LED lamps being more efficient than CFLs,
especially in stores like Aldi and Lidl.
A lot of retail outlets are too busy clearing out the 'barely better
than CFL efficiency' stock from the distribution channel right now. I
reckon it'll take about another 12 months before we start to see
competitive pricing on the latest"Ten times more efficient than
incandescent" LED lamps appearing on the shelves.
My last one came from CPC and they were fine - and have the advantage of
My last ones (CFL) came as part of an order from CPC, they seem fine.
They have the advantage of only needing to spend £10 for free delivery
I've used BLT a few times, were fine.
someone else as well, but forget who they were right now.
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