8 Apr
2011
8 Apr
'11
10:56 a.m.
On 08/04/2011 17:34, Jules Richardson wrote:
Dave's mention of 100W of light for 12W of power is way off. I'm not
sure he believed that, but it's not far from what some manufacturers
have claimed. The truth is that a typical /new/ CFL will give an
improvement of at best about 5:1 (equivalent of a 100W incandescent from
a 20W CFL) and the light output drops a lot over time. That's why over
here manufacturers are now supposed to quote the light output rather
than the equivalent wattage, and if they make comparisons are supposed
to also state the light output of whatever incandescent they're
comparing it to. I doubt many consumers have much clue about light
output numbers, though.
Wikipedia says over the life of a CFL the output drops to typically
70%-80%. My own measurements say it's much worse than that, and I've
had to replace CFLs that emitted less than 50% of their original output.
Chuck Guzis wrote:
Me too. Particularly when a lot of it is done under
the guise of "saving
the planet", and it's not at all clear that CFLs do that when the bigger
picture beyond point-of-use is taken into account.
True, there's a lot of nasty stuff used in making CFLs, more than in
incandescents.
a manufacturer
who will *guarantee* (not pro-rated either) 5000 hours
of trouble-free illumination from a CFL and I'll bite.
... and that they're not lying about the "equivalent wattage" ratings,
and that the illumination that it gives is of a
reasonable quality
rather than having a sickly color-cast to it.
It's possible to get "daylight" CFLs that are better if a little more
expensive, and it's possible for a premium price to get ones that have
an almost continuous spectrum, as needed by photographers. But most
"daylight" ones, even ones sold at twice the price of "ordinary" CFLs,
have a pretty awful colour balance and a lot of gaps in the spectrum.
You can see the effect on some artificial dyes on artificial fabrics,
which can actually look a completely different colour (not just a
different shade) between daylight and CFL light. Nightmare for
graduation pictures (I had to re-shoot a whole set once because the
hoods on some gowns came out gold instead of green).
Worst of all (for a photographer) is that different brands can have
different phosphor mixes and need radically different correction filters.
Over here CFLs are required to be marked (at least on the packaging)
with a colour rendering index number that denotes how "good" they are on
a scale of 1-100. Most score 60 or so. Some "daylight" ones score
between 70 and 80. Really good ones score up to 90. Incandescents
easily score 100.
--
Pete Peter Turnbull
Network Manager
University of York