In article o.uk,
"Dave Liquorice" writes:
On Thu, 26 Nov 2009 08:35:59 -0800 (PST), Andy Dingley wrote:

It is a pity we are 'stuck' with relating brightness to wattage.
If we
used a proper definitive measure of brightness then manufacturers
would
have to be more honest.

Why? Would anyone still understand it? Are such complex topics taught
in school science these days?

The packaging of most (if not all) bulbs these days has a lumen
value. You normally have to look for it though normally on the energy
chart thingy or the bit that tells you the voltage and offcical base
type, B22 etc.

Actually, I do look, but it's often not there.
EU rules about labeling of lamps is going to change this.
IIRC, it is going to require the lumen output to be the largest
rating on the packaging. It will also require the energy efficiency
rating, but manufacturers have managed to get the requirement to
specify the power rating (Watts) removed. Apparently, we're all
being confused by power ratings on lamps. If the power rating is
still specified on packaging, it must be in a smaller typeface than
the lumen output. If it is not specified, it must be available on
the manufacturer's website.

Trouble is I don't know what 600 lumen compared to 700 is really
like, all I can say is that 700 is brighter. You can use the number
to do a better comparison between nominaly the same bulb though, one
"60W equivalent" against another "60W equivalent" CFL for instance.

Here's a table from an old manufacturer's datasheet, but GLS
lamps haven't changed much in decades, so probably still correct:

GLS, Coiled coil, 240v, 1000hr

Watts Initial Lumens Average Lumens
40 410 390
60 700 665
100 1330 1260
150 2160 2075

2000hr (double life) are about 10% lower.

Perl (frosted) used to be around 2% lower, when the frosting was
etched with hydrofluoric acid. Due to H&S issues with hydrofluoric
acid, perl bulbs switched to a powder dusting a few years ago,
and I believe this is less efficient, but I don't have a figure.
Softone, golfball, mushroom, and other decorative lamps usually
have a painted coating, and this loses something nearer 20% of
the light output, or even more if tinted.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]