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The Natural Philosopher

pete wrote:
On Tue, 11 Nov 2008 05:53:59 -0800 (PST), wrote:
The packaging is another example of marketing 'though. It claims the
11W is equivalent to 60W, and even gives a comparison of a 60W
incandescent providing 620 Lm, and itself offering 640 Lm. The only
problem with that is that a standard 240 V GLS 60W (Frosted) gives
700 lumen, and it is the so-called 'softlight elegance' that offers
only 620 lumen.

After the initial discussion here about the brightness of these bulbs
I did some real-life tests. The setup was a sheet of A0 white paper
(from a flip-chart) laid flat on a table underneath a ceiling hung
light fitting with a lampshade. I pointed my DSLR at the paper and
noted the exposure timing. All other parameters remaining constant.

With a "normal" 60W pearl bulb the exposure meter reported 1/90 sec.
With an 11W CFL, the meter said 1/60 sec.
With an 8W CFL the meter also read 1/60 sec.

While I'm only looking at _relative_ measurements, and I was concerned
only with light for reading by (hence seeing what was reflected off the
paper), it supported my view that CFLs were dimmer than tungsten bulbs.
The interesting result was that 8W bulbs threw just as much light in
a downwards direction as the 11W bulbs. I reckon this is because the
light is projected downwards off the end of the bulbs, not off the
body. Since 11W bulbs have longer bodies, but the same x-section, the
usable light output is the same. The sideways emitted light is largely
absorbed by the lamp shade (hence it's name!), even though it had a matte
white interior.

Now I'm quite happy to accept the manufacturers' claims that the absolute
light output, measured in laboratory conditions, is similar to tungstens.
However, I have convinced myself that in a normal domestic ceiling-hung
fitting, the shape of the bulb reduces the amount of usable light by far
too much.

Thats is fairly consistent with my findings as well. an 11W spiral is
similar to a 40W bulb. The longer things are a bit better, especially
sideways. I have some in some outside lamps where light comes out more
sideways, and there they are close to a 60W.