On Wed, 26 Mar 2014 15:08:06 -0700 (PDT), wrote:

On Wednesday, March 26, 2014 5:01:00 PM UTC, Johny B Good wrote:
On Wed, 26 Mar 2014 15:14:08 +0000, Timothy Murphy wrote:
Martin Brown wrote:

I was a bit surprised to see when I visited IKEA recently
that the LED "candle bulbs" were slightly less efficient,
in lumens per watt, that the more standard energy-saving bulbs.

That's typical. What you're paying for (assuming enough lumens) is
the 50,000 hour life rating and 'instant on' feature.
The best lighting in terms of cost per lumen output still remains the
linear fluorescent tube in an electronically ballasted fitting.
The CFL can't compete simply on account that its much higher tube
temperature demands the use of the slightly less efficient mercury
amalgam fill (the reason why they suffer a 'run up to temperature'
delay in reaching their design lumens brightness).

I thought short tube length was the main cause of lower efficacy.


That's certainly a contributary factor (possibly the main factor) but
it's surprising just how long the coiled tube turns out to be in a
modern 11W CFL. I've just checked one and I reckon they've packed a
good 14 to 15 inches worth of tube, not counting the hidden ends, into
the double helix.

Without hunting down a 20W example to measure, I reckon the effective
tube length could be approaching the 20 to 24 inch mark, significantly
longer than the classic 6 and 8 inch linear tubes where the short
length is a major factor in reduced efficacy.

One thing I do know for a fact is that the mercury amalgam lamp is
less efficient than the straight mercury vapour lamp when each is run
at their optimum temperature. I'd overlooked the short tube effect on
efficacy so there's even less reason to disbelieve that a modern
linear tube and electronic fitting is the most efficient of all the
GLS lighting technologies to date.

Given further development of the LED lamp, notably more efficient
mass production as demand starts to increase to scale up mass
production to more economic levels, the price of such lamps will fall
to a level comparable to the equivilent of the 5 or 6 CFL lamps it
replaces. The efficiency needn't have to match or exceed a modern CFL
to succeed as a replacement since there are other benefits than just
the bare watts to lumens ratio involved in the TCO equation.

At the moment, most LED lamps are around 4 to 4 1/2 times more
efficient than a tungsten filament GLS lamp compared to a CFL's
efficiency figure of 5 times. An LED lamp isn't so far behind the CFL
and may yet match or even just exceed the efficiency of the CFL in the
not too distant future.

As things stand, it's not the slightly lower efficacy compared to CFL
that's holding back the uptake of LED. It's the high price on GLS
lamps with barely adequate ratings that's the big turn off.
--
Regards, J B Good