On Tue, 25 Apr 2017 22:12:37 +0100, Johnny B Good wrote:
On Tue, 25 Apr 2017 14:27:29 +0100, Martin Brown wrote:
On 25/04/2017 13:27, Graham. wrote:
On Tue, 25 Apr 2017 12:25:35 +0100, "James Wilkinson Sword"
wrote:
Yes, I've googled it, but there are many different approaches. Which
one is used in domestic LED bulbs?
Ultra-violet LED exciting a white phosphor, much the same principle
used in florescents.
It is usually a high efficiency blue LED pump exciting a yellow phosphor
with that mix determining the nominal colour temperature. It is quite
peaky in the blue and more of a wide hump around the yellow. The
phosphor usually looks yellow and sits on top of the LED.
http://i.stack.imgur.com/lkyXG.png
The visible light flux out of an LED die on a high efficiency LED these
days is about the same order of magnitude as the sun's photosphere.
It is a lot more obvious on the devices which use a remote phosphor.
http://www.cree.com/led-components/m...e-Phosphor.pdf
An interesting read (note the use of the expression "loosing efficiency"
on page 8 regarding Fig 7a). Also of note is the copyright date of this
document which is the year of their record breaking 303Lm/W led efficacy
achievement in February/March of that year when the Cree Spokesperson let
slip to the trade press that such laboratory achievements typically took
a further 18 to 24 months of development before making their début on
store shelves for public consumption.
A simple arithmetic calculation reveals that this scheduled development
has slipped by a rather conservatively estimated 13 months. :-( The best
Lm/W efficacy figures I've noted recently have been around the 125 to 145
Lm/W mark. The former being a 1500Lm 12W GLS B22 2700K Warm White lamp I
sampled from a Home Bargains store for the princely sum of £2.99 which
turned out to have an *actual* consumption figure of 14 watts.
I thought the best LEDs were equivalent to 10W out per 1W in. Eg a 10W LED bulb should be equivalent to a 100W incandescent. A 100W incandescent is 1435 lumens. So your bulb is consuming 14W to give out about 105W.. Not as good as I thought.
Since its illumination power doesn't seem as impressively bright as I
was expecting (even making allowances for the eye's logarithmic response
to brightness), I rather doubt the additional 2 watts is hiking the
claimed 1500Lm to 1750Lms as one might expect if the additional 2 watts
was simply the result of overly wide tolerances in the 'electronic
ballast circuit' causing the LEDs to be overdriven to a higher than
designed Lumens output.
I have a sneaking suspicion that the claims of "1500 Lumens at 12W (100W
eqv)" have been based on the best of a sampling of these lamps off the
production line, possibly based on the maximum positive tolerance limit
of the 'nominal' power consumption to boot for good measure (+10%? =
13.2W) so might more typically be nearer the 110Lm/W mark than to the
claimed 125Lm/W figure. Even the claimed efficacy is not a particularly
massive improvement over the 81Lm/W efficacy figures typical of many LED
GLS lamps of just over three years ago.
Companies lie, they always do. Cameras state x MP, and if you take a photo at full resolution, it's ****. Hard disks don't use gigabytes, but billions of bytes, shaving off a little.
The 145Lm/W lamps I saw were the grossly overpriced 1600Lm LES 11W
examples being offered by Asda. I might have considered buying one if
they'd been more sanely priced but at something like 10 to 18 quid a pop
(I didn't bother trying to pin the confusing shelf price labelling down
any tighter than that - it was enough to know that it was at least 3
times pricier than I'd been prepared to pay in Home and Bargain), I
wasn't in the least bit tempted.
I'm currently using this sort of thing:
http://www.ebay.co.uk/itm/231644564446
Might not be the best price, I just linked to the first one I found, not where I bought them from.
The LEDs are well spaced and they don't exceed body temperature, so they don't fail like most LED bulbs.
It's not so much the electrical consumption cost savings that interest
me so much as the service life endurance promise standing a much better
chance of being fulfilled outside of a laboratory test environment in the
more demanding conditions typical of a domestic pendant light fitting
complete with fancy draught excluding shade dangling in the warmest
layers of air to be found in a room basking in the warmth of a centrally
heated radiator or two.
I'm happy enough with the current crop of "60W 806Lm 120v 750 Hour life
rated" American tungsten GLS lamp equivalent 9W LEDs where an 806 Lm lamp
can provide the required illumination level (effectively replacing a 73W
240v 1000 hour tungsten filament GLS lamp in UK housing). It's all these
15 and 18 watt 1500Lm LED GLS replacements for the 100W tungsten filament
GLS lamps with their more marginal temperature tolerance that give me
pause in their deployment as a GLS alternative.
The LED version of the "100W GLS tungsten filament lamps now starting to
appear would seem to be a viable GLS candidate if their claimed
efficacies of 145 and 150 Lm per watt are based in reality rather than
best hoped for efficacy.
It's been a rather disappointing wait for Cree to begin fulfilling that
(probably ill advised) promise made by their spokesperson just over three
years ago when they announced their record breaking achievement in LED
efficacy. Here we are, some 50 percent further along than their upper
timescale to get 300Lm/W lamps to market, with lamps of only half that
efficacy to show for their efforts thus far.
Still, at least *some* progress has finally materialised at long last,
so I suppose we ought to be grateful to finally be free of the 2013 'Time
Warp' we seem to have been living in for the past 3 or 4 years. :-)
Better late than never.
At this rate of development, we'll be lucky to see the next efficacy
milestone of 200Lm/W being achieved within the next three years or so.
Who knows? We may see a sudden spurt from Cree whereby the 200Lm/W
milestone in commercially available lamps is reached within the next 12
months. Either that or else an admission that the 303Lm/W lab results
were faked just to pressurise Philips Lighting into quitting the LED lamp
business. :-(
They really should put sensible ratings on each LED bulb they sell. It should clearly state the actual electrical consumption (it's been mentioned in this thread that they lie), and equivalent output (eg "=60W incandescent". The general public don't know what a bloody lumen is.
--
I took a vow of faith, I don't shoot any more.
You don't shoot any less either.
-- Machete, film, 2010.