On Sat, 29 Nov 2014 14:23:55 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
Thought that was to allow a CFL to achieve full level on a cold day? ;-)

I saw the smiley but Andrew was referring to the fact that a low
pressure mercury vapor discharge fluorescent tube starts off at around
a 110% of its 'design lumens' before swiftly dropping down to 100%
during the first thousand hours or so of an 8 to 16 thousand hour
design life when the output will have dropped to something like 80%
before the drop is considered to be end of life.

Very true. However, my limited experience of mains LEDs is they never get
anywhere near their claimed life before failing. And they are more costly
than a CFL.

That's very true in regard to their regular pricing. My experience is
probably a lot more limited than yours in regard to lamp life.

I've only bought two during the past year, a 5W 270 Lumen BC
'classic' shape 'bulb' for a fiver last year and a 12W 810 Lumen
'bulb' for £3.49 earlier this month, both from our local Asda
Superstore as it happened.

I suspect the 12W lamp has already clocked more hours than the 5W
lamp simply because I eventually installed it in the basement landing
area in a ceiling batten fitting just by the electric meter where it
probably never sees more than half an hour's use per week on average.

Since that 5 watter is operating in the coolest part of the house,
unencumbered by any form of lamp shade, it stands the best chance of
living up to the maker's 25,000 hour life rating claim. At the current
usage rate, there's every chance I'll be dead and cremated before it's
clocked its first thousand hours. Even if I decide to leave it running
24/7, it's going to take nearly 3 years before it reaches the 25000
hour mark.

The 12W lamp, otoh, is probably going to average 4 to 6 hours a day,
roughly 6 months per 1000 hours of lamp life. Assuming 2000 hours a
year usage, that's a 12 year lifetime based on a 25000 hour life
rating.

Thus far, I've not experienced any premature mains voltage LED lamp
failures (but it's _very_ early days and a sample size of only two
lamps).

Let's face it, with such extended life claims, any failures within 2
years of purchase are a guaranteed indicator for premature failure
even if the lamps in question where left permanently lit after being
installed.

Only this afternoon, I was in the "Home Bargain" shop with the
missus, contemplating increasing the sample size to 3. I was looking
at a 7W 620 lumen BC example they had on the shelf for £4.99 (same
efficiency level as the 15 quid 810 lumen 10W LES lamp in our local
Asda superstore).

In the end, I resisted the temptation based on my feeling that I
would be joining the "Early Adopters'" club and paying a premium price
for the priviledge.

A year ago, I would have snapped it up (and the other remaining BC
example out of a pile of LES lamps) at that price but, ever since
purchasing that 12W 810 Lumen lamp at the beginning of the month in
Asda for a 'mere £3.49', my LED lamp bargain price point reference has
now slid down to a new low.

I'm older and wise enough to know better than to play that game of
"Early Adoption" to start over-investing in an immature technology
that still has a few more years to go before it hits the limits on
efficacy and mass production led pricing levels. I've still got an
ample supply of CFL 'spares' to see me through the next couple of
years so I can afford to play the waiting game. :-)

However, that won't stop me being on the look out for more LED Lamp
Bargains. It's one thing to blow 3 or 4 quid on a single LED bulb but
another one entirely when it comes to replacing the ten 7W SES CFL
candle lamps in our two chandeliers at a price of £3.99 each to the
tune of 10p shy of a 40 quid investment in the 7W LEDs currently on
the shelves of Home Bargain.

I've no doubt that in a years time I'll be seeing 5W versions of
equal or higher brightness SES candle lamps a quid or two cheaper.
Others might argue, as they often have with computer technology, that
there'll always be a better value product on the horizon and you face
the risk of your purchase becoming dated or worse still, obsoleted no
matter how much you delay. That's a valid argument for Personal
Computers and all the spin off technoligies (smartphones, tablets etc)
but not so for something like a more efficient lamp which has definite
and well defined limits on its performance.

From the press releases issued early this year by Philips and Cree we
can expect to finally see real product on the shelves in another 12
months time with triple the efficiency of the CFL (or only double that
of an electronically ballasted linear fluorescent tube) at which point
the manufacturers will be well and truly into 'Diminishing Returns'
territory.

Next year's "Early Adopters" are not going to have their smug smiles
of satisfaction wiped off their faces as swiftly as today's early
adopters when the next round of lighting technology development makes
its appearance.

I reckon that in about 12 months time, we'll have reached that point
where the returns on running costs will finally justify the capital
investment in LEDs with a very much reduced obsolescence risk factor
to boot.

There will no doubt be better lamps available in the years succeeding
next but the improvements will be more marginal than we know is the
case today. Furthermore, the pace of such improvement will be slowed
right down to a snail's pace compared to what we've witnessed during
the last 5 years or so (and promised over the next 12 months).

By all means, snap up those odd bargains you might see from time to
time where you know exactly where you're going to usurp an existing
CFL or even an incandescent lamp to maximum benefit (but I'd hold off
on a mass LED upgrade for another 12 months if I was you).


Incidently, it's just occurred to me that your problem of premature
lamp failure could be due to overheating. Unlike tungsten filament
lamps that can and do run at 200 degrees and higher temperatures in
conventional lamp fittings which allows them to dissipate their 60
watts of waste heat with ease, LEDS are limited to a much lower
maximum temperature (80 to 120 deg C ?) and can overheat in poorly
ventillated fittings rated for 40 and 60 watt incandescent GLS lamps,
especially when the lamp is burning cap up.

It's a limitation that's not so apparent when the lamp is quite
obviously meant to be a "Drop In" replacement for the good old
fashioned tungsten lamp. The thing to look out for is a lack of
ventillation such as happens with some lamp shades and pendant
fittings. Such fittings result in a nice cosy blanket of hot air
surrounding the base of the lamp where the electronic ballast
components live (or die).

The later more efficient lamps will be less prone to this overheating
hazard since they generate less waste heat per lumen of output. This
is one of the main factors that limited the earlier lamps to quite
modest lumen ratings. It's only now that we're starting to see lamps
with more useful outputs of 810 (and even higher) lumens (60W American
/ 75W UK GLS filament lamp types). This yet another good reason to
hang back before 'blowing your wad' on a whole house relamping
upgrade.
--
J B Good