Re: Long life lights

On Mon, 1 Sep 2008 03:03:02 +0000 (UTC), don@xxxxxxxxxxxxxx (Don
Klipstein) wrote:

In article <opdjb4tfqpjptb517apn9fv8i6hk12gfot@xxxxxxx>, JosephKK wrote:
On Sun, 24 Aug 2008 13:27:49 -0500, "Tim Williams"
<tmoranwms@xxxxxxxxxxx> wrote:

I've got a problem. I happen to carry the distinction of being the one
responsible for changing lights. Much as that's a problem in itself, the
biggest problem is.....the front porch light (surprisingly, it's not a
stairway light, eh?), which happens to be a hanging, upside-down, enclosed
fixture. And they put two screws in the thing, so it's almost impossible
for a single person to replace the bulb thus inserted. Really quite
remarkable how no one thought of this.

Besides modifying it, which I may consider because it's just that bad, in
the mean time I need something that'll last. We've already tried the "ten
gajillion hour" CFLs, which died in all of, you know it, three months. I'm
guessing something high voltage (130V+?) and incandescent. Any
recommendations?

They are still expensive as heck, but you can get LED lamps. Perhaps
below US$50 each for 100W equivalent, but always over 30,000 power on
hours life and some (more expensive) are rated at over 100,000 hours
power on.

Buyer beware for life expectancy of LED "lightbulbs" and the like,
especially if they are white ones.

100,000 hours is a widely-repeated number, to the point of
"conventional wisdom".

White LEDs often fade significantly well before then - I dare to say
they mostly do. Colored LEDs, on the other hand, appear to me to have
most operated for 100,000 hours or more to be keeping on trucking
rather well after working for so long.

Most of your sloppily called "colored" LEDs are standard monochromatic
LEDs. They are cheaper to manufacture that way.

White LEDs are for most purposes are a variation of fluorescent lamps.
(no Mercury content though)


It appears to me that better heatsinkable white LEDs take 50,000 hours
to fade by 30% at "characterizing current" ("typical current") when
heatsunk to what I call a "moderately conservative extent". Much longer
life expectancy as in 100,00-plus hours appears to me reasonable if they
are both significantly underpowered and heatsunk to extent to keep the
junction temperature well below the "old traditional" maximum recommended
LED junction operating temperature of 85 C. In general, LEDs are more
efficient when cooler and most blue, white, and non-yellowish-green ones
are more efficient when moderately or moderately severely underpowered -
even regardless of temperature.

One of the best reliability engineers i ever met liked things "nicely
derated". 3 W white LED, run it at 1W, you will like the life
improvement. Now, of course, time cost of money and time cost of
devices will interfere with this.


A main difference between white LEDs and most colored ones is that white
LEDs normally have a phosphor and over 99.9% of colored ones I have seen
don't.
The few colored LEDs that I have seen with phosphor are pastels, pink,
lavendar/"purple" (as opposed to "violet", which is nearly-UV or an
indigo-bluish-violet color with some "blacklight" effects), or a
non-amberish maybe-slightly-chartreusish yellow close to 255-255-0 on a
usual monitor.
Also beware - violet and UV LEDs with epoxy bodies tend to age fast due
to UV or nearly-UV being hard on the epoxy.

And it still surprises people.


I have seen sone reasonably credible numbers for even better 5 mm /
T1-3/4 LEDs to fade significantly (don't know whether by 30% or 50%) in
as little as 6,000 to 10,000 hours. I don't know whether this is at
"characterizing current" of 20 mA or at maximum current of 30 mA. Some of
this is news years old and some I got more recently.

One model of a white LED nightlight that I tried had "half-life" close
to half a year. I would prefer green or blue LED nightlights over white
ones for better life expectancy as well as having a spectrum more
favorable for stimulating "scotopic vision" ("night vision").

Good point, a lot of people still miss this one.


- Don Klipstein (don@xxxxxxxxx)
.

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