LED light bulbs?

[xortam]

I'm very unimpressed with CFL, or at least the brand that I recently bought. I put two in a four bulb fixture along with two incandescents and the CFLs didn't even last six months. I don't know if mixing bulb types could have caused the problem, but I doubt it. We'll see how the single CFL installs of the same batch do.

[Dr Mordrid]

And you're going to see lots of LED headlights in cars soon, especially in PHEV's and EREV's like the GM E-Flex cars (Volt etc.). GM and others are putting a lot of effort into watt-trimming in several areas; electronic systems, wipers, lamps, HVAC (going CO2 cycle there) etc. etc.

Know anyone in Hawaii? Word is the big island will be getting 200 Chevy Volts soon after release.

Also: Volt hits design freeze in 4-5 weeks.

[Jammrock]

http://www.raleigh-nc.org/portal/server.pt/gateway/PTARGS_0_2_396_208_0_43/http%3B/pt03/DIG_Web_Content/news/public/News-PubAff-_LED_City__Results_In_Sa-20070710-09463246.html

http://www.news.com/2300-11392_3-6158011-1.html?tag=ne.gall.pg

[Brian Ellis]

It is not true that modern (HF) CFLs require high start-up currents. The older ones, using an inductive ballast, yes (they had a very weighty base).

OTOH, frequent on and off cycles will reduce their life because the cold cathode system requires a short starting pulse of ~400 V to prime the ionisation and this tends to deteriorate the cathode surface. It is not really the short on period, but the number of times the lamp is started, no matter how long it is on for. Makers typically state a 10,000 hour lifetime, but this is based on the phosphor poisoning reducing the light output, but the number of start-ups can vary from 5000-15000, depending on the internal design. As a general rule, the cheaper bulbs have a shorter no. of start-ups.

The rule of thumb is that they are perfectly usable in cluggies with intermittent use but do not switch them off if you want light again within a minute or two.

[Fat Tone]

Yes. They said the break-even point on flourescent tubes was 11 seconds. Far less than you would think.

[Mehen]

I have been using CFL's for years(actually more like a decade) in most of my fittings.

One problem CFL's have had is the startup energy required, eg if you are only going to put a light on for a couple of minutes then incandecent is more efficient.

So with scenario in mind, I don't use CFL's in places where the light is turned for a small amout of time.(eg toilet)

Has that behaviour improved?, years ago I was told if the light is on for less than 10 minutes at at time stick with normal globes.

Though I guess LED fitting would be the ideal for this situation.

I think the Mythbusters did something on this.

[Marshmallowman]

I have been using CFL's for years(actually more like a decade) in most of my fittings.

One problem CFL's have had is the startup energy required, eg if you are only going to put a light on for a couple of minutes then incandecent is more efficient.

So with scenario in mind, I don't use CFL's in places where the light is turned for a small amout of time.(eg toilet)

Has that behaviour improved?, years ago I was told if the light is on for less than 10 minutes at at time stick with normal globes.

Though I guess LED fitting would be the ideal for this situation.

[Brian Ellis]

Of course FAR more GaAs is used in electronic circuits like TV's, computers, IC's, solar cells and multimedia devices than in LED's. Unless it's ground into fine particles (as in a polishing process) GaAs is relatively stable; you could eat a chunk and not absorb enough As to do damage.

True, but not in a landfill at end-of-life. It is known that As levels in leachates have increased in some landfills, possibly due, at least partially, to the presence of numbers of EOL cell phones, which use GaAs semiconductors for the HF circuitry. Heavy metals, such as As and Pb in leachates are usually fixed by iron oxides in the surface layer of soil/rock they encounter, so the water becomes harmless. However, it is becoming apparent that this ion exchange mechanism is inhibited by the bacteria found in landfills and there is a growing real concern appearing of arsenic contaminating ground water, used for potable supplies. There is ongoing research conducted in several countries. Of course, I emphasise that GaAs is not the only potential source of As in landfills: pesticides and old building demolition may also contain it.

GaAs semiconductors are rarely used except where some specific quality is required, because they are much more expensive than Si or Ge. They have an electron mobility about 3½ times greater than Si and a hole mobility of ~2x greater, combined with a fairly similar bandgap. Their temperature characteristics are poorer than Si. I have no definitive figures but my guess is that about only 1-2% of semiconductors are GaAs and the rest, the massive majority, are mostly Si with a few niche contenders for really specialised applications. I mention this, because you imply that they are much more widely used quantitavely than is the case.

[Brian Ellis]

Try explaining that to someone with a migraine.

I agree that hot cathode fluorescent tubes with a conventional inductive ballast do flash on and off 100/120 times/sec. The modern CFLs do not because a) they are cold cathode and the ionisation of the gas, which does include a truly minute amount of mercury vapour (if it were condensed into a droplet of liquid mercury, you would need a powerful microscope to see it), is achieved by HF excitation, so it does not flicker at the power frequency and b) the modern phosphors have a long persistence so that they continue to glow for much longer than the 10 ms needed to bridge the gap. Early CFLs did flicker slightly but the technology is now well advanced to prevent that with the latest generation.

[Dr Mordrid]

Of course FAR more GaAs is used in electronic circuits like TV's, computers, IC's, solar cells and multimedia devices than in LED's. Unless it's ground into fine particles (as in a polishing process) GaAs is relatively stable; you could eat a chunk and not absorb enough As to do damage.

Arsenic aside; a lot of LED's for lighting will likely be OLED's, which use organic dyes as an emitting material. More colors, can be "printed" on to polymer substrates and formed into most any shape and with the newer PLED's have a life of 198,000 hours.

[Umfriend]

I happen to have one of those at home. Never a prob with flickering CFLs

[TransformX]

Try explaining that to someone with a migraine.

[Wombat]

You all forget people with migraines. Flickering light is the devil, no matter how fast it flickers.

CFLs with the latest ballasts don't "flicker" any more than anything else you can get. Incandescents run off of the house wiring, so they're "flickering" at 50/60/whateverHz as well.

[TransformX]

You all forget people with migraines. Flickering light is the devil, no matter how fast it flickers.

[Brian Ellis]

T8 fluorescent, by a long chalk, but not very elegant. For practical room lighting CFL wins hands down. LED wins only for small area lighting, e.g., benchtop.

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