CFL and LED Bulb lifetimes in partially and fully enclosed fixtures

[slebans]

A short but interesting article. Of particular note is the 3K hour estimated lifetime for a CFL bub in the base up position. Also, I had no idea that temps could reach such high levels in a semi-enclosed wall sconce.

http://www.ledsmagazine.com/article...pends-on-fixture-type-and-usage-scenario.html

 

[Steve K]

Nice to see some actual numbers, instead of theorizing about what happens in an enclosed fixture.
As long as the market is aimed at replacing incandescent bulbs in existing fixtures, instead of designing fixtures with built-in LEDs and intrinsic heatsinking, we'll be dealing with this situation.

for semi-enclosed fixtures, the only solution that comes to mind is to build a LED bulb with a small internal fan. It's going to increase the price, but hopefully it'll be balanced by a greatly increased lifetime.

 

[tel0004]

One thing to keep in mind is that LEDs have the potential to double in effeciency, which will mean less heat output.

Design a 60 watt equivalent LED that only uses 5 watts of electricity and build it well enough to last 5-10 years an an enclosed fixture and sell it for 5.00 and I dont think the market will care that it doesnt last 20 years like a bulb in an open fixture would.

I would bet we will see plenty of 5.00 led bulbs in the next 5 years, and the effeciency should be possible in 10.

I can pick up phillips LEDs for 5.00 today (subsidized by the power company)

 

[LEDninja]

Back when LED bulbs were $50+ the claimed life was 50,000 hours.
When the bulbs were/is down to $15 - $30 the claimed life was 30,000 hours.

When the new Philips slim style BR30 got reviewed the claimed life is 3000 hours.
http://www.candlepowerforums.com/vb/showthread.php?389640-Philipis-BR-30-quot-Slim-Style-quot-LED
That is in free air. In partially and fully enclosed fixtures it will be a lot less.

There is also a trend towards 100W equivalent LED bulbs which would push heat production and management to its limits.

 

[mattheww50]

With CFL's it is possible to use a magnetic ballast, and those ballasts almost don't care about temperature. Unless they get somewhere the Curie Point (typically several hundred degrees C), they are going to work just fine. Most high efficiency CFL's use electronic ballasts, and unfortunately they do care about temperatures, and suffer both performance and lifetime issues from operation at elevated temperatures.
LED's are even worse in that respect. About a year ago I tried replacing some 50 watt Halogen GU10 lamps with 9 watt LED replacements in an enclosed fixture. The LED's got so hot they melted the plastic lenses they were behind. Within a couple hundred hours, they were all effectively dead. Until LED efficiency gets a lot higher (and a doubling in LED efficiency changes the heat output from 85% to 70% of the input energy, so doubling the efficiency will make a big difference in light output, but not a huge difference in the heat dissipation requirements), or somebody finds a better way to dissipate the heat generated, LED lamps in fully enclosed fixtures are going to have problems.

The reduction in life expectancy of the LED bulbs is an admission of the heat dissipation problems. Each 10 degrees C the operating temperature goes up (18 degrees F) will essentially halve the life of the device, or in the case of philips, perhaps an admission of other problems. My early experiences with Philips CFL's were they didn't reach 10% of the claimed life, and they weren't even in enclosed fixtures!

 

[dragonballz]

I just replaced a CFL bulb with an LED bulb. Holy crap does the base get hot. The glass bulb part only gets slightly warm but the base almost gets as hot as an incandecent. Hotter than the CFL. Makes me wonder how it can be so efficient...

 

[SemiMan]

With CFL's it is possible to use a magnetic ballast, and those ballasts almost don't care about temperature. Unless they get somewhere the Curie Point (typically several hundred degrees C), they are going to work just fine. Most high efficiency CFL's use electronic ballasts, and unfortunately they do care about temperatures, and suffer both performance and lifetime issues from operation at elevated temperatures.
LED's are even worse in that respect. About a year ago I tried replacing some 50 watt Halogen GU10 lamps with 9 watt LED replacements in an enclosed fixture. The LED's got so hot they melted the plastic lenses they were behind. Within a couple hundred hours, they were all effectively dead. Until LED efficiency gets a lot higher (and a doubling in LED efficiency changes the heat output from 85% to 70% of the input energy, so doubling the efficiency will make a big difference in light output, but not a huge difference in the heat dissipation requirements), or somebody finds a better way to dissipate the heat generated, LED lamps in fully enclosed fixtures are going to have problems.

The reduction in life expectancy of the LED bulbs is an admission of the heat dissipation problems. Each 10 degrees C the operating temperature goes up (18 degrees F) will essentially halve the life of the device, or in the case of philips, perhaps an admission of other problems. My early experiences with Philips CFL's were they didn't reach 10% of the claimed life, and they weren't even in enclosed fixtures!

Time to get into the 2010's on LED tech. Current heat output is well less than 85%, try 65% on the best bulbs today. Doubling that gets to 32.5%, but since you have 1/2 the power, it is actually 16.25% of the original. As well the LEDs will work hotter so radiant loss will go up.

Oh, the number of hours is nothing to do with heat at all.

The change from 50,000 hours to 25,000 or 30,000 hours was based on EnergyStar/Lighting facts that only allowed X times the number of LED test hours to be on the package.

The change in the Philips slimline to 15,000 hours and 3 year warranty is that because the bulb is cheap, there is no marketing requirement for the customer to perceive it will last forever.

Semiman

 

[alpg88]

I just replaced a CFL bulb with an LED bulb. Holy crap does the base get hot. The glass bulb part only gets slightly warm but the base almost gets as hot as an incandecent. Hotter than the CFL. Makes me wonder how it can be so efficient...

i too noticed that, i bought 2 cree 100w equivalent bulbs in HD, i mesured heatsink temp, 93c. critical junction temp on xt-e is 150c.

 

[markr6]

i too noticed that, i bought 2 cree 100w equivalent bulbs in HD, i mesured heatsink temp, 93c. critical junction temp on xt-e is 150c.

I just returned one that died after about 15hrs. Not sure what caused it.

I really want to put some LED bulbs in fully-enclosed ceiling fixtures, but keep hesitating becasue of this.

 

[BLH]

I found a Cree precaution sheet on the HD web site for the 100 watt Cree bulb.
Said not for use in enclosed fixtures.
http://www.homedepot.com/catalog/pdfImages/71/719477ea-51d0-4d58-b513-79d8d443aa8a.pdf

 

[alpg88]

mine are not in enclosed fixture, they are pretty much open almost all around.

mine is a floor lamp just like this one, i even removed glass peice from the bottom of the "dish" for airflow

 

[hydro_pyro]

I use the 100w equivalent Feit/Utilitech "yellow ring" emitter LED's in 8" enclosed glass globes on my bedroom ceiling fans. So far, so good. I've left one running all day a few times by accident. No failures thus far...

 

[JohnnyGalaga]

So here's a question for the group. Most lamps have an annoying sticker on them that says something like "60w max power", meaning you're not supposed to use bulbs brighter than 60 watts. I've actually had a hard time finding floor lamps and table lamps that DON'T have this obnoxious safety limit. This 60 watt limit applies to the old incandescent bulbs.

So what happens now if we replace the 60 watt incandescents with CFLs or LEDs? What is a safe incandescent-equivalent wattage that I can use in lamps with CFLs or LEDs? If incandescents run hotter than CFLs and LEDs, then shouldn't it be safe to use something greater than 60 watt incandescent-equivalent?

I'm seeing CFLs at 1600 lumens that look tempting to buy, but I wanna make sure they won't get so hot as to exceed the lamp's 60-incandescent-watt limit.

 

[inetdog]

If your only concern is the rating of the fixture itself against damage or fire hazard, as long as you do not exceed the real power rating you should be OK.
The more serious problem (economically) is that the LEDs, fluorescent tubes and driver electronics will fail at a far lower temperature than the fixture itself. And just how and where to draw that line is an ongoing concern.

 

[JohnnyGalaga]

So the power rating (the 60-watt limit stickers) has more to do with, say, the safety / capability of the gauge of the AC wire and not the heat put out by the bulb?

CFLs are quite a bit cheaper than LEDs, and it would be nice to have 100-watt incandescent-equivalent lighting.

 

[SemiMan]

Not the wire gauge but wires and other pieces of the fixture, maximum temp transmitted to surrounding structure, etc from that incan bulb.

For the most part it does not apply to non incan.

 

[JohnnyGalaga]

Sounds like it's safe to get 100-watt CFLs or LEDs then? I just wish they weren't so expensive. And not having MERCURY, of all things, in a light bulb tends to be a plus. :huh:

 

[idleprocess]

So here's a question for the group. Most lamps have an annoying sticker on them that says something like "60w max power", meaning you're not supposed to use bulbs brighter than 60 watts. I've actually had a hard time finding floor lamps and table lamps that DON'T have this obnoxious safety limit. This 60 watt limit applies to the old incandescent bulbs.

So what happens now if we replace the 60 watt incandescents with CFLs or LEDs? What is a safe incandescent-equivalent wattage that I can use in lamps with CFLs or LEDs? If incandescents run hotter than CFLs and LEDs, then shouldn't it be safe to use something greater than 60 watt incandescent-equivalent?

I'm seeing CFLs at 1600 lumens that look tempting to buy, but I wanna make sure they won't get so hot as to exceed the lamp's 60-incandescent-watt limit.

Those are absolute electrical power ratings with the limitation being heat rather than luminous flux. Pretty much any edison socket CFL or LED you can buy today that will physically fit in there should be fine. 45 electrical watts is the most powerful CFL I've personally seen and it was physically enormous; I don't think LED is going much past 20W in the A19/A21 form-factor.

 

[slebans]

Those are absolute electrical power ratings with the limitation being heat rather than luminous flux. Pretty much any edison socket CFL or LED you can buy today that will physically fit in there should be fine. 45 electrical watts is the most powerful CFL I've personally seen and it was physically enormous; I don't think LED is going much past 20W in the A19/A21 form-factor.

If the circuit is on a dimmer then start-up inrush current along with peak repetitive current must be considered. Most of the manufacturers of bulbs or dimmers use a multiplying factor of 4 or 5. Effectively, in terms of the rated load of the dimmer - the LED bulb can appear as a load equal to 5 times the bulb's stated wattage.

http://www.lutron.com/TechnicalDocumentLibrary/367-2035_LED_white_paper.pdf


When controlling LED drivers, consideration must be taken to ensure the dimmer control is operated
within its rating (typically in watts, W). For example, the number of lamps able to be installed on a
single-phase control dimmer may seem like an easy question to answer; however, when using an LED
load, a 600W incandescent dimmer with a 15W LED lamp does not necessarily mean 40 lamps (600
divided by 15) can be used on this dimmer. While the LED lamp may only draw 15W continuously,
it may have a start-up inrush current or repetitive peak current during every half-cycle that makes it
appear much worse, i.e. act like a higher wattage load. That 15W LED lamp can cause the same
stresses on the dimmer as a 60W incandescent load. If you exceed 150W using 15W LED lamps, you
may overload the dimmer.

 

[idleprocess]

If the circuit is on a dimmer then start-up inrush current along with peak repetitive current must be considered. Most of the manufacturers of bulbs or dimmers use a multiplying factor of 4 or 5. Effectively, in terms of the rated load of the dimmer - the LED bulb can appear as a load equal to 5 times the bulb's stated wattage.

http://www.lutron.com/TechnicalDocumentLibrary/367-2035_LED_white_paper.pdf

This is clearly a key consideration when using a dimmer, but is independent of the question I was responding to re: fixture power ratings.

I personally never use dimmers so it's not even something that would cross my mind.