LED light bulbs - temperature sensivity

[lavron]

Being disappointed with LED light bulbs that did not last a single month, I was looking for alternatives. I was surprised to find in the website

the following warning:

"important note concerning the installation of LED products:

"Excessive heat will cause LEDs to fail prematurely. "They must be operated in an ambient temperature,not exceeding room temperature, for maximum life time. "As the temperature rises above 23 degrees C, the life time goes down.

"Active cooling, such as a small fan, may be required if they are installed in a small enclosed space without ventilation."

Since summer weather temperatures go way above 23 degrees Celsius (73-74 degrees Farenheit) does this mean that LED light bulbs are useful only as refrigerator lights or in air conditioned rooms?

About two years ago I purchased from the C. Crane Company a LED light bulb indicated in their catalogue as item #20L. It contains 20 LEDs, produces light equivalent to at least 25W incandescent bulb, and is still functioning satisfactorily even though I did not take any precautions whatsoever to keep it cool. Unfortunately, this model has been discontinued, but the fact that the bulb survived summer temperatures suggests to me that the technology for manufacturing LED light bulbs tolerant to higher temperatures does exist.

I would appreciate it if someone here can recommend and provide references for vendors selling 120V LED light bulbs with standard household screw base connection, which produce light equivalent to 25W incandescent bulbs or brighter and which can tolerate summer temperatures.

[m Ransley]

For home use leds work but I stopped being interested in white Led when I saw lumen out put was apx 19 Lpw Lumen-per-watt, the same as incandesants. Flourescents go to 110 Lpw, unless better more efficient Leds are out now , why bother with them, plus they cost to much.

[Clive Mitchell]

In message , [e-mail] writes

I don't think this has anything to do with temperature at all since LED lamps tend to run almost cold due to their very simple capacitive power supply and low output. It's most likely that the problem that prompted that company to put the warning up was just crap quality white LEDs being used in their products. The first white LEDs from China had a terrible failure rate due to the fact the technology was basically copied badly and manufactured sloppily.

When their lamps started failing they probably made the assumption that it was for the same reason that compact fluorescent lamps fail, and blamed temperature.

As the Chinese get better at making white LEDs this should change for the better.

I'm afraid it's down to trial and error. Even the best sources can get a bad batch of LEDs, so even two lamps of the same style and brand could have a different performance.

Another thing that fries LED lamps is people operating the 12v units on electronic transformers which put out a much higher peak voltage due to their pulsed operation.

[Don Klipstein]

My experience has been different. I notice temperature rise of the lamp housing surface above the ambient, temperature rise of the air in the lamp above that of the lamp housing surface, temperature rise of the leads and surfaces of the LEDs above that of the air in the lamp, and typically the LEDs have current on the high side - meaning a higher figure for temperature rise of the LED chips above that of the LED surfaces. At 20 mA, a usual 5 mm white LED has its junction temperature around 18 C above that of its leads (as measured 5 mm from the LED body).

I do agree that this can also be a factor.

- Don Klipstein ( [e-mail])

[lavron]

Two points.

1. If I understand the warning correctly, it applies to environmental temperature, as well as temperature rise due to heat generated by the bulb.

1. I agree with you that the LED bulbs SHOULD NOT generate sufficient heat to explain significant temperature rise, but one still active from the batch that contains the failed bulbs warms up enough to be felt by touch of the glass bulb.

I am using the 120V LED bulb to light my computer keyboard. Since the bulb is fed by the UPS, I prefer the LED bulb in order to reduce the load on the UPS during power failure. Since I did notice a voltage peak in the UPS when it turns on, I wait for it to stabilize before turning anything else on, including the light. Still, two bulbs did not survive a month each. I believe this is due to poor workmanship. Trial and error at the prices of these bulbs is not good enough. I am hoping for someone to report good experience with some brand and/or vendor.

[w_tom]

Its a well established trend. As LED wattage increases, the efficiency drops. LEDs are slowly moving up the incandescent light product line as LED efficiency at higher wattage gets better. Currently, LEDs have not yet conquered the tens of watts market. However some of those incandescent lamps are replaced by LEDs when the LED's ten year plus reliability is required. And yes, those high wattage LEDs also require well designed heatsinks.

In earlier days - especially after that L-1011 crashed into the Everglades - then LEDs replaced 327 incandescent bulbs. Early LEDs to replace 327s cost maybe $100. As technology advances, the price drops and LEDs get more efficient at higher wattages. But currently the LED is not yet there to replace an incandescent room light.

It is a well establish principle of consumer electronics. The new product must provide a decade of improvement. Low wattage LEDs accomplish that. High power LEDs currently do not. Meanwhile a technology that originally predated Edison's light bulb - fluorescent - does provide that necessary advantage.

Another source of LEDs to replace any > Two points.

[Victor Roberts]

I agree that the heat rise above ambient of 20ma LEDs is minimal, but your blanket statement certainly does not apply to high power LEDs such as any of the Luxeons. These will all overheat if not connected to a proper heat sink.

As for the impact of ambient temperature on LED life, there is published data from the LRC that clearly shows decreased life for even small LEDs when they are operated in a high ambient temperature. Data for low power LEDs was presented at the 2002 IESNA Annual conference but I can't find the paper any more on the LRC Web site. Here is the full reference.

Narendran, N., and L. Deng. 2002. Performance characteristics of light-emitting diodes. IESNA Annual Conference. Technical Papers 157-64. New York, NY: Illuminating Engineering Society of North America.

LRC data for high power LEDs can be found at:

[Fritz Schlunder]

Ah hah! There is a fairly high probability the cause of your LED bulb failure is not due to any inherent manufacturing flaws or low quality workmanship or anything of the like really. The problem is most likely an incompatibility between your specific LED bulbs and UPS power source.

Typical LED bulbs designed for operation from 120V AC often use a capacitive ballast (with a small inrush limiting resistor) to limit the current through the LEDs. This is a very cheap, efficient, and easy to implement solution, so it is very commonly done.

The problem is, a capacitive ballast must be operated with a truly sinusoidal power source (like the mains are). The current through a capacitor is I=C*dV/dt where I is current in amps, C is capacitance in farads, and dV/dt is the time rate of change of voltage per unit time in volts per second. A clean sinusoid has a very slow maximum rate of change of voltage, so the peak current that the LEDs normally are subjected to is fairly low. In other words, the current crest factor of the capacitive ballast when powered from a sinusoidal source is fairly modest.

Your UPS most likely does not produce anything at all like a clean sinusoid (especially when powered by battery, although depending upon it's design it may never produce clean sinusoids even when the AC mains are fully energized). If you look at the output on an oscilloscope you may find that it is rather a square wave output that goes between 0V (with significant dwell time), 150V, 0V, and to -150V or something like that. Or it could be some kind of stepped square wave that more closely approximates a sine wave, but is still very much not a sine wave since it has high dV/dt edges, or at least steps. These high dV/dt edges will cause very high peak currents through the capacitive LED ballast, and the current crest factor will be outrageously high, likely much higher than the LEDs are specified to be able to handle reliably. Hence your LED lamp failed in very short order.

Had the LED lamp been operated from a truly sinusoidal power supply, they would likely have been much more reliable, quite possibly meeting the claimed life expectancy ratings.

[Noozer]

And this is most likely your problem.

A UPS puts out a very dirty signal that will easily destroy the cheap electronics within the LED bulb. If you can find a oscilliscope reading of a normal outlet and one of an average UPS I bet you'd be surprised by the difference.

[lavron]

I greatly appreciate your detailed explanation, as well as Noozer's, for the reason of my problem. However, I need a solution. I do not need LED light bulbs for general lighting, since I prefer the compact fluorescent bulbs for this purpose. I need LED light to illuminate my keyboard because of its very low power consumption. Its being directional is also a boon.

Noozer points out that the electronic components within the LED bulb are cheap, implying that with better quality electronic components the bulb might last longer. Would it be possible to place between the UPS and the bulb a filter, made of quality components, that would smooth down those sharp edges? If so, where can I find a good design for such a filter and specifications for its components? I am willing to consider building one myself.

[Adam Aglionby]

Simple answer would appear to be to modify a desk lamp with LEDs and take 12V power from the computer PSU.Disadvantage of light shutting down with computer. Or hack the UPS to obtain low voltage D.C. source from internal batteries.

Adam

[Daniel J. Stern]

Eh? Come again? How does the plane crash relate to the LED retrofitment?

[Michael Daly]

Given the money spent so far, just get a powerful flashlight and use lithium batteries to power it. They have shelf lives of about a decade and can provide power for quite a while.

If power failures are so frequent that this is too expensive, get a backup system that uses a better quality inverter - check with the companies that sell off-grid power systems.

Mike

[Rusty]

Even easier would be to get a keyboard that is rear illuminated, but those are sometimes pretty cheaply made or horribly expensive.

Also, you could get a USB powered LED light, or make your own (Clive's site has some ideas;)

[Clive Mitchell]

In message , [e-mail] writes

I wouldn't actually recommend using the lamp on a UPS, especially a consumer level unit. Their output isn't necessarily going to be the smooth constant voltage sinewave that the lamp is designed to work with.

[Clive Mitchell]

In message , Daniel J. Stern writes

The lamp in the toilet blew, and when the pilot went to find a torch the plane crashed.

Probably.

(I'm guessing it was probably a runway light that failed.)

[Clive Mitchell]

In message , [e-mail] writes

Just plug your LED lamp in before the UPS and keep a torch handy for if the power goes down.

[Clive Mitchell]

In message , Adam Aglionby writes

Or use the handy 5V supply from any USB port to power a small cluster of LEDs?

[Clive Mitchell]

In message , Victor Roberts writes

Most LED lamps use clusters of 5mm LEDs. There are a few Luxeon versions, but I shudder to think what the circuitry is like inside them.

If it's the early Chinese white LEDs, then even using them in a fridge wouldn't make them last longer. :)

[Noozer]

Why does this need to be plugged into the UPS at all? If you need light in case of a power outage GET A FLASHLIGHT!