LED Heat Generation

Flashlight Modding and DIY Parts
21

Is this where the 251lm/w comes from?
There is also a peak at 480mn (blue) that we are not consciously aware of that sets our circadian rhythm that is not reflected in that graph.

Other thoughts about this thread
I would assume CFLs are rated at full output, whatever that comes out to eventually
LED chips from Cree were rated at 25ºC, now many are the more ‘realistic’ 85ºC, but i assume you are correct pyro that finished bulbs are rated at a steady state output.
The 0.85 heat sounds like a rule of thumb, just like assume all energy is converted to heat (great rule to cover any situation the led will face), as output continues to increase at higher currents the rule won’t be applicable anymore (maybe a few years from now)

LEDs will always need heat sinksinking, being IC components they need to be kept from overheating and burning themselves out, but as the efficiency gets better less heatsinking will be required and hopefully eventually, only a little bit of it will be necessary per chip.

CFLs work at about 60-75 lm/w, any led below this is not worth it unless its in a form factor that CFL can’t duplicate (ie GU10)



I wish there was more information and more disclaimers on these two technologies on their packages and manufacturer’s websites.

CFLs burn out way faster when used in an on/off situation, they only have a fixed number of starts which is determined by how they were manufactured. This information is not available for any bulb i have looked into. I often use incandescent in bathrooms and other places where the bulb will be used only a few mins at a time as CFLs will only last a few months. LED replacements would be great if they were not as expensive as they are.

CFLS will last far longer then their rated hours if they are not switched on and off frequently. Any situation that has a light on 24 hours a day will make a CFL last double or more its rated life.

CFLs have a bad reputation because the market was flooded by super cheaply made junk, usually chinese manufactured

Neither CFLs or LEDs should be put in a closed fixture that doesn’t allow heat to escape, LEDs especially should be installed in a manner that allows maximum air flow for cooling, never in a closed fixture, and ideally in a fixture that has air flowing around it in all directions.

CFLs shouldn’t generally be installed outdoors unless in a closed fixture where the temp won’t get too cold

It seems low CRI in LEDS is to improve the lumens/watt, hence if we use XM-L to make bulbs they wouldn’t do well in the marketplace. As efficiency improves I hope to see single LED bulbs that put out over 1000 lumens per fixture under $10 each available at Home Depot.

22

The Sylvania 10W/500 lumen/PAR16/85 CRI bulbs that I have use 4 XML’s. Their original list price was $229 ea with Amazon selling them for around $105. You can get them now for under $40. There is still nothing else on the market that comes close to them in PAR16.

23

No, they’re not IC components. They’re diodes.

PPtk

24

That’s right they are,
But all the waste heat is generated at the junction of the diode, a very tiny area. This is a problem for high power LED’s. Other light technologies do not have to deal with the waste heat in such a concentrated area. An LED is a pinpoint light source AND a pinpoint heat source. Other light technologies inherently produce their light over a MUCH larger area and it’s waste heat also. Except for focusing applications, Flashlights, spotlights or directional lighting, LED’s have another inherent disadvantage. They produce highly directional light, which produce harsh shadows. I REALLY don’t see a future for a few high power LED’s in a fixture to emulate the kind of light we want in our homes or offices. That approach creates too much light and too much heat in too small of an area to be dealt with effectively. The future I see for casual LED lighting in the future, is arrays of relatively low power LED’s spread out over a larger area. This is actually the older tech that is now available and being used by many of the in home and office lighting. Perhaps some day, LED lighting will be able to be “printed” into large sheets, so that the light is evenly spread out over the entire area. Even now it is possible to buy cheap “strips” of led lights from FastTech for a very reasonable price. Here is the Link
About 1200 lumens for $10. Notice that the strip does not need ANY heat sinking. That’s because the light and heat is spread out over the 16 feet length of the strip, 300 led’s. Our own texaspyro used this type of light to great effect here: Replacing Lumiline light bulbs with LEDs

to simplify: for Flashlights, spotlights or directional lighting, high power led’s with massive heat sinking or active cooling. For in home or office, or anywhere where directional lighting is undesirable, large arrays or strips of many low power led’s. I really don’t see anyway around it, the physics will not allow it.

BTW, even older lighting technologies, Incandescent, florescent, etc. that already produce their light over a larger area, still rely on diffusers to try and emulate an even larger source of light. Look around your home or office, Incandescent bulbs are frosted (soft white), ceiling fixtures have frosted or white globes, even 4 foot florescent light fixtures will have diffusers or a reflector to spread the light out even further.

Go outside at noon on a clear sky, sunny day and you will see a sharp shadow of yourself and other objects. On a clear day, the sun is a point source of light in the sky and is focused (because its great distance) and casts sharp shadows. Then go out on an overcast day and you will not see any shadow. The entire hemisphere overhead is the diffused light from the sun, and appears to us as an “infinite plane” light source. An infinite place light source casts NO shadows, and it’s brightness does not vary with distance. THAT is the best source of light for every day living.

25

Very interesting, i found a datasheet on it, i should have mentioned T6 or U2 chips because of the low CRI, at 50 lumens/watt its less then CFL output, but in those small form factors CFLs won’t quite fit of course

26

True, but some manufacturers (bridgelux, sharp…) finally realized that and are now producing leds with double dome. Personally I could not believe when i fired up first bridgelux sm4 at 4W and could look directly in emitter without typical consequences. 8)

Led strips ? Sure but with some of these: http://www.sharpleds.com/doubledome.html and with proper “driving” not using resistors…

27

An often-quoted advantage of LEDs is that the LED’s light doesn’t produce heat, and is cool to the touch. LEDs are cool to the touch because they generally don’t produce heat in the form of infrared (IR) radiation (unless of course, they are IR LEDs)
Only 10% of the energy used by an incandescent bulb is converted to light; the other 90% is lost as heat.