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Our experiences with LED light bulb replacements
mouser:
Since we have some lightbulb experts here, perhaps this is a good opportunity for me to ask a couple of questions that i should have asked before i started my journey to LEDs.
I have (ceiling) light fixtures that state very clearly "MAX 60W [incandescent] BULB". So one of the motivations for me moving to LEDs is the ability to run brighter LED bulbs that give off lumens equivalent to a 100w incandescent.
But to be honest, I don't really know what that limit on the fixture is all about. I have had a circuit fuse throw once or twice that i attributed to overloading a light fixture with over-wattage bubls.
So I guess my question is -- what exactly are those max wattage limits on the fixtures all about? What is the danger of putting higher wattage bulbs in there? Am I right to assume that I can put BRIGHTER LEDs in there as long as the electricity drain is low? Am I right to assume that the LED bulbs will not generate dangerous heat levels?
Sarkand:
...However, I am motivated by the decrease in heat output -- in the summer my incandescents can generate a large amount of heat and i'm very keen to reduce that.
-mouser (May 16, 2014, 01:30 PM)
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I have installed three Kobi (made in China) LED 75W equiv., 5000K, in my room. One in a floor lamp, one in a table lamp and one in a reading/desk lamp. I have been very satisfied so far. I like the bright light - all three are essentially positioned for indirect lighting - but the desk lamp I have used for reading, and it's great.
I have noticed, however, that while the bulb itself stays quite cool (body temp?), the radiating fins at the base become quite hot. I am not able to touch them for longer than about .5 sec. at a time. Perhaps this is because of the "made in China" stigma deprecated above, but they have been working very well for several months with no problems. If what I have experienced is common, you really haven't done a whole lot to reduce total heat output. I'd like to know if others have detected this high heat of the radiating fins between the base and the bulb itself.
mouser:
The heat fins do get very hot.. Though that doesn't definitively tell us about heat comparisons.
My limited and shallow understanding of physics does tell me that since the LED bulbs are running so much more efficiently and using so much less energy -- that overall heat output must be significantly less, regardless of whether the fins burn your hand or not :)
But I could be wrong and I'd love to hear more from people who know. If I am wrong, then i have just poured a bunch of money down the drain for little good reason.
CWuestefeld:
Regarding the heat...
Light bulbs are hideously inefficient. Almost 100% of the input energy is converted to heat. And the improved bulb technology (tungsten incandescent -> CFL -> LED) is the result of improving on that efficiency.
But in any case, the amount of energy emitted by a lightbulb in the form of light is pretty tiny. Viewed another way, wiring up fifteen, hundred-watt incandescent bulbs is almost indistinguishable from a space heater. At the end of the day, the amount of heat you're going to generate is pretty much the wattage of the bulb, regardless of technology.
LED bulbs use far less watts, but still get hot. I believe that's because the LED is soaking its heat into a much smaller area. So an incandescent is making more heat and radiating it out through a relatively larger area. An LED makes less heat, by generating a similarly high temperature but radiating it out through a smaller area (so that if you touch a fingertip-sized area of each device, they feel about the same).
Sarkand:
The heat fins do get very hot.. Though that doesn't definitively tell us about heat comparisons.
My limited and shallow understanding of physics does tell me that since the LED bulbs are running so much more efficiently and using so much less energy -- that overall heat output must be significantly less, regardless of whether the fins burn your hand or not :)
But I could be wrong and I'd love to hear more from people who know. If I am wrong, then i have just poured a bunch of money down the drain for little good reason.
-mouser (May 20, 2014, 02:41 PM)
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I don't remember much of my high-school physics either, and I was mercifully spared in college. So I may be talking nonsense. But if I remember what little I do correctly, the total amount of heat generated by any electronic device is a function of its resistance, not the interplay of voltage, wattage and amperage. The efficiency of the bulb is due to reduction of wattage (don't know about the amperage, input voltage is obviously the same). But considerable heat can be generated at very low power, if resistance is high enough. Even a small flashlight bulb gets pretty hot when illuminated for a few minutes. Indeed, it's the heat produced by resistance that generates the incandescence. LEDs are more efficient because they use less total power throughput relative to incandescents to produce a roughly equivalent number of photons. This all seems pretty obvious. What is not obvious to me is why so much heat is still produced. Is the LED driver the equivalent of a step-down transformer? I think that would account for it.
I understand your desire to reduce heat - I have a similar problem in my place in the summer. I, too, thought they would run much cooler and was surprised to feel the high heat of the fins. But I wouldn't lament too much if you don't get the reduction you expected - if the bulbs perform as advertised, they will pay for themselves many times over. And surely someone has made this heat comparison somewhere. Have to see if I can dig it out.
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