Think it's generally known that dimming a tungsten bulb reduced its efficiency dramatically. In other words, a 100w dimmed to half brightness used a lot more electricity than a 50w on full. Although dimming did extend the life of the bulb.
So how about LEDs? Since they generate far less heat are they still as efficient when dimmed? And does dimming make a difference to their life?
In the early days of pocket calculators, the red LEDs they used were pulsed in order to extend the battery life, so I can guess from that much alone what the answer is.
That was generally a consequence to reducing the Chip IO to drive the LEDs in a matrix scheme with column and row multiplexing.
Many LEDs lose efficiency at high currents. This is one discussion on the effects:
"The Inconsistency of Dimmers with LED Lamps" Doug Lindsey, Electric Power Research Institute Frank Sharp, Electric Power Research Institute Teren Abear, Southern California Edison
It stands to reason, there's a reduction in bulb temperature at low settings, which would have some impact on SMPS life.
For the LEDs, the model is less clear. The paper itself isn't worth much, except it throws shade on using plain Arrhenius modeling and accelerated life testing. We could probably say that Arrhenius isn't dead, and a cooler LED last longer. But real life is apparently not as nice as theory.
With PWM control, the current is delivered in constant amplitude pulses (this prevents colour shift), but the temperature will drop due to the reduction in average power.
It doesn't do much to explain how the first generation of bulbs promised 25000 hours and now there are some 10000 hour bulbs. Shades of past cartels ? :-) Well, everything is engineered within an inch of death, so why should a lowly LED lightbulb be spared such treatments ? If my car real axle only has 10% margin, when 70 years ago there was 300% load margin, who is the wiser ? No one will ever know. Some old timers will look under a car and marvel at the spindly axle used. A car executive had a larger steak dinner tonight because of that, making the choice well worth it.
Until they can make the colour temperature of LEDs drop as they dim, I?ve decided I?m going to just avoid using dimmers with LEDs as the just look ghastly as the dim IMO.
Tim
At a guess, if they stay as warm, pretty much, although light as a proportion of heat is less. If the fitting gets cooler as you dim, then I'd say yes, the efficiency is fairly linear.
Plenty of lamps now use both cold and warm LEDs, and can smoothly change colour temperature (e.g the ikea ones between 2200 and 4000K)
Controlling those from a "hub" I can have a wake-up routine that fades up the brightness and colour temperature together.
I'd be surprised if someone doesn't make a lamp that does the same by itself...
Some do IME. I used some of these:
The life of the dropper circuitry in the lamp will be extended by lower temperatures, and possibly the life of the LEDs themselves by being run less "hard". However its often the former that kills the lamp rather than the latter.
Thanks. What?s the key search term to make sure I get the right ones? I could do with some candle bulbs with standard bayonet fittings.
Tim
Tim+ explained on 28/04/2021 :
I only have two on dimmers, all the way from full on to out. The colour remains the same irrespective of brightness setting, but I don't have any issue with that at all. Contrast that with tungsten, which becomes more yellow/red as it is dimmed.
Any effect is small compared to incandescent where it's huge, and it depends how hard you're driving the LEDs in the first place.
Philips has produced some mains LEDs which are claimed to be more efficient and longer lasting mostly by increasing the number of LED chip and running them at a lower power per chip. Obviously this costs more.
Not sure if there is a key search term, I just know that that particular one I linked to behaves in that way. There is a reasonable chance that other lamps in the same range may behave like that.
I was forced into going LED in the kitchen. The design of tungsten lamp being NLA. Basically a 100mm globe lamp in a shade above the table, which I liked the look of. Did find an expensive LED which looks much the same, but that also required a new dimmer (one of 3) so decided to replace the other two tungsten circuits which light the worktops via downlighters with LED too. And they were PAR 25, and difficult to find LEDS for them too, but eventually did. Total cost about £150. I've now got used to the colour temperature staying the same when dimmed and don't mind it. As I already had dimming florries as under cupboard lighting, and they keep the same colour temp when dimmed.
I had a rather odd-ball CFL with internal dimmer, it went a pinkish colour when dimmed very low.
Enter the fitting name plus "2200-2700K" to catch the adjusted mixing. Throw in a "dimming" or "dimmable".
The "2200-2700K" is what stood out in the available data. A regular bulb won't be stated that way.
Paul
Yes, I think originally incandescent lamps (tungsten I assume) had a lifespan of about 2500 hours, but (in 1925) they reduced it to 1000.
In the 1970s they started selling "double life" lamps that lasted 2000 hours (at a slight reduction in efficiency as they operated at a lower temperature), but they never caught on as the standard ones were heavily discounted, presumably due to volume production.
Which is exactly the effect I want when I dim a light. It creates a ?warmer? or ?cosier? atmosphere. Straight dimming of an ordinary LED just make a room look cold and dingy.
Tim
Increase it a bit I would have thought. Of course you've got to dim it using PWM (from DC) or trailing edge (AC).
(I've seen idiot YouTube videos describing circuits that control LEDs with potentiometers, either directly or via a power transistor; it's inefficient and liable to overheat the pot and/or the transistor as some of the comments say; also I think that controlling white LEDs in this way is liable to change the colour of the light.)
Idiot YouTubes:
Thanks again. I found the bayonet version that I wanted and was about to order 5 for a ceiling light in our sitting room but then remembered that we only ever turn the light on when we first enter the room. After that we use a desk & standard lamp (both LED) with another standard lamp if we need more light.
I reckoned in terms of ROI I?d probably have to live to 150 to make swapping all the bulbs worthwhile. ;-)
Still, nice to know such bulbs exist and who makes them for future reference as I?ve got some G9 fittings that need replacing in our dining room and I would like a dimmable overhead light here.
Tim
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.