When dimming tungsten lamps, it was pretty well known the efficiency dropped dramatically. In other words, you got less lumens (or whatever) per watt consumed. Does the same apply to LEDs? Or just to a lesser extent?
Dimmed using PWM or by varying the current?
LEDs are usually far more efficient than tungsten especially when dimmed but it does depend on the power supply design.
You probably get near the same efficiency from a PWM controlled LED as from one that is run at full current.
no, LED efficacy improves a bit when dimmed as V_f drops a little.
NT
A lot of these super bright leds seem to use pulse driven leds over running them in bursts to achieve the bright effect. I do not know how much this treatment shortens their lives, but according to some people on the web it has to be this way due to the poor thermal conduction of the led substrate. Not having ever seen a substrate I cannot possibly comment! Brian
Normally only true from the 80 to 100 % dimming range.
replying to Dave Plowman (News), tahrey wrote: The method by which they produce light is very much different from how tungsten filaments do, direct photon emission rather than having to make a piece of wire so hot it begins to glow, so I'd be surprised if their output light vs input power varies much from completely linear. Possibly they get a bit less efficient as you turn the brightness *up* (as the greater dissipated power, and greater current, makes for more heat that has to be sunk, which then doubles down by making the semiconductors less efficient), and the LED+Driver system as a whole may lose efficiency at low brightness depending on how the dimming is achieved (PWM switching, or simple inline resistance) and losses in switchmode transformers at marginal power draws (which is sort of analogous to the losses in a traditional dimmer switch itself, rather than the bulb).
The thing with the tungsten lamps is once you start reducing voltage below what they're rated for mainline use at, you're reducing their effective temperature and shifting their emitted spectrum further down the waveband; in other words, the ratio of light vs heat emitted switches more towards the heat end, and only avoids melting the filament because the total emitted power is so much less, thus less heat has to be dissipated even though it makes up a greater proportion of the total (similarly attempts to improve the efficiency and raise the colour temperature by increasing the voltage can only be taken a little way before the bulb fails, because although the proportion of power dissipated as heat is proportionally less, it's still materially more and ends up melting the filament).
So if you derate a 60w (consumption) incandescent bulb to 20w using a dimmer, it may go from producing 50w of heat and 10w of light (5:1, 16.7% efficient), to 17.5w of heat and 2.5w of light (7:1, 12.5% efficient; naturally these are not real world figures and just pulled out of the air). Your 12w LED replacement starts out emitting 2w of heat and 10w of light, derating to 4w in kind (ie 1/3rd) should see it emitting 0.67w of heat and 3.33w of light, and to emit the same brightness as the dimmed incandescent you'll instead want to derate to 3w (not counting transformer/etc losses), for 0.5w heat and 2.5w light.
The other clue is that the quality of light changes with incandescents when you dim them, the colour shifts towards the red-orange end of the spectrum (and beyond that, deeper into the infrared). The colour of a dimmed LED remains constant, with no wavelength shifts; it just reduces in quantity. So no additional heat should be produced, in fact due to the reducing current it should reduce in proportion to the useful output (ie visible light), and the losses will be traceable more to the power supply.
There are efficient ways to convert mains power to something LEDs can use, and cheap and easy/compact ways to do it, and there's not the greatest amount of overlap between them, so they should always be measured at the point of mains supply rather than at output to the diodes, but on the whole even the iffiest dimmable LED should remain more efficient than an equivalent incandescent... else you'll find an incandescent-like amount of heat being emitted from the electronics.
Which is one thing I dislike about LEDs. I tend to dim lights when I'm relaxing. And the 'sun going down' quality of the light from dimmed tungsten suits me well. And that's before LEDs not matching halogen quality when that's on full. Perhaps one day.
I've been saying similar for years, but the hue bulbs could be the answer but they arent very bright compared to anything else.
That could be the problem. The more you fiddle with LEDs to get a continuous spectrum, the more the efficiency drops. Same, really, as with florries - but more so.
I messed around with light transmitters when i was younger. a filament bulb could only have a very low amount of modulation added to it due to thermal lag. If you attempted to drive it anywhere near where you could see it flicker it sounded like a transistor radio with sand in the speaker. However early high brightness LEDs did not seem to have this problem at all. Obviously if you went to the almost off point it was clipped and you needed to watch overdriving for obvious reasons but none of that non linear effect otherwise.
Brian
When the blue leds came out merely by changing feedback in the drivers you could get the mixed light to dim a bit like a tungsten but I'd have thought all of that could be easily done nowadays in the actual driver chips.
After all I still imagine white is more than on Led in the same housing. I wonder if you could use a laser diode as a light transmitter? Brian
I don;t think that is true, blue LEDs needed a different 'chemical' in order to produce blue light nothing to do with driver feedback.
No, nothong to do with the driver.
Some use a specific LED for white light.
Well lasers do produce light not sure what yuo mean by transmitter though.
Its here now with the best of the LEDs which have full color temperature and dimming control and you are free to specify a set of color temps and brightness and switch between them.
who is trying to get continuous spectrum from LED lighting?
Halophosphates gave far closer to full spectrum than the more modern & far more efficient triphosphor coatings.
NT
Philips Warm Glow lamps dim spectacularly nicely even on standard dimmers and do shift red a bit.
Sadly, there's more to light quality than the nominal colour temperture.
Dips in the spectrum effect some colours but not others. Etc.
If you want colours to look fairly similar as in daylight, me.
True. But I reckon a decent triphosphor is closer than any LED I've come across.
Yes, but those more expensive leds go out of their way to do a lot more than just vary the nominal colour temperature.
Those don?t have dips in the spectrum for that reason.
so no-one commercially. For a long time researchers were trying to develop phosphors that only produced the peak light frequencies to improve efficacy.
90s CRI versus 80s. Moving away from continuous spectrum is more the focus of commercial research as it improves efficacy.NT
cobblers. Is this Rod again?
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.