Timeline for Are LEDs in modern streetlights usually pulsed? If so, roughly what frequency?
Current License: CC BY-SA 3.0
13 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 14, 2017 at 12:37 | comment | added | Chris H | @uhoh It's more the definition of "few years". This was after the really big breakthroughs but before the Nobel. | |
| Jun 14, 2017 at 12:33 | comment | added | uhoh | @ChrisH one person's then is not necessarily the same as another person's then. My then is farther back than most people's then. I did some further reading in the last few hours and I can see that the more recent stuff looks just as you mention, a really broad plateau followed by a very gradual drop at much higher currents. There was a lot of work done over the decades; better crystal growth, then sapphire substrates, substrate lift-off too, then better MBE technology, plus better heat flow and solid-state modeling, etc. They don't give out Nobel Prizes for nothing you know. | |
| Jun 14, 2017 at 12:27 | comment | added | Chris H | @uhoh, the current at which the efficiency stops increasing is quite low. Efficiency is then almost flat before it falls off at least partially due to slef-heat (including heating from contact resistances). I went to a conference on this and other III-nitride matters a few years back: It was true then and it's more true now, that once you've got useful amounts of light coming out, driving them harder makes these LEDs less efficient. | |
| Jun 14, 2017 at 12:24 | comment | added | Janka | Does hrcak.srce.hr/file/125028 help you? Please note how it first says PWM dimming is a great solution if you don't want the color temperature change with luminance but then discards it completely in favor of an extensive discussion of DC/DC converters without any additional PWM on output? Because PWM is a feature of dimmable LED lighting, and a feature of lighting were color temperature is important. Both isn't the case for street lighting. | |
| Jun 14, 2017 at 12:07 | comment | added | uhoh | Can you add some link or supporting information? "LEDs used for street lighting usually employ a DC/DC converter of some kind" could very well be true, but I need something more than just saying so in order to accept. Thanks! | |
| Jun 14, 2017 at 9:08 | comment | added | uhoh | Real III-V MWQ LEDs are more than a little complicated inside, so arguments based on ideal diodes are helpful but incomplete. Let's find some data... | |
| Jun 14, 2017 at 8:40 | comment | added | Janka | Efficiency at low voltages is low because you cannot have light emmission if you don't jump over the band gap directly. But as soon you do, there is no sense in increasing the voltage any more — the overshoot energy is simply turned into heat. | |
| Jun 14, 2017 at 8:32 | comment | added | uhoh | I'll go do some reading and try to find some data. Starting from very low voltage (where there is heat generated and no light) and ramping up, the efficiency starts low, since it starts at zero. There is only non-radiative recombination. At you increase the voltage and the current increases, the ratio of radiative to non-radiative recombination improves, as do other aspects. I had thought that the plateau in efficiency occurred at a point beyond where heat could be removed for continuous operation, and so for the most watts of light per watt of electricity, it was better to add LEDs and pulse. | |
| Jun 14, 2017 at 8:27 | comment | added | Janka | Pulsing LEDs makes only sense when you want a high power output for a very short time with a LED not really designed to provide that power steadily. E.g. in an IR remote control. Over the glimpse of the thermal time constant (seconds), power needs to be balanced out to account for the heat dissipation. | |
| Jun 14, 2017 at 8:20 | comment | added | Janka | The circuit of most DC/DC converters has a coil on output, which —despite the pulsed nature of its working— automatically produces a more-or-less steady current. That's the very core function of such a DC/DC converter. | |
| Jun 14, 2017 at 8:18 | comment | added | Joren Vaes | I think he means DC/DC to not drive them directly from the AC line, instead turning it into DC and then pulsing that. | |
| Jun 14, 2017 at 7:56 | comment | added | uhoh | Are you saying that LEDs are driven most efficiently with DC, and not with pulsed current? Are the LEDs themselves converting electrical power to light with the highest power/power efficiency when the current is DC? Pulsed operation does not improve power/power efficiency for high power white light LEDs used in street lights? | |
| Jun 14, 2017 at 7:49 | history | answered | Janka | CC BY-SA 3.0 |