Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The scientific reason you don’t like LED bulbs – and the simple way to fix them

theconversation.com

Post reply on HN
Print view View original

41–50 of 70 posts

Re: The scientific reason you don’t like LED bulbs – and the simple way to fix them

#41

Post by eternauta3k »

mollusk wrote: post #33
KaiserPro wrote: post #19

Earlier quoted context omitted.

I suspect its not the PSU, its the PWM for the dimming. compared to actually lowering the voltage/current of a LED/light/other its far simpler and cheaper just to turn it off and on again at varying duty cycles/ frequency.

Correct me if I'm wrong, but isn't it just the de facto way of dimming LEDs? Since as opposed to incandescent bulbs, they require certain voltage/current to be lit, if you pass them less, they simply won't emit light.

You can feed it DC and vary the current, for example by filtering the pwm.

Re: The scientific reason you don’t like LED bulbs – and the simple way to fix them

#42

Post by Shivetya »

torrent-of-ions wrote: post #17
abainbridge wrote: post #16

What gets me are side-lights on cars that flicker. Cars have DC electric systems in the first place. Where did the Audi engineers find 100 Hz to run the LEDs from? I guess there's a switch mode power supply to convert down from 12 V to something lower that the LEDs need. But AFAIK, switch mode power supplies don't switch at 100 Hz. I'm pretty sure you could show by experiment that flickering car side-lights are distr…

That is seriously annoying. Not only do they flicker, they are slightly blue as well. I have mistaken an Audi for an emergency vehicle in my rear view mirror on multiple occasions. I am sure that this is their plan. Such lights should be outlawed.

Now I have found that some mirrors on cars and even motorcycles can distort the reflected light to give blue points. combine with polarizing glasses and it becomes even more difficult to find the exact cause.

now if viewing straight on without another element to distort the light, like polarized lenses; I would be interested if the reflector built into the headlamp assembly can cause an issue.

Re: The scientific reason you don’t like LED bulbs – and the simple way to fix them

#44

Post by dreamlayers »

abainbridge wrote: post #16

What gets me are side-lights on cars that flicker. Cars have DC electric systems in the first place. Where did the Audi engineers find 100 Hz to run the LEDs from? I guess there's a switch mode power supply to convert down from 12 V to something lower that the LEDs need. But AFAIK, switch mode power supplies don't switch at 100 Hz. I'm pretty sure you could show by experiment that flickering car side-lights are distr…

Many rear car LED lights flicker because their full brightness is used as brake lights, and they are dimmed via pulse width modulation for normal lighting. This is simply a bit cheaper, which is ridiculous on an expensive car.

I don't actually see the flicker normally, but when they quickly move accross my visual field I sometimes see a line of dots from the flicker.

Re: The scientific reason you don’t like LED bulbs – and the simple way to fix them

#45

Post by dreamlayers »

Zak wrote: post #13
cjsuk wrote: post #8

I've had this problem and decided to test the problem away. Used a Vishay visible spectrum phototransistor and my scope. Think it was a BPV11 transistor. Philips bulbs are 100% clean. Poundland ones are not. Cheap no brand ones from Amazon are not. The latter two have a 100Hz output. I suspect the hatred for LED bulbs stems from the cheap ones which use the lowest cost solution to get mains voltage into a constant cu…

Another issue is that many LEDs have peaky spectra. This makes cool white harsh and warm white dingy. This isn't limited to cheap products, as producing a fuller spectrum with LEDs is less efficient. I'll take the efficiency hit for better light; the most common measure used, printed on the packaging of some bulbs is CRI (color rendering index). It's based on blackbody radiation, so incandescent bulbs and sunlight bo…

Yeah. The best example was lighting all my clothes with LED lights. Colours seem obviously messed up. Some colours are emphasized while others are suppressed.

Re: The scientific reason you don’t like LED bulbs – and the simple way to fix them

#46

Post by jonsen »

Say you have an LED which can sustain 1 Watt of continuous power. If you feed it 10 Watt in fast pulses with a pulse/pause ratio of 1:9 it would still be 1 Watt on average, but the light intensity impression to the human eye would be higher.

Re: The scientific reason you don’t like LED bulbs – and the simple way to fix them

#47

Post by SmellyGeekBoy »

cjsuk wrote: post #8

I've had this problem and decided to test the problem away. Used a Vishay visible spectrum phototransistor and my scope. Think it was a BPV11 transistor. Philips bulbs are 100% clean. Poundland ones are not. Cheap no brand ones from Amazon are not. The latter two have a 100Hz output. I suspect the hatred for LED bulbs stems from the cheap ones which use the lowest cost solution to get mains voltage into a constant cu…

Thanks for sharing, especially as it confirms my suspicions!

A few years back we changed every single bulb in our house (including the GU10s in the kitchen) to Philips CorePro LEDs. I've never seen this "flicker" or had any complaints about it from visitors (nobody even seems to notice that anything is different until I point it out). I also recently fitted out an office with SkyTile LED panels. Again, no flicker.

When I'm in a house or an office with cheaper LEDs for more than a few hours I find it very straining on my eyes. Then again, I had the same issue with CFLs, which is why I made the decision to change everything to LED in the first place.

Re: The scientific reason you don’t like LED bulbs – and the simple way to fix them

#48

Post by cjsuk »

SmellyGeekBoy wrote: post #47
cjsuk wrote: post #8

I've had this problem and decided to test the problem away. Used a Vishay visible spectrum phototransistor and my scope. Think it was a BPV11 transistor. Philips bulbs are 100% clean. Poundland ones are not. Cheap no brand ones from Amazon are not. The latter two have a 100Hz output. I suspect the hatred for LED bulbs stems from the cheap ones which use the lowest cost solution to get mains voltage into a constant cu…

Thanks for sharing, especially as it confirms my suspicions! A few years back we changed every single bulb in our house (including the GU10s in the kitchen) to Philips CorePro LEDs. I've never seen this "flicker" or had any complaints about it from visitors (nobody even seems to notice that anything is different until I point it out). I also recently fitted out an office with SkyTile LED panels. Again, no flicker. Wh…

Yeah it's the CorePro or Master ones I used. Recent ones have been these units: http://uk.rs-online.com/web/p/products/1244319/

CFLs are awful. I got rid of all of mine years ago back when LED bulbs were £20 a piece. Was worth it even at that cost!

Re: The scientific reason you don’t like LED bulbs – and the simple way to fix them

#49

Post by Johnny_Brahms »

lucaspiller wrote: post #21
cjsuk wrote: post #8

I've had this problem and decided to test the problem away. Used a Vishay visible spectrum phototransistor and my scope. Think it was a BPV11 transistor. Philips bulbs are 100% clean. Poundland ones are not. Cheap no brand ones from Amazon are not. The latter two have a 100Hz output. I suspect the hatred for LED bulbs stems from the cheap ones which use the lowest cost solution to get mains voltage into a constant cu…

It's not just cheap LEDs unfortunately. I bought some expensive recessed lights with Osram drivers (~€80/light), and even those flicker a little.

I have a different experience. Osrams dont flicker (measured using the cheapo way: deferent types of cameras), whereas Philips LEDs do.

But otoh the osram ones have all failed or started blinking due to what I think is over heating.

Re: The scientific reason you don’t like LED bulbs – and the simple way to fix them

#50

Post by gargravarr »

I find this a problem with my LED-backlit LG monitor. It's ridiculously (by which I mean, blindingly) bright at full brightness, but anything below and the imperceptible flicker gives me migraines. So I have the choice of impossible brightness with no flicker, or acceptable brightness with headaches.

I don't get why LED bulbs need to flicker though - the bulbs don't dim, and if they're providing steady light, they should be operating permanently. If it's a heat production problem, the bulbs need heatsinks, not PWM.

I've found a vast array of modern tech to be completely unusable for me because of this. I can stare at the CCFL-backlit screens on my workstation all day, but a few minutes of my home monitor is enough to send me straight to bed in darkness.

Post reply on HN