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

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

#11

Post by justinjlynn »

Hydraulix989 wrote: post #10
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…

I'd be shocked if the flicker went to 0% as this article seems to imply ("because LED flickering is even more pronounced, with the light dimming by 100% rather than the roughly 35% of fluorescent lamps") -- and I doubt the flicker for fluorescent lamps is at RMS. There's _gotta_ be at least a smoothing capacitor after the bridge rectifier (are they actually that cheap to omit one?!). I can't find a single LED driver…

Often the first things to be cut in cut-rate gear are comfort/longevity features such as smoothing capacitors and protection circuits. Generally if it doesn't have an effect on the return rate, it gets cut out to slash costs.

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

#12

Post by rhizome »

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…

the cheaper ones seem to have a blue/white tone whereas the expensive ones have a yellow/white tone and are warmer.

This is just normal color temperature and both come in all price points. I have several warm bulbs I got at Target on clearance for $2/2. I think it's just that the warm cheap LEDs are usually sold out, so all that's left are the prison-colored ones.

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

#13

Post by Zak »

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 both have the maximum score of 100. The average unspecified LED is in the 60s and sodium vapor lamps are negative. 90 is good for an LED, and 97 is the highest I've heard of someone testing in an LED[0].

CRI isn't the whole story on color quality, and it's possible to have high CRI with off tints or even a peaky spectrum outside of the specific colors the CRI standard tests, though the latter doesn't happen in practice. Several newer standards for measuring color quality exist, but are unlikely to be listed on a light bulb label.

[0] http://budgetlightforum.com/comment/1096106#comment-1096106

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

#14

Post by oasisbob »

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…

Agreed! It took several tries to get LEDs which worked well for vanity (i.e. Mirror) lighting. I thought it was a simple matter of color temperature - so wrong!

High CRI strip LED arrays are surprisingly hard to find. The end result was worth it though - skin looks natural, and the nearest commercial version is upwards of $800 - and I'm not entirely sure they got the CRI right.

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

#15

Post by cjsuk »

rhizome wrote: post #12
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…

the cheaper ones seem to have a blue/white tone whereas the expensive ones have a yellow/white tone and are warmer. This is just normal color temperature and both come in all price points. I have several warm bulbs I got at Target on clearance for $2/2. I think it's just that the warm cheap LEDs are usually sold out, so all that's left are the prison-colored ones.

It's not quite that. The cheap ones use white LEDs which are basically phosphor doped blue LEDs. They have a distinct blue peak which is far brighter than the overall output. The more expensive ones use blue LEDs with separate phosphor outside the LED chip. Philips do that. Seems to result in far better filtering of the blue part of the spectrum.

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

#16

Post by abainbridge »

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 distracting. For example, in a situation where you are pulling out of a T junction in the dark, you're less likely to see a motorbike when it is in the same part of your visual field as a car with flickering lights. Particularly when you are moving your head from left to right, as you do when at a T junction.

I'm not sure how to do the experiment though, since using TV screens, monitors or projectors wouldn't work.

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

#17

Post by torrent-of-ions »

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.

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

#18

Post by torrent-of-ions »

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…

By "100% clean" do you mean no flicker, ie. they use the more expensive components? I invested in Philips LED bulbs about a year ago and honestly I can't fault them at all. I consider myself to be sensitive to things like flickering. It doesn't usually give me a headache, but it will make me notice it to the point of distracting me. I was so happy to find that the Philips LEDs were almost just like old-fashioned bulbs (instant on, no flicker, warmer colour), but with virtually no heat output and vastly reduced power consumption.

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

#19

Post by KaiserPro »

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…

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.

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