Beware of LED bulb flicker? - Page 1
Forum section: electronics / general

author: Tom45
author_rank: Frequent Contributor
timestamp: July 29, 2017, 06:37:11 pm
content: http://www.dailymail.co.uk/health/article-4739766/Low-energy-LED-lightbulbs-giving-HEADACHES.htmlAnother thing to worry about?"Professor Arnold Wilkins, professor of psychology at the University of Essex"says"While fluorescent lights, such as those in offices, dim by around 35 per cent with every flicker, LED lights dim by 100 per cent."That is the first I heard about this "problem". And I haven't noticed the flicker myself.So I measured a couple of different LED bulbs, both 100 watt "equivalent".The flicker is there (120 Hz), but only about 5%, not 100%. Using a photodiode the level was about 300mv with 15mv p-p ripple on top of it.Are there LED bulbs that really do go between 100% and 0%?

author: kalel
author_rank: Frequent Contributor
timestamp: July 29, 2017, 06:39:28 pm
content: Quote from: Tom45 on July 29, 2017, 06:37:11 pmWith a Joule Thief circuit and a small self color changing RGB LED, I noticed that it stays at the first color constantly (without a capacitor added). Now, I don't know if it needs to drop to 0 for that to happen. But Joule Thief (without or even with a capacitor) is not the standard power supply case.

author: MK14
author_rank: Super Contributor
timestamp: July 29, 2017, 06:53:20 pm
content: Quote from: Tom45 on July 29, 2017, 06:37:11 pmI think (based on what BigCliveDotCom's youtube video says, so I could easily be wrong).But supposedly, the newer LED bulbs or lighting, may start to have NO capacitors in them (new designs, probably to reduce production costs). These therefore, may well have 100% on/off, flicker (or whatever you want to call it).But they maybe only for outdoor use, I'm not sure.tl;drNew one piece LED "chips", without much/any capacitance, to hold the LEDs on, during the off (low voltage) parts of the AC mains cycle.N.B. I could easily be wrong. I only have weak information about it at the moment.tl;dr2What I mean is that the old/existing LED lamps have controllers as well as the LEDs. The newer type, ONLY has the LEDs, the controller is built into the LEDs (chip on board, COB), but hence has little/no capacitance. Hence the 100% on/off flicker situation.tl;dr3Hopefully only a minority of future LED bulbs will be the high flicker type. So that if you buy decent bulbs at reasonable prices, they will have minimal/reasonable flicker.

author: georges80
author_rank: Frequent Contributor
timestamp: July 29, 2017, 07:05:02 pm
content: Quote from: Tom45 on July 29, 2017, 06:37:11 pmAh, professor of psychology, yep, and reported in a newspaper, check, must be true (hard) scienceMaybe with a LED wired directly across AC, but any decent 'bulb' has an electronic ballast (high frequency switcher) and will compensate for most the AC cycle by keeping the LEDs fully driven. Then add in the caps used in the ballast and then factor in that the LED phosphor takes quite a few milliseconds to go off completely.So, the 100% off would be quite an engineering challenge to achieve (with white LEDs).There's a heck of a lot MORE flicker with non-electronic ballast fluoros.Simple flicker test is to quickly move (back and forth) your open hand with fingers spread between your eyes and a LED/Fluoro etc light source - easy to see any strobe effect if the flicker is large magnitude.cheers,george.

author: MK14
author_rank: Super Contributor
timestamp: July 29, 2017, 07:16:40 pm
content: In this one, he shows it with and without the capacitor. I.e. one flickers and the other doesn't flicker much.Unfortunately, the one he reviews is suppose to NOT have the anti-flicker capacitor.

author: Tom45
author_rank: Frequent Contributor
timestamp: July 29, 2017, 07:25:38 pm
content: Quote from: MK14 on July 29, 2017, 06:53:20 pmInteresting video tear down.Lets hope that this design with no capacitor doesn't become widespread.

author: MK14
author_rank: Super Contributor
timestamp: July 29, 2017, 07:34:50 pm
content: Quote from: Tom45 on July 29, 2017, 07:25:38 pmIt probably costs relatively little to add the capacitor (but it could be expensive, bigger capacitors at higher voltages, can be expensive), and get a nice, relatively non-flickering LED bulb/lighting. Even if it does cost a fair bit. It is probably well worth the money.But in practice, I fear that many people, will try and buy the cheapest possible LED bulbs that they can.E.g. buy them at a $1 store, or because it is $1.99 each, somewhere.Therefore, if they produce these really cheap, capacitor free, LED lamps. Also because many people CAN'T see or perceive the flicker. They will sell in HUGE quantities.Basically, my experience of people, is that they will try and buy the cheapest possible LED bulbs they can. I can try explaining to people that spending more, can actually be cheaper because they may last longer, be more reliable and give better quality light (e.g. colour temperature).But I suspect they will still go out and buy the cheapest, LED bulbs, available for sale.

author: IanB
author_rank: Super Contributor
timestamp: July 29, 2017, 08:02:41 pm
content: White, high brightness LEDs use a phosphor that is excited by blue/UV light, similar to fluorescent tubes. So the extent of the flicker will also depend on the persistence of the phosphor as well as the drive circuit. There is a gap of between 4-5 ms between the peak of the AC cycle and the next zero crossing. Will the phosphor lose all light emission during that interval? I do not know.

author: MarkS
author_rank: Unknown
timestamp: July 29, 2017, 08:15:34 pm
content: Something tells me he read about PWM being used to dim LEDs and made the leap.

author: georges80
author_rank: Frequent Contributor
timestamp: July 29, 2017, 08:19:59 pm
content: Quote from: IanB on July 29, 2017, 08:02:41 pmLike I wrote above. Yes, the phosphor helps a lot. Any DECENT bulb has an electronic ballast. The LEDs won't turn off just because the AC has come off the 'peak'. There's only a significantly shorter period of time where the voltage is lower than the LED + ballast operating voltage.I purchase only Cree bulbs - the CRI (of the warm whites) is fantastic and I haven't had a failure yet and a few are on at least 6 hours per day every day and are at least 4 yrs old. Spend once and get something decent or buy $1 garbage - consumer choice.The video above shows one of the cheap panel LEDs (typical of chinese flood lights etc), you get what you pay for in terms of ballast design (or none...).Of course a cheap implementation will have even worse visible flicker at 50Hz vs 60Hz.cheers,george.

author: Someone
author_rank: Super Contributor
timestamp: July 30, 2017, 12:29:00 am
content: Quote from: IanB on July 29, 2017, 08:02:41 pmThe phosphors used on white LEDs unlike the historical ones used in CRTs have extremely short time constants in the sub ms to us region, anything shorter is blurred by the slow speed of the exciting LED. Recall that white LEDs are used as flashes for phone cameras (although they tend to be specialty parts).

author: Buriedcode
author_rank: Super Contributor
timestamp: July 30, 2017, 12:37:02 am
content: Well, the 'Daily Mail' is probably the worst paper for scare-mongering and pseudo-science in the UK (every day warns that something causes cancer, whilst something natural cures it, and generally just tries to blame everyone's ails on some trendy scapegoat subject like wind farms, "chemicals" or political correctness).Also, psychologists have a way of coming up with theories and studies that can't be replicated, as such, more than any other science, its findings and theories should be taken with a huge pinch of saltWith that said, I do believe flickering lights can cause headaches - lots of things can cause headaches, especially lighting. (examples include, diet, posture, gait, asking someone if they have a headache - a good proportion will have a headache when you ask them).As to whether its all LED bulbs (unlikely), how noticeable the flicker is, how many will be negatively affected, its anyone's guess. Whilst I'm sure there will be some LED bulbs sold that will have noticeable flicker - it seems to be the source (the daily fail) is implying its ALL LED bulbs.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 30, 2017, 02:41:47 am
content: A lot of LED backlit TVs intentionally strobe at 120Hz or higher to reduce motion blur. Basically, if the LCD transitions only while the backlight is off, the user doesn't see it. The result is a display more like a CRT or plasma.https://www.blurbusters.com/zero-motion-blur/lightboost/Where 75Hz and greater flicker can cause headaches is if you're trying to film stuff.

author: Chalcogenide
author_rank: Regular Contributor
timestamp: July 30, 2017, 07:32:11 am
content: A type of LED bulb that for my experience is very bad in terms of flicker is the one with the so-called "LED filaments". The LEDs are in series, thus requiring high-ish voltage (90V per filament or so), and manufacturers often save money by using a capacitive dropper supply with very little filtering capacitance, or none at all. I bought few of them to use in the living room but I could "feel" that something was wrong. When I checked for flicker, they were essentially off for half of the time... I had to move them to a room where I didn't spend as much time in, and replace them with "normal" LED bulbs.

author: Kjelt
author_rank: Super Contributor
timestamp: July 30, 2017, 08:19:08 am
content: It might be very personal, some persons are very susceptible to these things but will soon notice it.For instance with single DLP projection systems where there is a colorwheel and the colors are projected in very high frequency one after the other about 10% of the people have the rainbow syndrome where their visionary system is able to see the different colours instead of the total picture causing headaches and nausia.Now for the led lighting, probably with cheaper ledlighting where no fancy driver is used for cost down this might cause problems for some people, i would not be surprised.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 30, 2017, 09:07:11 am
content: They could reduce the flickering a lot by combining one such led chain with current limiting and one with a capacitive dropper. Still the large capacitor needed (more like 5-10 µF range, like the motor caps) could be a cost factor. For a first test one could use 2 of such modules, one with a capacitor in series.With large installation of old style florescent lamps they used this to improve the power factor and reduce the flicker.

author: madires
author_rank: Super Contributor
timestamp: July 30, 2017, 11:33:05 am
content: AFAIK the series cap in old fluorescent lamps is just for compensating the phase shift by the ballast. Our electricity providers demanded that for large installations of fluorescent lamps. Today's fluorescent lamps got electronic ballasts with a proper power factor.

author: Vtile
author_rank: Super Contributor
timestamp: July 30, 2017, 11:54:51 am
content: I'm not commenting in other parts of this than that the flicker of the light source is studied phenomenom. In fluerescent lights mainly in office and school environments which is lightly connected eye distress and that sort of thing. This from memory and this is not my area of interest, but I just to want to point out that the flicker is studied even before led became mainstream.

author: tooki
author_rank: Super Contributor
timestamp: July 30, 2017, 12:03:55 pm
content: Yep. With LEDs, it's just more pronounced because of their essentially instantaneous response time (compared to the low pass filter effect of a heated filament or slow phosphors in fluorescent lamps).FYI, the main problem (for me) with flickery LEDs is the "phantom array" effect. It's also responsible for the DLP rainbow problem, which I definitely notice readily. It doesn't cause me headaches, but it is highly distracting.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: July 30, 2017, 12:28:24 pm
content: It's an issue with LCDs too. And was a major problem with CRT monitors. Towards the end of CRT tech we got higher refresh rates to help a bit. Drooling over those Trinitrons...If I was that bothered by it I'd look at changing the driver to constant current.It's not an easy fix for mains powered led bulbs that need to fit a small package.

author: MK14
author_rank: Super Contributor
timestamp: July 30, 2017, 12:51:39 pm
content: There are all sorts of complaints (in theory) about LED lighting.Not just flicker, but also limited colour temperature spectrum range, too much blue frequency spectrum (with all sorts of worries about that, as regards humans well being), and maybe other things too.My real complaint (sorry but it is POLITICAL). Is I don't mind the EU encouraging us to use LED lighting. But encourage us by advertising and/or discounts on LEDs and maybe gentle taxation on non-LED lighting.BUT to just make laws, so that most alternatives to LED lighting are BANNED. Is just draconian.If you can understand what I mean. It should be OUR choice, not some "invisible", somewhat unelected decision makers in the EU.I'd prefer to have the option, of using Halogen or even the older tungsten filament, lighting, where applicable.E.g. for choosing the BEST lighting for any Electronics Lab work area and working lights.The lack of colour gamut (or however I should describe the potentially limited light spectrum from LED lighting), can mess up colour identification (e.g. resistor colour band codes), and hence I presume, the potential quality of finer electronics work.Since Brexit has occurred. At least in the UK, it may potentially have different laws. But no real sign of it yet.

author: SeanB
author_rank: Super Contributor
timestamp: July 30, 2017, 12:58:46 pm
content: Well, just looked at the light I upgraded with some cheap eBay 10W buck converters ( 12-24VAC/DC in, 3-6V 900mA out) and 4 3W 4000K'ish cheap LED star clusters ( bought 50 as this was around the same price as 20 incl postage) running as 2 series strings of 2. Output flicker is a very tiny oscillation at 1MHz from the buck converter, 10mV on top of 700mV of output. Measuring device is another star LED used as a photodiode, so well matched to the emitter. Bright light this, a lot more light than the 50W halogen lamp that used to be in this Luci Abele desk lamp, and at 10W it runs a lot cooler as well. Hopefully running the chips at slightly lower level will be good for life as well.

author: Vtile
author_rank: Super Contributor
timestamp: July 30, 2017, 01:02:01 pm
content: Quote from: MK14 on July 30, 2017, 12:51:39 pmI share a secret. You can get good old tungsten heaters if you buy them with "for industrial use" stamp and they miracularly have usage hours of way above 1000 hours.

author: tooki
author_rank: Super Contributor
timestamp: July 30, 2017, 01:20:59 pm
content: Quote from: MK14 on July 30, 2017, 12:51:39 pmFWIW, the LED bulbs that have come out in the past year or two are vastly better than what was around even just 5 years ago. The color spectra are hugely improved, to the point that they are almost impossible to distinguish from incandescent.(I wear fairly thick glasses, and towards the edges, I get a sort of prism effect that breaks up the light into the spectrum. In older LED bulbs, a dot of light broke into distinct bands of red, green, and blue, or yellow and blue. The modern ones have a quite smooth spectrum without noticeable peaks or bands — just like incandescent. Not scientific, I know, but I don't have a spectrometer at hand.)

author: MK14
author_rank: Super Contributor
timestamp: July 30, 2017, 01:34:14 pm
content: Quote from: Vtile on July 30, 2017, 01:02:01 pmThanks for that. I did not know that there was such a work around, for the issue. I knew that "new old stock", bulbs of various forms, were obtainable on ebay. But did not realize there were (or had been) loop-holes.Unfortunately I have too much respect for my EU masters, to buy "industrial use", for use at home.http://www.dailymail.co.uk/news/article-2193792/Old-fashioned-lightbulbs-banned-EU-directive-sold-traders-loophole-allowing-renamed.htmlIt is fairly obvious (putting my electronics hat on), that there are various ways the LED lighting can be flicker free (because LEDs are flicker free, from DC or constant current sources. Even high frequency PWM, may be acceptable, if necessary). It just may need a modest increase in the cost of the LED lighting. Given that the electricity savings are huge (compared to tungsten bulbs) and they can potentially last a very long time, such as 10,000 hours.I can't see why that modest cost increase (to eliminate flicker, and ideally improve the colour gamut spectrum and maybe other improvements, such as blue light minimization). Can't be done.

author: SeanB
author_rank: Super Contributor
timestamp: July 30, 2017, 01:38:09 pm
content: DVD is a cheap spectrometer that works well. just tried on the cheap "Cree" led's, and they do have a very nice broad spectrum of light, a lot better than the older ones with 3 distinct emission spectrum blobs of blue, red and green.Of course if you are looking for old lights I have a collection of old ( as in pre war) lamps if you want some, all inside frosted glass in the most case and a number of carbon filament ones that are __NOT__ reproduction ones, but proper Siemens lamps. In reflector I have Poloish made R63 reflector ones as well.

author: MK14
author_rank: Super Contributor
timestamp: July 30, 2017, 01:43:12 pm
content: Quote from: tooki on July 30, 2017, 01:20:59 pmI only fairly recently started using LED bulbs. I got the best ones (via ratings and trusted brands by me, at least for lighting) I could determine, without paying a huge amount of money (i.e. quality ones, but not crazy expensive). Which seems to be the Philips ones (shown below). By and large, I'm rather pleased with them. But if I shake my hand in front of them, there is some noticeable flickering, between my fingers. Not too much, though.N.B. The UK does not seem to have the apparently wider range of LED brands, that e.g. the US has.I'm not 100% sure if the picture has IDENTICAL ones, to what I bought, many months ago. But it looks at least, very similar.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: July 30, 2017, 10:54:22 pm
content: Simple test; wave your hand back and forth in front of the light with spread fingers. If you see more than five there is a problem.I was alarmed to see that many LEDs are worse than CFLs for flicker, yet it's the flicker of CFLs which is supposed to cause headaches. Another 'green' fiasco if you ask me, products bad for our health rushed onto the market at the insistence of fanatical NGO lobbying. Likely, because they have stakes in the manufacturers.

author: wraper
author_rank: Unknown
timestamp: July 30, 2017, 11:01:13 pm
content: Quote from: IanMacdonald on July 30, 2017, 10:54:22 pmDecent led bulbs don't flicker. Most of flickering crap with capacitor droppers, no safety and awful efficiency comes from Chinese sellers as people try to skimp on them and order online from China.

author: IanB
author_rank: Super Contributor
timestamp: July 31, 2017, 12:12:52 am
content: Here's an example of a (non-flickering) recent purchase. Although it looks like there is no room for electronics in the base, there is actually a small circular SMT circuit board with various things on it including a 6 pin package of some sort.

author: tronde
author_rank: Frequent Contributor
timestamp: July 31, 2017, 12:36:55 am
content: Quote from: Vtile on July 30, 2017, 01:02:01 pmAnother secret:https://de.paulmann.com/leuchtmittel/halogenlampen/halogen-sockelset-230-v-33-watt-e14-klar/54920Ceramic adapter socket from E14 or E27 to G9 halogen and a suitable cover glass.Cheap halogen from China. No problem with safety (exploding) when using cover glass. If you dim them slightly, they last a long time.The opaque cover glass from Paulman is covered on the inside with a very fine white powder that gives excellent light ditribution.

author: PlainName
author_rank: Super Contributor
timestamp: July 31, 2017, 03:00:14 am
content: Aren't LEDs PWMd so they can be overdriven? The theory being that the eye sees the brighter light as bright, even though it is only there for a short time. Thus the light seems brighter but doesn't overheat because the duty cycle is low enough. (IOW, rather than being driven at their ratedforwardcurrent they are driven at theirpeakcurrent and then PWMd to bring the average current back to the forward equivalent. Result: same LED heat but brighter light.)Don't know about indoor filament replacements, but flicker used to be a very bad problem with car lights. Some manufacturers used a relatively low PWM frequency, and when static the (rear) lights looked fine, but when they crossed your vision at night (i.e. when you look around as is normal) you would see multiple images. I think the problem is that a dead part of the cycle would coincide with your eye briefly halting, so you'd see a series of steps rather than the smooth glide from an always-on light. Anyway, the problem with that (other than being deeply irritating) is that if confused you as to the position of the car.Lights in roadworks are particularly bad since you rely on them to see where the edge of the roadworks are. When each light has multiple instances, you can sometimes lose sight (sorry!) of where the real edge is. And, being cheap, roadwork lights flicker at a low frequency.Many people aren't affected by this, and the issue with car/roadwork lights is only apparent at night (possibly because there isn't a background to give your eye a reference). But perhaps there could be something similar with indoor lights if they are the only ones. In other words, suppose there is a single light that flickers at a low enough frequency for you to notice when something moves. It will seem OK but when you look around, or your eyes move when , for instance, you read a book, your eyes may get tired quickly. However, if there are more than one such light it's probably that the flicker frequencies are slightly out, so they won't all be off, or on, at the same time. Thus no effect.Personally, the car lights thing is very bad for me. I've replaced my office lights with LEDs and have no problem at all. Don't know if they flicker, though. Never bothered by fluorescent lights either.Edit: Just checked and my fluorescent replacement LED tubes do flicker at 100Hz (this is the UK where mains is 50Hz).

author: georges80
author_rank: Frequent Contributor
timestamp: July 31, 2017, 04:24:00 am
content: Quote from: dunkemhigh on July 31, 2017, 03:00:14 amNo. Eyes integrate over time. So, running 1x average current or 2x current at 50% duty cycle will look essentially the same in brightness to the eye.Don't get confused by PWM as per the DC : DC switcher (which is typically in the 100kHz - 2MHz range) and the slow speed dimming PWM.Buck/Boost/Buck-Boost etc drivers will run at high frequency, with just a few uF of capacitance you have essentially flicker free DC feeding the LEDs. Some drivers will dim by changing the drive current (i.e. fully current regulated dimming). These will have no flicker.Some drivers will use slow speed PWM (which typically gives a much higher dynamic range) to dim. This PWM is typically a few hundred Hz (or more) depending on the dimming circuit controlling the DC : DC switcher. The PWM dimming can be a bother for video cameras if the frequency beats with the video frame rate - you can get various banding issues - equivalent to the old days of using a video camera to record the image on a CRT.Anyhow, PWM will not provide 'more' visible light for less heat/current/power.High current pulses can be used with some LEDs (read spec) to achieve a bright 'flash' for cameras etc. This exceeds average max current, but as long as the current pulse doesn't violate the spec (i.e. damage to bond wires or super hot spots on the die) then you can get a large short bright 'flash'.cheers,george.

author: PlainName
author_rank: Super Contributor
timestamp: July 31, 2017, 04:34:19 am
content: QuoteI think you're mistaken, and this experiment would seem to bear me out:https://bryanduxbury.com/2013/12/02/over-driving-leds-for-brightness/Cutting to the chase at the bottom, the 18mA average at 10% duty cycle give more or less the sameperceivedbrightness as 30mA full on. I think the eye sees the peak over time rather than average.QuoteI am not, but thanks for pointing it out.

author: georges80
author_rank: Frequent Contributor
timestamp: July 31, 2017, 05:10:56 am
content: Nope. Only works if the strobe rate is slow enough that the eye can see the bright flash. There's also an LED issue, some will not light at low current and require a drive current beyond a certain level to 'turn on'. So, low average constant current won't turn a LED on, but short higher current pulses will - so in that case it appears that the PWM 'version' is brighter.But, in general, for a LED running at some reasonable current level for a light bulb replacement (i.e. 100's of lumens) low freq PWM will not make it look brighter than driving at the equivalent average current.cheers,george.

author: Someone
author_rank: Super Contributor
timestamp: July 31, 2017, 05:27:41 am
content: Quote from: dunkemhigh on July 31, 2017, 04:34:19 amThats not much evidence for the supposed effect completely missing any measurements of the actual brightness or even power. Instead we can point you to a real source:https://www.jstage.jst.go.jp/article/jlve/32/2/32_2_161/_pdfNoting that their "improvements" are quite slight and only when compared in luminous flux, comparing actual power dissipation (even of just the LED!) the DC driver example is the clear winner.Quote from: georges80 on July 31, 2017, 05:10:56 amThere is still ongoing research in the area and a lot of the data isn't public, but there are examples where the enhancement effects can be measured beyond the flicker fusion threshold. More gains can usually be found by driving the LED at its most efficient current and improving cooling of the die.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: July 31, 2017, 06:43:10 am
content: Quote from: wraper on July 30, 2017, 11:01:13 pmIf you can find ones thataren'tmade in China regardless of brand, you are doing well.

author: Halcyon
author_rank: Unknown
timestamp: July 31, 2017, 08:59:27 am
content: The media love to pump things like this up, but there is some truth to it.I specifically chose high quality LED lights for my house that had low flicker specs. All lights exhibit some flicker, most aren't visually perceivable, but I've walked into some houses with cheap Chinese LED down lights and have had a constant flicker in my peripheral vision just walking around (like earlier DLP projectors).I foundLED Benchmarkan excellent website.Some of the "cheaper" lights surprised me with their performance, but you can't go wrong with the good stuff such as Philips.

author: PlainName
author_rank: Super Contributor
timestamp: July 31, 2017, 10:27:20 am
content: QuoteWhich agrees with my supposition. Indeed, they say:QuoteFrom Britannica:QuoteThis is what you're suggesting, I think, and that's specifically what the paper you referred to didn't see.P.S. feel free to post more links that reinforce my suggestion

author: tooki
author_rank: Super Contributor
timestamp: July 31, 2017, 10:33:01 am
content: Quote from: dunkemhigh on July 31, 2017, 03:00:14 amThat is the "phantom array" effect I mentioned in an earlier post. Like you, I am very sensitive to it. It doesn't cause headaches, but I find it extremely distracting.

author: PlainName
author_rank: Super Contributor
timestamp: July 31, 2017, 10:38:09 am
content: It sounded familiar so I thought it might be the same thing, yes

author: chris_leyson
author_rank: Super Contributor
timestamp: July 31, 2017, 10:43:49 am
content: As a side note, cmos image sensors make good spectrometer diffraction gratings albeit 2D though.

author: tooki
author_rank: Super Contributor
timestamp: July 31, 2017, 10:46:13 am
content: Quote from: dunkemhigh on July 31, 2017, 10:38:09 amAnd yes, I want to kill the automotive engineers that thought that 100Hz PWM would be fine for tail lights, probably since it's above the 60Hz flicker fusion threshold, despite that being inapplicable.

author: Someone
author_rank: Super Contributor
timestamp: July 31, 2017, 11:38:58 am
content: Quote from: dunkemhigh on July 31, 2017, 10:27:20 amUnlike your glossing over the data I pointed you to a well presented experiment which you've swallowed hook line and sinker to reinforce your misguided views. I specifically called out their results and how they showed the opposite effect of improving luminous efficacy:Quote from: Someone on July 31, 2017, 05:27:41 amThey only found an improvement for pulsed drive when comparing the perceived brightness against the luminous flux of the two drive conditions (which was poorly measured), when measuring the power used to produce the illumination the DC drive was clearly superior. Again you're welcome to find other data but most of it is not public or behind paywalls.

author: Kjelt
author_rank: Super Contributor
timestamp: July 31, 2017, 12:09:15 pm
content: Don't know if this has been mentioned yet but most white leds use a blue led and yellow phosphor to generate a more broad spectrum white in diverse color temperatures.The phosphor acts as in a fluorescent tube it will also make any flicker less visible.Never ever buy RGB led only based lamps for white light in livingspaces, it is just awfull and the colortemperature variates between each bulb, some are even greenish or pinkish not white at all.The more expensive versions do however have combinations of RGBW leds and they are ok.

author: Zbig
author_rank: Frequent Contributor
timestamp: July 31, 2017, 12:33:10 pm
content: My girlfriend had some mini LED replacement bulbs installed in place of original halogen ones in the light fixtures in her bathroom. Due to the size constraints, I doubt there's anything other than some LEDs and maybe some dropper resistors in them. While the flicker was immediately obvious to me, she doesn't seem to notice. When taking a pee for the first time after the lighting change, I first freaked out then bursted out laughing when I saw the stream of urine coming down as a string of individual beads suspended in the air due to stroboscopic effect. I kid you not, that was trippy.

author: Halcyon
author_rank: Unknown
timestamp: July 31, 2017, 12:51:25 pm
content: Quote from: Zbig on July 31, 2017, 12:33:10 pmQuote of the month for sure!The crazy thing is, I completely understand what you mean.It reminds me of those light guns that mechanics use to syncronise the output light to the spark of the ignition coil to view defects in the timing belt etc...Just don't sneeze...

author: MK14
author_rank: Super Contributor
timestamp: July 31, 2017, 02:20:07 pm
content: Quote from: tronde on July 31, 2017, 12:36:55 amThat's another interesting way round the upcoming changes to the bulb availability situation. Thanks!Some people say halogen lights, make the best Electronics Lab lights.Because I've got advanced warning, about this upcoming law change, so around about 2018, Halogen bulbs (presumably bigger, mains ones), will be outlawed in the EU. I can stock up on them.Despite all the negative things people are saying about LEDs in this thread (including and especially by ME!). They have got a number of advantages as well. I really like that they produce little heat, and can last a very long time.I.e. 500 Watts worth of tungsten lamps, produces a lot of nice light (via multiple bulbs to make it 500 watt, as labs like nice bright lights).But it also makes the room, potentially uncomfortably hot, which I would NOT like, and is expensive to run.But (very approximately), only 100 watts (maybe even less), worth of LED bulbs, can make the same amount of light, mostly WITHOUT the huge heat. In summer, it can be especially important.Since we (this forum) are into electronics, I'm sure I/we can either get flicker free LEDs (or make them so). Hopefully relatively flicker free LED bulbs, will always be available (until they are replaced by the next technological marvel).Quote from: IanB on July 31, 2017, 12:12:52 amI wonder if it is "flicker free", because of the special 'dimmable' capability built into it ?I.e. It is made dimmable by special averaging/storage capacitors, hence the lack of flicker.

author: FrankBuss
author_rank: Unknown
timestamp: July 31, 2017, 03:00:10 pm
content: Quote from: MK14 on July 29, 2017, 07:34:50 pmHow do you know that more expensive LED bulbs last longer? They could be the same cheap products, just sold more expensive.

author: MK14
author_rank: Super Contributor
timestamp: July 31, 2017, 03:36:30 pm
content: Quote from: FrankBuss on July 31, 2017, 03:00:10 pmYou can (in theory) potentially get cheap LED bulbs, which are rather good quality and may last a long time, reliably. As with many things. But if you buy cheaper and cheaper ones, and don't check the quality/reliability/etc of them with reviews or other sources.You might end up with something which is poorly made, and doesn't last very long. It maybe even dangerous as regards fire hazard and even electric shocks.One of BigCliveDotComs LED bulb videos, seems to agree with BOTH of us!He seems to be saying, that the original £1 LED bulb from PoundLand in the UK, skimped on the heatsinking. So only gave a significantly poor LED bulb life. Which is why I was effectively saying, that cheap ones can be poor qualtiy = poor life expectancy and reliability.BUT PoundLands supplier, has improved the design (still at £1 each). So now it is apparently decently heatsinked, and so does (or should), last a lot longer.The main two reasons I try and get quality (not necessarily cheap), along with (ideally) a good quality brand as well. Is because I want as much of the colour gamut spectrum, which quality ones seem to have engineered into them. But cheap onesmightnot. Reviews seem to imply that cheap and low quality ones, DON'T have a good colour gamut spectrum. But higher end LED bulbs, can have good colour gamuts.The other reason, is I have heard horror stories, of poor quality LED bulbs catching on fire and/or smoking badly.I use to have lots of compact florescent bulbs, which as they burn out are tending to be replaced by LED bulbs, by me.At least one set of my compact florescent bulbs, many years ago. Did actually fail, either at about a hundred or few hundred hours and/or when accidentally switched on and off, a couple of times, very quickly.During at least one of the failures (perhaps as many as 2 or 3 in total), I got a rather bad smell, and was very worried about the fumes that had filled the room (was it bad for my health ?).I abandoned using those (yes I admit it, not only VERY cheap, but they were considerably price reduced as well) compact florescent bulbs brand (they were branded from one of the major UK supermarket chains), and if I remember correctly, I binned all the other (real cheapo) ones, as well.To be clear I only binned that particular BRAND, not other cheap bulbs I had, from other sources.That incident (compact florescent bulbs), made me say to myself, I wouldNOTbuy those or any cheap bulbs (compact florescent at the time), again. Therefore, I'm using that same lesson, in avoiding cheap LED bulbs. But if a cheap brand gets great reviews or is from a reputable brand (e.g. Philips), I will have to reconsider the situation.Bear in mind, LED bulbs, are relatively new on the market. So I have not had much time, to gain experience with them. The reason why I only very recently started using them, was because I wanted them to improve and get cheaper, before getting them. Many years ago, they were some huge price (I can't remember exactly, but something like >=£20 each), and not very bright either. So I continued with compact florescent ones.Whereas nowadays, they can be very bright, and very cheap as well.

author: Yansi
author_rank: Super Contributor
timestamp: July 31, 2017, 04:43:54 pm
content: Quote from: IanB on July 29, 2017, 08:02:41 pmThe persistence of the LED phosphor is negligible, zero.

author: tronde
author_rank: Frequent Contributor
timestamp: July 31, 2017, 05:34:26 pm
content: Quote from: dunkemhigh on July 31, 2017, 03:00:14 amThey use PWM because the colour of any LED will change with the current. When you use PWM and a constant current source, you will remain the colour even when the light is dimmed.

author: tronde
author_rank: Frequent Contributor
timestamp: July 31, 2017, 05:45:28 pm
content: Quote from: MK14 on July 31, 2017, 02:20:07 pmThe Paulman stuff is very good as I can see it. I managed to get them before they stopped selling them here. I guess it was because of low volume, but since you are in the EU they should be easy to get.As of today, halogen will be banned from 01.09.2018. Some types are already banned, but not G9. Initially they should have been banned in 2016.

author: PlainName
author_rank: Super Contributor
timestamp: July 31, 2017, 06:49:32 pm
content: Quote from: tronde on July 31, 2017, 05:34:26 pmI was thinking about other applications (for instance, car position lights) where the LEDs aren't typically providing a broad spectrum. Also where they are not illuminating something but are viewed directly. 'Traditional' usage, if you like.

author: Kjelt
author_rank: Super Contributor
timestamp: August 02, 2017, 02:46:00 pm
content: 3000Hz boundary of human flicker visionhttp://www.businessinsider.com/the-scientific-reason-you-dont-like-led-bulbs-2017-7