Replacing Neon Lamp with LED - Page 1
Forum section: electronics / projects

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 18, 2021, 05:09:33 pm
content: I have a device here that I wish to replace the failed Neon power indicator.It has no low voltage DC as it is a mains appliance, so it needs to run from the mains voltage.I have done a lot of research and learned about capacitive drop supplies. I have dismantled and reverse engineered a few LED light bulbs and learned the equations for capacitive reactance.I have finally settled on this design which supplies the LED with 2V 10mA from the 240V AC Mains.It works brilliantly and the LED should last a long time on 10mA.Is there any improvement that can be made to this design?My main concern about putting a fuse on it, as it is directly across the mains. Could I perhaps move R2 to the other side of C1 and change it to a fusible resistor? How would I calculate which fusible resistor?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 18, 2021, 05:17:18 pm
content: The 100uf cap is overkill.Do you need as much as 10mA?For a power indicator, a low-current LED and series resistor for 1-2mA could be fine. Use a fusible reistor for R2. Fusible resistors don't have a current rating, they are just specced to not catch fire if they pop.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 18, 2021, 05:27:50 pm
content: Quote from: mikeselectricstuff on October 18, 2021, 05:17:18 pm100µF is just one I had lying around. I also have 10µF would that suffice for C2?The LED is a standard 20mA 2V LED. Running it at 20mA was a bit too bright but I found at 10mA it looks about right in a dark room.If I replaced R2 for a fusible resistor would it be better to put it before C1?And how would I spec the correct wattage of fusible resistor?I notice in the regular LED light bulbs they just use 0.25W fusible metal film resistors, but they are before the dropper capacitor.

author: tunk
author_rank: Super Contributor
timestamp: October 18, 2021, 05:36:30 pm
content: You could also take a look at this:https://youtu.be/Q23uh7AjjXw

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 18, 2021, 05:48:40 pm
content: Quote from: tunk on October 18, 2021, 05:36:30 pmYes I did see Big Clive's video alreadyThat is where I got some of my information from.I decided to add the smoothing capacitor as the flickering (although minor) was annoying and noticeable in the dark.And I came across the idea for the Zener Diode just to help protect the circuit from High Voltage spikes on the mains.

author: james_s
author_rank: Super Contributor
timestamp: October 18, 2021, 06:22:32 pm
content: Wouldn't it be easier to just replace it with another neon lamp? This LED retrofit is a lot more complicated with many more potential failure points, for what benefit?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 18, 2021, 06:34:54 pm
content: Quote from: james_s on October 18, 2021, 06:22:32 pmPerhaps it would be, but then I wouldn't learn anything that wayThe benefit... Education.

author: TimFox
author_rank: Super Contributor
timestamp: October 18, 2021, 07:43:24 pm
content: In general, the 100 uF capacitor to reduce flicker would be more effective if it saw more series resistance feeding it. In your drawing, on positive cycles after the bridge, it is almost shorted out by the forward current of the LED (or the Zener). You could put the 100 uF directly after the bridge, reduce the existing series resistor and move the difference to between the 100 uF capacitor and the diodes.

author: Benta
author_rank: Super Contributor
timestamp: October 18, 2021, 07:58:05 pm
content: If you think that a major circuit for lighting an indicator lamp is great, fine with me.I'd go for the neon lamp plus resistor every time.Anyway: your circuit is not that bad but is has some flaws. The input circuit is OK, provided the bleed resistor is a high voltage type (eg, Vishay VR37), and the series resistor is current pulse resistant (eg, wire wound).Bridge rectifier is also OK. But from there on it goes downhill.1: why the 2 V Zener? (where on earth did you find that one?). LEDs are not voltage controlled, but current controlled.2: 100 uF is way overkill, but you've already explained that point.A good design would be, say 4.7 uf, a 4.7 V Zener and a series resistor for the LED to set the current.But I'm not a friend of cap-drop powering of anything. The only isolation you have in this design is the resin of the LED.On top of that, I believe this forum has a ban on cap-drop mains powering.

author: David Hess
author_rank: Super Contributor
timestamp: October 18, 2021, 08:41:38 pm
content: Do not really need the bridge rectifier except for efficiency. Keep the anti-parallel diode to protect the LED from reverse voltage, or use an anti-parallel dual LED.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 18, 2021, 08:45:29 pm
content: Quote from: David Hess on October 18, 2021, 08:41:38 pmBut you do at least need an inverse-parallel diode across the LED.You don't need the zener - the high impedance of the dropper cap makes it effectively a current-source

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 18, 2021, 09:01:14 pm
content: Quote from: David Hess on October 18, 2021, 08:41:38 pmInitially I tried it with an inverse diode and also an inverse LED. However the flickering was very obvious when using both of these methods.Considering the 1N4007s were less than £0.01 each and the LED has no noticeable flicker with it, I think the full bridge rectifier is perfectly justified.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 18, 2021, 09:04:11 pm
content: Quote from: Benta on October 18, 2021, 07:58:05 pmAll the store-bought LED light bulbs I dismantled use this same basic layout:Capacitive drop with bridge rectifier and smoothing capacitor. and a Zener diode in parallel with the LED(s). The only thing they had which mine didn't is a fusible resistor which I need to add before the capacitor.

author: Zero999
author_rank: Super Contributor
timestamp: October 18, 2021, 09:24:45 pm
content: Orange LEDs have poor efficiency. Use a phosphor converted LED, which consists of a blue/violet/UV LED with a fluorescent material, to produce orange light. Unfortunately, the only ones I can find are these, which can only be bought from Rapid Electronics, in the UK. TME also sell them, but they no longer sell to individuals in the UK.http://www.optosupply.com/newproduct/detail.asp?id=1898The orange peach colour should be fairly close to a neon lamp, especially if it has a filter.https://www.tme.eu/en/details/oscg4l5111a/tht-leds-5mm/optosupply/https://www.rapidonline.com/Catalogue/Product/55-9177The LEDs linked to above should give a nice bright light, at nor much more current, than a neon lamp. Use an SMT bridge rectifier and two 68k current limiting resistors in series to drive it.

author: analogMensch
author_rank: Newbie
timestamp: October 18, 2021, 09:27:12 pm
content: Make sure your C1 is a X2 type, so it can handle pulses on mains.I build my mains driven LED status lights also like this with a FBR, but I use a 5.1V zener, 25uF smoothing cap and a 2k or 4.7k resistor in series with the LED. Always works like charm!

author: Benta
author_rank: Super Contributor
timestamp: October 18, 2021, 09:28:44 pm
content: @Zero999, has your account been hacked?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 18, 2021, 09:37:59 pm
content: Quote from: analogMensch on October 18, 2021, 09:27:12 pmYes it is an X2 typeHave you got a schematic for one of your ones please so I can see?

author: james_s
author_rank: Super Contributor
timestamp: October 18, 2021, 10:24:42 pm
content: Quote from: Benta on October 18, 2021, 09:28:44 pmWhy do you keep responding to threads like this? It's starting to sound like paranoid delusions. What makes you think his account was hacked? Because he provides some links to the places where he bought some of the LEDs he is describing? There is no rule against doing that, it's not like Rapid Electronics is some random sketchy Chinese company.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 18, 2021, 10:35:18 pm
content: Yes the 100uF is a bit ott. Make sure the 100n is class X (don't say no one told you) and R2 is a fusible resistor. The diode bridge is also overkill. A reverse polarity diode acros the LED is sufficient. Better still buy a new neon or a ready rolled mains rated LED panel indicator. Trawling your options is highly educational.

author: floobydust
author_rank: Super Contributor
timestamp: October 19, 2021, 03:37:50 am
content: OP your circuit is very close to LED nightlights. Actually difficult to design.The input needs a say 100-220R flameproof, fusible resistor that tends to fail open if you power up at a mains peak, the inrush is quite high.Thedropper capacitoris generally huge for ones rated for the application.It's better to use the zener at say 9V or 12V and then a resistor to drop that down for the LED. You can use a much smaller cap and get no flicker, compared to being right across the LED. The electrolytic cap's ripple current is high and can shorten life.Without any clamp zener, I had an LED fail open-circuit and the capacitor explodedWhat I do to replace neons, if flicker is not a problem, is a resistor and LED with reverse-diode across it. NOT SERIES diode, that fails fast.For no flicker, a bridge rectifier is good enough for 100/120Hz harder to notice, and just a resistor for the LED. Even 1mA can be quite bright with high efficicency LEDs.

author: james_s
author_rank: Super Contributor
timestamp: October 19, 2021, 05:12:46 am
content: Quote from: Benta on October 18, 2021, 07:58:05 pmSince when?Maybe you're thinking of one of those weenie forums where they don't even let people talk about anything mains powered.People have discussed far more dangerous things than transformerless power supplies here.

author: tooki
author_rank: Super Contributor
timestamp: October 19, 2021, 08:43:10 am
content: Quote from: Benta on October 18, 2021, 07:58:05 pmJust because people often reply that capacitive droppers are a bad idea (or outright refuse to help someone who asks how to do it) doesn’t mean the topic is banned. The reason people often refuse to provide the information is that the people asking about them are generallyobviouslynot skilled enough to do it safely. (Like how it’s invariably absolute newbies who want to look at mains with their new oscilloscope.)In terms of content, the forum really only has two or three rules, which is that it has to be about electronics and may not be political. Blatant piracy is also not tolerated, though that’s really a gray area if you consider how much discussion there is about unlocking device features. :p

author: Zero999
author_rank: Super Contributor
timestamp: October 19, 2021, 09:09:24 am
content: Quote from: james_s on October 18, 2021, 10:24:42 pmExactly.I haven't bought those exact LEDs, but have purchased similar items. It's true, phosphor converted LEDs are often more efficient, than those which directly produce the required wavelength for colours in the middle of the visible spectrum: yellowish green, to orange. This is more likely applications, where the higher volt drop is a non-issue and using a lower volt drop device would just result in more heat in the resistor/linear regulator.

author: floobydust
author_rank: Super Contributor
timestamp: October 19, 2021, 06:18:38 pm
content: I appreciate new LED colours- no need to give someone flak for that.Kingbrightoffers some as well.Overall, I find mains capacitive droppers simply don't last. For LED nightlights, you can do LTSpice sims and see the peak currents are high which shortens the life of almost all the components including the LED. I've taken apart quite a few (that have regulatory approvals). You need a fuse, flameproof resistor, dropper-rated capacitor and then a scheme for low flicker. The one where the electrolytic cap exploded stunk up the house.I've also put three LED's in series for higher brightness.

author: David Hess
author_rank: Super Contributor
timestamp: October 19, 2021, 08:30:33 pm
content: The well designed ones I have encountered lasted longer than the neon bulbs they replaced, but I prefer the look of a neon bulb.A zener shunt can be used to limit the voltage across an LED and current limiting resistor. The demands on the voltage dropping capacitor are severe so a high quality part is required for reliability.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 19, 2021, 08:33:44 pm
content: I've found running two LEDs in parallel, with the polarity flipped, provides less flicker and each one protects the other from excessive reverse voltage. Cap drop works fine but is prone to passing line transients so needs some series resistance and small cap. I use this circuit for turntable strobes along with a pair of zeners so the duty cycle of the LEDs is limited to a shorter portion of the line cycle and you get sharper strobe disk bars. Not needed for a power light.

author: Benta
author_rank: Super Contributor
timestamp: October 19, 2021, 08:40:09 pm
content: Quote from: james_s on October 18, 2021, 10:24:42 pmWhy are you so aggressive?This thread is about a neon lamp indicator being replaced with an LED.Suddenly, a known user shows up with pictures of Architectural/Designer/Mood lighting that look like 100% advertising to me.My question was in no way meant as provocative or challenging, but more a result of confusion, as I know that the said user is very good at staying on topic in a thread, and always provides valuable insights.Concerning: "Why do you keep responding to threads like this? It's starting to sound like paranoid delusions.", that's perhaps the most unfair I've ever seen.You should be ashamed of yourself for that statement. Feel free to go through my posts history.

author: Zero999
author_rank: Super Contributor
timestamp: October 19, 2021, 09:50:13 pm
content: Quote from: Benta on October 19, 2021, 08:40:09 pmIf you read mypostproperly, you'll find I did suggest a specific LED which will give a similar colour to a neon lamp, nothing about architectural/designer/mood lighting.Those LEDs aren't widely available. Another option is to use a warm white LED, which might be acceptable, if the neon has a yellow/orange filter.

author: Benta
author_rank: Super Contributor
timestamp: October 19, 2021, 10:06:56 pm
content: Quote from: Zero999 on October 19, 2021, 09:50:13 pmYes, and if you read the thread, the OPneverrequested a "neon colour" LED. Your post looked like an advertisement, OK? 'Nuff said.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 19, 2021, 10:45:42 pm
content: Quote from: Conrad Hoffman on October 19, 2021, 08:33:44 pmPretty sure I've seen LEDs with two die that do this internally

author: Benta
author_rank: Super Contributor
timestamp: October 19, 2021, 11:04:38 pm
content: Quote from: mikeselectricstuff on October 19, 2021, 10:45:42 pmInteresting.I've never seen such LEDs myself, but often optocouplers. Do you have lniks/references? Thanks.

author: langwadt
author_rank: Super Contributor
timestamp: October 19, 2021, 11:38:56 pm
content: Quote from: Benta on October 19, 2021, 11:04:38 pmobsolete but;https://www.elfadistrelec.dk/Web/Downloads/86/20/Lx-bipolar_eng_tds.pdfif you can live with the mixed color there's crap tons of dual color leds that'll work

author: tooki
author_rank: Super Contributor
timestamp: October 20, 2021, 12:04:50 am
content: Quote from: Benta on October 19, 2021, 10:06:56 pmNo, itreallydidn't. It read like a standard, legitimate "here's a product I'm familiar with, maybe this will help. here's the links" post, the likes of which there are thousands and thousands on the forum.And your "architectural lighting" is literally the standard way LED colors are shown: a single LED uplighting a white surface. I do see the visual similarity to some architectural lighting, but if you shopped for colorful LEDs you'd have recognized the image for what it is.Quote from: Benta on October 19, 2021, 11:04:38 pmSee attached datasheets for some currently available on digikey (plus one obsolete Fairchild part).

author: SeanB
author_rank: Super Contributor
timestamp: October 20, 2021, 07:52:41 am
content: Simplest replacement is to use one of the high efficiency LED's , and no capacitive dropper. Simply use the same value resistor as the neon used, but have a bridge rectifier after it. I tend to use 4 12V zener diodes, simply because I have a lifetime supply of them, so they are often used as regular diodes where appropriate. Then a capacitor, around 10-100 uF 16V, and then a series resistor, one tenth of the main resistor, to feed the LED. Safe, and you can use 2 resistors in series on the input side, one in each leg, whose combined value is somewhere between 47k and 220k, which is typical for most neon lamp current limiters. Simple, has no failure mode other than the electrolytic going open circuit, which does not matter as it just flickers, and will have a lifetime equal to that of the LED, or a century in most cases, as the LED is being run at under 1mA. High efficiency LED's in red or green at 1mA are incredibly bright, and are one of the more common type available these days.

author: Zero999
author_rank: Super Contributor
timestamp: October 20, 2021, 11:59:02 am
content: Quote from: Benta on October 19, 2021, 10:06:56 pmHe asked for advice about replacing a neon lamp with an LED. It should be obvious, unless you're retarded, that LED should be a neon colour to emulate a neon lamp. No one else thought my post looked like an advertisement. Only you.Quote from: mikeselectricstuff on October 19, 2021, 10:45:42 pmI'm pretty sure this LED is really three connect in series.https://www.rapidonline.com/truopto-os5mpl56d1a-4-8mm-warm-white-9v-3000k-22lm-water-clear-130--55-9126

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 20, 2021, 03:29:04 pm
content: I have taken into account what was posted here and modified my design accordingly. Please see the v3 schematicI can only get 2.4V Zeners at the moment. Should be close enough? The max rating of the LED is 3V and the continuous is 2V.I am getting approx 7mA current draw through the whole circuit. (ammeter in series with Live wire).I am also getting approx 7mA at the LED. (ammeter in series with LED)By my calculations 7mA at 253V is 1.771W so I will need a 100Ω 2W metal film fusible resistor?2W seems excessive, the fusible resistors in the commercial lights I have are the small 0.25W metal film resistors? Am I calculating something wrong here?

author: TimFox
author_rank: Super Contributor
timestamp: October 20, 2021, 03:42:41 pm
content: The Zener is redundant and can be deleted, so long as the voltage across the LED never goes negative (reverse bias). The LED, driven from a reasonable source impedance, will limit the voltage across itself. LEDs, like Zener and forward-biased diodes, should never be driven directly from a constant-voltage source.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 20, 2021, 03:55:48 pm
content: Quote from: TimFox on October 20, 2021, 03:42:41 pmIf the Zener is redundant then I have a question; Why do they include them in LED light bulbs from the store?I have taken apart 6 different models and makes so far and they all have a capacitive dropper with a Zener diode across the LEDs in this same configuration.I thought it is to protect from sudden voltage spikes on the mains?

author: TimFox
author_rank: Super Contributor
timestamp: October 20, 2021, 04:14:26 pm
content: Belt and suspenders, maybe? If a spike gets through the capacitor (which will preferentially pass fast spikes), the Zener might have a higher capability to survive the energy in the spike, but will still (transiently) over-voltage the LED. Because of spikes, the series resistor is necessary in such simple capacitance-dropper circuits to limit instantaneous current.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 20, 2021, 04:22:24 pm
content: OK well it seems like this is a good design then unless anyone else can point out any other design flaws?Regarding the Wattage of The fusible resistor though. Which will I need?7mA at 2V - at the LED is 0.014WHowever 7mA at 253V (240 +10%) - at the live mains input is 1.771WSo which would it be?I believe I am miss-understanding something here.

author: Benta
author_rank: Super Contributor
timestamp: October 20, 2021, 04:32:37 pm
content: A comment to your latest schematic: you're still treating the LED as a voltage controlled device. It is NOT. You need to control thecurrentthrough the LED.

author: Vovk_Z
author_rank: Super Contributor
timestamp: October 20, 2021, 04:33:32 pm
content: Quote from: paul_g_787 on October 20, 2021, 03:29:04 pmIt seems to me over-complicated. If LED 50 Hz blinking is ok (usually it can't be seen by eyes), then the circuit may contain only three parts: bright (ultra-bright) LED (1-2 mA), series 1N4007 diode and series 47-200k 1W resistor.It may contain a diode bridge instead of a singe rectifying diode, so blinking will be 100 Hz, the same as for neon lamp. The main thing is to have a LED diode bright enough with a low (1-2 mA) current (so we could use a series voltage drop resistor instead of a cap).

author: TimFox
author_rank: Super Contributor
timestamp: October 20, 2021, 04:44:11 pm
content: Quote from: paul_g_787 on October 20, 2021, 04:22:24 pmThe fusible resistor should be specified as the fuse current: the current it can safely pass and the higher current that is required to blow it.The resistor itself should be rated for the power dissipated when the maximum current passes through it, not the entire circuit. If you know the currentthrough the resistoris 7 mA, then the power inthat100resistor is only 5 mW. The power in the other resistor, 1000, at 7 mA is 50 mW.

author: StillTrying
author_rank: Super Contributor
timestamp: October 20, 2021, 05:31:46 pm
content: Simulate it.It works OK, 9 VDC across the 47u and 6.2 mA through the LED, until some 100V spikes come along.A 12 or 15V zener across the cap seems safer, that zener would clamp 100s of mA during mains voltage spikes, so probably make it a 1W one.The zener across the LED doesn't do anything useful.

author: Benta
author_rank: Super Contributor
timestamp: October 20, 2021, 07:01:32 pm
content: Quote from: paul_g_787 on October 20, 2021, 03:29:04 pmI attach the schematic of a cap-drop supply I designed 15 years ago. It's laid out for a bit higher current than your LED driver, and has been operating in many devices with 100% reliability.Ignore the lower and the right parts of the drawing, they're irrelevant to your application.I went back over my design notes:R1: 470 kohm, Vishay VR37 (cap bleed resistor)R2: 330 ohms, Vitrohm BW234, (wirewound startup current limit resistor)D1...D4: 1N4007Z1: 1N592xB, ONSemiconductor (voltage depending on number of LEDs, for a single LED I suggest 5.6 V)R3: any 0.3 W resistor, value dependent on Z1 and desired LED current and colorC1: 470 nF 305 VAC X2 (this is chosen for 35 mA IIRC, you need a lower value)C2: 220 uF, 16VThis lists the critical parts. You have to consider the following:1: at turn on, the only thing limiting inrush current at peak AC voltage is R2, and it will have to withstand >1 A peak current.2: the same is true for for C2 and Z1. IIRC, that explains the relatively high value of C2 and the high power rating of Z1.3: the bleed resistor avoids C1 discharging through a person touching the mains plug prongs after unplugging.R1 and R2 are pure loss, of course, and their values need to be weighted. If you only need 7 mA, R2 can be increased, with lower demands on C2 and Z1 making them smaller and cheaper.I'm not too proud of the design, I dislike cap-drop solutions. It was only chosen because it was the simplest and cheapest, not due to performance.Hope this helps, as I said, it's a tried-and-tested, reliable design.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 20, 2021, 07:13:45 pm
content: Quote from: TimFox on October 20, 2021, 04:44:11 pmAh I see I am thinking of it back to front.So for example that means at 7ma, if I were to use a 0.25W resistor it would need to be 5.1KΩ correct?Or I could use a 2.5KΩ metal film resistor to provide 10mA of fusing at 0.25W?

author: TimFox
author_rank: Super Contributor
timestamp: October 20, 2021, 07:32:21 pm
content: A 5.1 k resistor would be just within its power rating of 1/4 W at 7 mA current through it.In general, it is good practice to derate resistors, typically to no more than 1/2 of the rated power, or do a careful calculation to ensure that the worst-case power in the part will not raise its temperature above what your use requires.That's not the same as its fusing rating. For example, the TE series FRN leaded resistors are rated to blow in 60 sec at 16x rated power, or 15 sec at 32x rated power.The power rating is for < 70oC ambient temperature, derated above according to the graph.https://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet%7F1773218%7FE%7Fpdf%7FEnglish%7FENG_DS_1773218_E.pdf%7F1625879-2

author: james_s
author_rank: Super Contributor
timestamp: October 21, 2021, 06:18:56 am
content: Quote from: floobydust on October 19, 2021, 06:18:38 pmI have several LED nightlights that have capacitive droppers. The LEDs were cheap and wore out within just a few months so I replaced them with some non-phosphor LEDs I had in various colors. That was probably 10 years ago and not one of them has failed since.

author: rfclown
author_rank: Frequent Contributor
timestamp: October 22, 2021, 05:48:37 pm
content: I've never dealt with trying this before, but when I read this thread I wonder what I'm missing. It seems to me that a current limiting resistor and back to back diodes is all that would be needed. I just grabbed two LEDs out of a bag of miscellaneous parts (didn't know what colors they were). They both measured about 2.7V and I checked that both would light with 1mA of current. Figured that 100k would give me roughly 1mA. Looked in resistor bin and saw 1/2 watt 47k parts, so I grabbed two. Wired together. I don't see any flickering.

author: Benta
author_rank: Super Contributor
timestamp: October 22, 2021, 06:26:41 pm
content: People don't have the same eyes.Tip: try holding the LEDs in your peripheral vision instead of looking directly at them. Odds are you'll see the flickering. There are also people that see 100 or 120 Hz flickering directly in their field of vision.

author: BrokenYugo
author_rank: Super Contributor
timestamp: October 22, 2021, 06:52:22 pm
content: Quote from: langwadt on October 19, 2021, 11:38:56 pmThey are not entirely obsolete, e.g.https://www.mouser.com/c/optoelectronics/led-lighting/led-emitters/standard-leds-through-hole/?q=bipolar%20LED&instock=yI've not tested it but I would think such a bipolar LED running straight off 240VAC with just a resistor would flicker less than a neon, as the LED conducts and makes some light nearly to the zero crossing, whereas the neon cuts out entirely by something like 40-50V, EDIT: and doesn't light again until the voltage raises to the strike voltage of something like 80-90V.

author: rfclown
author_rank: Frequent Contributor
timestamp: October 22, 2021, 07:02:08 pm
content: Quote from: Benta on October 22, 2021, 06:26:41 pmI would think it would be highly dependent on the LED. The ones I'm using emit some light with very little current. I put 3V DC across the circuit and I still see some light. I have LEDs in my junk bin at home from when I was a teen in the 1970's which would probably have barely perceivable light with 1mA and would certainly flicker. There's no reason to use LEDs like that anymore. I'll try looking at it in the dark to see if I can notice flickering. I'm actually at work now and I had it laying on a workbench in a brightly lit room.

author: floobydust
author_rank: Super Contributor
timestamp: October 22, 2021, 07:09:11 pm
content: A neon lamp on mains does flash, each electrode (cathode) lit on alternating 1/2 cycles. youtube vid high speed camera 1,000fps in slow motion showing that.LED nightlight, typically 100R 1/4W surge resistor with 1uF and 120VAC, commercial products use carbon resistors but I wasn't comfortable with their flammability.I changed to 1/4W fusible and it works... until... if you switch on at a mains peak it fused. Such a hassle.

author: james_s
author_rank: Super Contributor
timestamp: October 22, 2021, 07:28:44 pm
content: Neons do flicker, but to my eye it is not nearly as visible as it is with LEDs, probably down to the fact that most are single die and used without a bridge rectifier. Either way it doesn't take much capacitance to fix that.Carbon resistors will typically burn out without actually setting anything on fire. Especially if they are heavily overloaded they just pop.Side note about neons, if you run them from DC only the cathode will illuminate, and lifespan is significantly reduced.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 22, 2021, 09:33:11 pm
content: Quote from: Benta on October 22, 2021, 06:26:41 pmI definitely can see it (100Hz flicker). I have to look really hard in the daytime to see it but I can just about. However in the dark I can see it flicker clear as anything!

author: james_s
author_rank: Super Contributor
timestamp: October 22, 2021, 10:19:35 pm
content: 100 Hz flicker is very, very obvious to me, it's something that really jumped out when I visited England. Part of that is the lower frequency and part of that is probably that I'm used to 120 Hz flicker, it got less noticeable after a day or two but motors and transformers still all sounded weird to me. My friend from there is over here somewhat regularly for business and has said the same thing about the motors and transformers here sounding weird.I can see flicker at much higher frequencies than that though, 300-400 Hz PWM backlight flicker gives me a headache and I can see it in my peripheral vision, especially if I'm tired. The 1 kHz flicker of Philips Hue lamps is visible any time I move my head or eyes, that took some getting used to at first, now I can mostly tune it out. The PWM flicker of many car tail lights is very visible to me too, again largely down to motion. When people say that the human eye cannot perceive flicker above x frequency they are ignoring the fact that a person is rarely sitting still just staring into a light source. The moment you move your eyeballs to look at something you turn a flickering light into a dotted line and that strobe effect is readily visible well into the kHz range.

author: StillTrying
author_rank: Super Contributor
timestamp: October 23, 2021, 12:17:02 am
content: Some of us must have fast eyes,I can easily see 50Hz & 100Hz flicker, and the 25 frames per second of a TV picture even though the backlight doesn't flickerI sometimes wonder how lip readers manage off a TV screen.

author: james_s
author_rank: Super Contributor
timestamp: October 23, 2021, 01:03:22 am
content: Many modern TVs do have backlights that flicker, it is synchronized to the video frame rate.The first time I ever saw a PAL-50 CRT TV was about 20 years ago when I was involved in the original Xbox game console. We had a TV shipped over from Germany to test something and the flicker looked so bad I couldn't see how anyone could watch it. I suppose you get used to it after a while and don't even notice anymore.

author: rfclown
author_rank: Frequent Contributor
timestamp: October 23, 2021, 01:31:09 am
content: So I compared a neon with the LEDs that I wired with a resistor. The neon had a 68k soldered to the lead. My back-to-back LEDs have 47k x 2=96k. I looked at them in the dark. LEDs are WAY brighter than neon. My 60 year old eyes don't see flicker. I tried looking in my peripheral vision. Don't see flicker. If I move me head back and forth I can't see flicker. If I wave them back and forth rapidly I can distinctly see the stobe effect. The on/off duty cycle of the neon and LEDs seem similar. So for the OP's problem, I don't see anything more necessary than back-to-back LEDs with a resistor. If some some people notice the flicker (which is obviously true based on this post) then I wouldn't think it needs be any worse with LEDs over neon (as long as appropriate LEDs are chosen). With a large series resistor there isn't any of the problems associated with capacitor/recitifier method. I wondered if the LEDs would excite glow-in-the-dark phosphor, so I put them behind a glow-in-the-dark star that was on the ceiling in the kids room. No luck. I thought that might me a good way to smooth out flicker. Maybe with the right color LED and the right phosphor? One of my LEDs is white and the other is yellowish.

author: Vovk_Z
author_rank: Super Contributor
timestamp: October 23, 2021, 09:37:54 pm
content: Quote from: rfclown on October 23, 2021, 01:31:09 amI told about this in Reply #41.

author: Benta
author_rank: Super Contributor
timestamp: October 23, 2021, 09:51:55 pm
content: Quote from: rfclown on October 23, 2021, 01:31:09 amThe OP doesn't have a problem, it's just about playing around and learning things.Quote from: rfclown on October 23, 2021, 01:31:09 amWhite LEDs already have a phosphor layer. The chip is mostly blue in cheap devices and excites a yellow(ish) semi-transparent phosphor. To do this, the exciter wavelenght has to be shorter than the phosphor wavelength (=higher energy), so your experiments were futile.More advanced LED technologies use UV chips, which gives more possibilities on phosphor mix and thus better color rendering.

author: tooki
author_rank: Super Contributor
timestamp: October 24, 2021, 12:48:12 am
content: Quote from: james_s on October 23, 2021, 01:03:22 amIt was a big enough problem for enough people that high-end PAL TVs doubled the frame rate to 100Hz, presumably using some form of buffers to show each frame twice. That must have been quite a technical achievement before the days of digital video! Later ones used digital buffers, and Philips even made some that were actually 75Hz TVs using motion interpolation similar to what modern TVs use.

author: tooki
author_rank: Super Contributor
timestamp: October 24, 2021, 12:53:56 am
content: Quote from: Benta on October 23, 2021, 09:51:55 pmDo you know of any examples of UV-based LEDs in the wild? I’ve heard of them as a theoretical, but have never found one actually on sale. And given how inefficient UV LEDs still are, it comes as no surprise that blue is the foundation for modern LED illumination. Certainly the high-CRI white LEDs are not UV-based; you can get high-CRI remote phosphor panels, and they’re designed for blue LEDs.

author: Zero999
author_rank: Super Contributor
timestamp: October 24, 2021, 08:52:21 am
content: Quote from: Benta on October 23, 2021, 09:51:55 pmMost glow in the dark phosphors are green and can be excited with blue light. I've not had any problems with glow in the dark stuff not glowing, when exposed to LED lights. I discovered this back in the 90s, when I got hold of some of blue LEDs, when they first became available, albeit very expensive.Quote from: tooki on October 24, 2021, 12:53:56 amI don't know of any, but it's often not specified. I suppose the advantage of using UV is the phosphor's emission becomes more dominant.Modern deep violet/near UV LEDs are very efficient, perhaps often more so than blue. This data sheet gives an efficiency of 61.7% for 385nm and 395nm LEDs, vs 57% for blue 450nm.https://www.mouser.co.uk/datasheet/2/810/NewEnergy_StarBoard_Horticulture_Luminus_DataSheet-2509530.pdfOn the other hand, the higher the energy of the radiation exciting the phosphor, the greater the Stokes shift losses, so UV would be a net loss, efficiency-wise.

author: tooki
author_rank: Super Contributor
timestamp: October 24, 2021, 04:57:22 pm
content: Quote from: Zero999 on October 24, 2021, 08:52:21 amNo, but the forward voltage is specified, and it seems to always match that of blue LEDs. The Vf of UV LEDs rises dramatically with wavelength. A true UV-A emitter from a respectable source (e.g. Osram) has a single-die Vf of 4V (±0.5V), and UV-B and -C LEDs from 5V to upward of 7V!Even just the ~400nm near-UV LEDs have noticeably higher Vfs than blue LEDs.I just took a look on Digi-Key, and there is exactly one line of white LEDs containing models whose Vf is high enough (and the drawing explicitly showing it having just a single die, not multiple in series) that I thought it had to be real UV: the Lumex Titanbrite line, whose 5W (SML-LXL99UWC) and 3W (SML-LXL8047) models have a Vf of 4.5-4.6V. The 405nm near-UV version of the SML-LXL8047 line has a Vf of just 3.6V. But the blue (454-465nm) versions of both models also have exactly the same 4.5-4.6V Vf, so I guess they, too, are blue-based.Hence my skepticism thatanyUV-based phosphor-converted LEDs are actually on the market.

author: james_s
author_rank: Super Contributor
timestamp: October 24, 2021, 07:37:20 pm
content: I'm reminded of a curious effect I noticed some time back when I first built a violet laser pointer after HD-DVD lost the format war and pickup units became available cheaply. In my house the cover plates on the outlets and switches are made of a hard white plastic and when excited by the violet laser it fluoresces light greenish. It even has some persistence, if I sweep the beam across a switch plate it will leave a green trail that fades out over a second or so. I have no idea why those plates fluoresce, they are not glow in the dark. Maybe it's part of the dye that makes them white? I don't know.

author: rfclown
author_rank: Frequent Contributor
timestamp: October 24, 2021, 08:05:45 pm
content: Quote from: Zero999 on October 24, 2021, 08:52:21 amPut a blue LED behind a glow in the dark star (greenish) and sure enough there was some persistance.