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Thread: LED Bulb questions

  1. #17
    Senior Member AGTDenton's Avatar
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    Re: LED Bulb questions

    Quote Originally Posted by cptwhite_uk View Post
    my main lights in various rooms in the house are 20W Philips LED - equivalent to 120W incandescent if I remember correctly - the colour is pleasing, bright, and it's still working exactly as it was at the point of install 6 years ago.
    I find the 6W bright enough. I must have horrendous eyes
    I set myself a target of no more than 6

    There was an incandescent 120W bulb when I moved into my previous place, was as strong as looking at the sun.

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  3. #18
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    Re: LED Bulb questions

    Quote Originally Posted by spacein_vader View Post
    I've got a couple of rooms with dimmers in, I've found that all LED bulbs sold as dimmable work But you have to invest in a decent brand "trailing edge" dimmer switch.

    ...
    I shouldperhaps have clarified. The "expensive dimmer" wa an old (c.1988) dual-gang dimmer for incandescents. But it was working rather weirdly. As I dimmed, ower usage dropped (as expected) up to a point but then went up. Worse though, if I clicked it to turn it the lights (two 60w incandescents per gang) it somwhow drew more power turned off than on, but low. So, it was drawing about 10w per bulb, 24/7 even while lights were "off". Something was well screwed in there. A replacement switch was about £50 in those days, so I replaced the dimmer with simle dual-gang on/off, and put in wifi bulbs with a remote each for me and wife. When they finally pack up, I guess smart bulbs will go in, instead, not least 'cos they seem to have killed off the market for the other type utterly.

    @cpt_white .... What my appear to be doing, logically if not physically, is that there seem to be 10 'dim' levels. It seems like there are 10 banks of LEDs, and if you dim by one level, one bank switches off.

    I'm no LED expert, but I've never seen an LED that could 'dim' so sure, I guess it either has to be a rapidly switching on-off and the timing of the off bit lengthens as you dim, but I'd have thought that was likely to result in flicker. Or, it's using that "10 banks" principle, nd dimming just turns more banks off, but the ones that are on are on all the time.

    Turning LED bulbs off seems to result in a tiny level of continuous power draw. I assume something has to be monitoring a wifi circuit for the 'on' signal, but it's nowhere near the rather substantial draw that antique '80s dimmer used when it should have been using 0.0W. Turning my smart LEDs off at the wall switch (as opposed to via wifi) and they do consume zero power, as I would expect.

    But that tiny power draw, 24/7 if wifi is enabled, is one reason (the other being standard LEDs are far cheaper than smart ones) that I have way more non-smart than smart. Also, of course, unlike smart bulbs, nobody can data track when bulbs are on or off if they are dumb bulbs with a physical switch.

    The data aspect of smart bulbs does concern me a bit (it being a personal hobby horse) but, it's one of those areas where privacy comes second (for me) to functionality. In many ways, I'd still rather have the little remotes than use a smartphone/Alexa for lighting but, I just can't get the goods ones (and haven't been able to for several years now).
    A lesson learned from PeterB about dignity in adversity, so Peter, In Memorium, "Onwards and Upwards".

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  5. #19
    root Member DanceswithUnix's Avatar
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    Re: LED Bulb questions

    Quote Originally Posted by Saracen999 View Post
    I'm no LED expert, but I've never seen an LED that could 'dim' so sure, I guess it either has to be a rapidly switching on-off and the timing of the off bit lengthens as you dim, but I'd have thought that was likely to result in flicker. Or, it's using that "10 banks" principle, nd dimming just turns more banks off, but the ones that are on are on all the time.
    Oh dimming can be done, but it involves some pretty nasty analogue current control which would be tricky to implement and would generate heat which is the enemy in things like LED bulbs.

    Instant on really is instant with LEDs, down in the microsecond region easily. So if you want to dim an LED you just PWM drive it, usually at about 1KHz so way above the 60Hz that people can see as a flicker. So 10% brightness will have the LED on for 0.1ms and off for 0,9ms. You can do that easily with a microcontroller (cheap) and power switching FET (cheap), which usually have a hardware timer circuit where even a cheap 8 bit timer can do 256 level PWM. Those 256 levels will be far from linear to the eye, so there might well be a 10 entry table to map perceived brightness to PWM values.

    It seems odd that digital electronics has got to the point where the cheapest and best way to drive an LED is to give it more computing power by far than the first desktop computer I had (a TRS-80 clone with 1.79MHz Z80) but that is where we have been for many years now.


    The WiFi LED bulbs, they will contain an ESP32 chip to monitor the WiFi or Bluetooth. Those have to be always running, and are a 32 bit dual core 160MHz or faster 32 bit controller. I used to play Quake on something slower than that, but complete with the radio circuitry they are about a quid.

    https://www.aliexpress.com/item/32826540261.html
    Last edited by DanceswithUnix; 27-01-2022 at 08:32 AM.

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  7. #20
    Senior Member cptwhite_uk's Avatar
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    Re: LED Bulb questions

    I'm guessing the stepping in brightness Saracen appears to perceive, is more likely due to stepping of the digital signal for the time on/off cycles, which is being interpreted as a single LED cell switching off as you adjust the dimmer. That would probably make sense.

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    Re: LED Bulb questions

    Interesting, DwU. Very. That all makes sense. I guess I'd never really given it much thought especially into the relationship between how fast we can get the electronics to drive LED switching, compared to our eye (or brain) to perceive it. But ultimately it's the same trick as everything from a pack of cartoon 'cards' to running still video framestoo fast for us to detect it, leaving the mental impression of motion when there isn't really.

    As for "dimming", it seems the issue is one of definition.

    Are those individual LEDs 'dimming' in the snse that lower power into an incandscent dims? As I understand it, no. They're either on or off. owt in-between.

    But .... if you look at that LED 'bulb' (which really isn't a good description of it) as a system, then the output of that system as a whole, rather than individual LEDs, then that light output cold 'dim'.

    An analogy might be my lounge. Two ceiling light fittings, each with two 'bulbs', and a few wall lights. With incandescent bulbs, I used go vary the light output of a single bulb's filament by varying the dimmer. The light in the system, i.e. the lounge, went up and down. I could somewhat do the same thing with incandesants without a dimmer by switching individual filaments on and off, varying the light level in the lounge as a whole.

    And if I could have switched those incandesnts on and off fast enough I could have varied the overall effect much like an LED bulb does. In theory. In practice, of course, it's a total non-starter not only 'cos no way could I switch them all anywhere near fast enough, but the sheer physics of heating and cooling the filaments couldn't be done that fast. Or anything near.

    TRS-80? That takes me back. I never owned one but I used one (well, two, IIRC) at work a fair bit. Genuine Tandy ones not clones, and again IIRC, a Mk.3 then a Mk.4. Other than a TI 'programmable' calculator (which was pretty damn sophiticated for the early '70's) my first actual computer was an Apple II (Europlus), which was a 6502. But .... I had an optional plug-in board with a Z80 chip on it, because I wanted to run CP/M for a project.

    When I think of how sophisticated that as for those days (late 70's, early 80's) .... most people could probably barely spell 'computer' never mind have one at home) andd you then compare to the power of modern computers .... I mean, it's mind-boggling how much we could do even then, then you scale up to modern graphics, even 'just' for games, voice recognitionneeding just a phone or smart speaker, end to end encryption, medical advances, materials technology .... and so on. I mean, here's me thinking about a £400 3D printer (Prusa Mini Plus) and what it can do, and it's FAR from the cheapest 3D printer out there and I'm years late to that party, yet it's capability could have been sheer sci-fi back in the '70s.

    All in barely 50 years.

    What will the world look like in another 50? Or 500? If we haven't blown ourselves to kingdom come in the meantime.

    I remember, a few years ago now, visiting Thomas Edison's home in Key West, and seeing what (according to claims) were some of his original hand-made incandescent bulbs still working (never switched off or on apparently, and running pretty low power). Before that, no electrical lighting. And now compare that to the nature of the LED 'bulbs' we are talking about here.

    We live in interesting (and fast-moving) times.
    A lesson learned from PeterB about dignity in adversity, so Peter, In Memorium, "Onwards and Upwards".

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  11. #22
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    Re: LED Bulb questions

    Quote Originally Posted by Saracen999 View Post
    Interesting, DwU. Very. That all makes sense. I guess I'd never really given it much thought especially into the relationship between how fast we can get the electronics to drive LED switching, compared to our eye (or brain) to perceive it. But ultimately it's the same trick as everything from a pack of cartoon 'cards' to running still video framestoo fast for us to detect it, leaving the mental impression of motion when there isn't really.

    As for "dimming", it seems the issue is one of definition.

    Are those individual LEDs 'dimming' in the snse that lower power into an incandscent dims? As I understand it, no. They're either on or off. owt in-between.

    But .... if you look at that LED 'bulb' (which really isn't a good description of it) as a system, then the output of that system as a whole, rather than individual LEDs, then that light output cold 'dim'.
    A conventional dimmer should switch on both halves of a mains cycle, so 100 times per second for us. That gets smoothed out by the thermal inertia of the strip of tungsten in a filament bulb, but will still be a rapidly changing light level so also partly by our eyes (specially if it is a halogen bulb).

    But essentially, yes I would say the LED is dimmed. The number of photons hitting your eye in a given millisecond will be the same whether you are looking at a slightly colder than expected strip of tungsten or a pulse width modulated LED. Walks like a duck, quacks like a duck...

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    Re: LED Bulb questions

    Got a pair of these for a 4 spot Chandelier unit to replace 4 old candle incadescents:
    https://www.amazon.co.uk/gp/product/B08K3BLL5Y/

    Very bright!

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    Re: LED Bulb questions

    I'm trying to do the same at home here, as bulbs go I'm looking to replace them with LED bulbs. The annoying this is that the previous owner of our house had fitted halogens in the majority of the rooms. Thus far I've found the LED bulbs we want to use aren't happy with the supplied and fitted transformer for the halogens. Our electrician can't find all the transformers either as they have been stuff in the ceiling in such a way we will have to make large holes.

    We're using 6 watt ones I think and they are nice and bright. Looking forward to getting rid of my florescent strip lights I've got here in the garage not only do they give me a head ache I don't think they are very cheap to run.

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    Re: LED Bulb questions

    I have replaced all my bulbs with LED equivalents from Screwfix, inside and outside. Most have lasted 3 plus years and very happy with them. Clas Olsen still open in Reading last Thursday.

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    Re: LED Bulb questions

    I'm a bit late to the thread but in case it's still useful, I find the Diall branded ones from B&Q decent, I generally get the 10.5W ones. I've tried a few brands (including some big names) and am yet to find anything consistently better overall. YMMV, naturally.

    I'm very sensitive to the stroboscopic effect you get from cheap bulbs but have never detected it with this brand. Colour temperature/CRI are also decent enough from the ones I've used.

    The output angle, while I forget the exact number, seems decent too - many brands seem to be limited to about 180 degrees which leaves a dark patch above them on the ceiling which makes the whole room look gloomy.

    I also got a multipack of 11W Philips ones from Amazon which are generally fine, but a few out of the pack have a noticeable buzz/hum, some worse than others. I didn't notice beforehand but a few reviews on Amazon mention it too, so it's not just me. Not really an issue for use in e.g. the bathroom, but can be annoying in quiet rooms.

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  20. #27
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    Re: LED Bulb questions

    Quote Originally Posted by Saracen999 View Post
    I remember, a few years ago now, visiting Thomas Edison's home in Key West, and seeing what (according to claims) were some of his original hand-made incandescent bulbs still working (never switched off or on apparently, and running pretty low power). Before that, no electrical lighting. And now compare that to the nature of the LED 'bulbs' we are talking about here.
    I'm not sure if it's what you meant, but electric lighting existed long before Edison commercialised a product, largely building on Joseph Swan's design. Humphrey Davey's arc lamps existed from the early 1800's, and the fluorescent lamps from the mid 1800's.

    The incandescent lamp most of us know was a very different design again, a tungsten filament design by Just and Hanaman, produced by Tungsram (later Osram).

    And many other types and iterations of lighting in between and since, with credit due to a lot of people, including the Nobel-prize winning invention of the blue LED (allowing the production of white LEDs) by Isamu Akasaki. It's an area where the perception of the history is quite far removed from the actual history, and one name in particular seems to get a lot more credit than his fair share.

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