Two LEDs which seem similar, but are totally different in PF - but why? - Page 1
Forum section: electronics / projects

author: PushUp
author_rank: Regular Contributor
timestamp: August 29, 2024, 09:27:43 pm
content: Two OSRAM LEDs with 2700K and 2452lm, but totally different in consumption, PowerFactor and therefore sine wave - but why?!When I bought these LED lamps some time ago, I only looked at the front and side of the packaging, but not at the ingraved writing showing the real consumption in mA, which is obviously the decisive factor, because other than that, one could think that there cannot be something totally different between "Superstar and Star"..., because looking at "Superstar with 20W" and "Star with 19W" you are already fooled, when you think this is the truth...LED Superstar Classic A 150 (Dimmable) vs. LED Star Classic A 150When I checked them later, in order to compare them with other manufacturer, I was surprised about the consumption, which, however, is ingaved in light grey on each lamp - but very small and not readable at a certain age without reading glasses...Therefore, I was curious, why there is such a big difference between both models, allthough the main values printed on the packaging are equal?!Superstar: Due to my chosen conversion of the clamp A is mA and you can forget the "k" in front of the ernergy table...Star: Due to my chosen conversion of the clamp A is mA and you can forget the "k" in front of the ernergy table...Does anybody know or has an idea, why the "Superstar" has such a good PF of 0,93 and therefore a better "destorted sine curve", than the "Star" with a bad PF of 0,60 and therefore a "totally destorted graph"? Is it a better construction or due to the usage of better components, more filtering?The next question is, when it is possible to build LED lamps with quite a good PF of 0,93, why is it not committed to always build these lamps in order to save energy, save the environment and prevent your installation of getting a more and more hotter neutral conductor?Yes, the truth will probably be - as usual - corrupted politicians, lobbyism, manufacturer beeing dead keen on money to please the stock market speculator and so on...When I went to school, I often saw cars with stickers ending with the sentence "...and than you realize, that you cannot eat money!" Funny enough, the knowledge is there, but we haven't learned anything, but being more selfish than anytime before...Nevertheless, when the lamps are dead I will open them and post some pictures, as I am probably not able to reverse engineer them, but maybe some other has opened some similar LEDs before and know the answer?!Cheers!

author: tunk
author_rank: Super Contributor
timestamp: August 29, 2024, 09:37:59 pm
content: Maybe this can shed some light on it, i.e. linear driver and step down switcher:https://goughlui.com/2024/08/25/teardown-luce-bella-led-globes-6w-470lm-8w-806lm-a60-15w-1400lm-par38/

author: coppice
author_rank: Super Contributor
timestamp: August 29, 2024, 09:51:56 pm
content: Other that the packaging and output, how are these two bulbs similar? One is dimmable, and one isn't. That is huge. I assume the dimmable one was considerably more expensive. They usually are. They are usually rather more complex, leading to that higher cost. You can get away with some shortcuts in a non-dimmable bulb, but you need to do things properly to make LED lamps dimmable with a wide range of dimmers. A few years ago this was quite a research topic amongst LED lamp makers. If you went into their labs they had collections of every commercial light dimmer they could lay their hands one, and they tested bulb designs against every one of them. The consumption of these lamps is below the threshold where regulations require any power factor correction.

author: CaptDon
author_rank: Super Contributor
timestamp: August 30, 2024, 01:57:15 pm
content: I have a triac dimmer in my range hood over the stove and I get different results among different manufacturers of dimmable LED bulbs. Differences even among the same manufacturer when bought years apart. And to the O.P., you compared dimmable to non-dimmable and then wonder why the difference? Why does an apple taste different when compared to a pear? Some of the original non-dimmable LED bulbs were total shit using a series capacitor as the current control and a very small low value resistor which would basically explode when the LED or bridge rectifier shorted. These bulbs would blow out instantly when the mains got hammered with a spike like motor turn-off or nearby lightning strikes. And the series capacitor indeed gave them a very very poor power factor. The VA vs. true power was about 2:1.

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 30, 2024, 03:06:02 pm
content: Quote from: PushUp on August 29, 2024, 09:27:43 pmWhat now?The waveforms of the undimmable LED are what you'd expect for a simple bridge rectifier and a flyback or even buck converter. To make a LED dimmable, you're looking at spending a few more .01$ on the switcher IC, chances are due to topology and market segment the PF comes almost for free once you are shopping on the no-bottom-of-the-pile.Also, 99.9% of non-industrial customers won't notice a low PF. Not in appearance and not on their bill.

author: coppice
author_rank: Super Contributor
timestamp: August 30, 2024, 03:21:00 pm
content: Quote from: CaptDon on August 30, 2024, 01:57:15 pmA "dimmable" LED bulb doesn't mean it works well as a dimmable bulb. It mostly means they haven't done things like use an RC supply, that catches fire with the seriously distorted waveforms from most dimmers. You can expect some dimmability, but the range is often quite narrow.

author: Marco
author_rank: Super Contributor
timestamp: August 30, 2024, 04:33:32 pm
content: Oh come now, good bulbs dim quite well.They would have done better if the market had simply decided to have 90 degree phase angle be 0 intensity for trailing edge. Would have made the electronics so much easier.

author: coppice
author_rank: Super Contributor
timestamp: August 30, 2024, 04:59:10 pm
content: Quote from: Marco on August 30, 2024, 04:33:32 pmYes, some LED lamps do dim well. As I said earlier, a lot of work went into ensuring they do. The range of dimmer architectures is quite large, even if a high percentage are a simple triac design, and good lamps will give a reasonable brightness range with most of them, without going into unpleasant flickery modes. However, the label "dimmable" on a lamp can't be trusted to mean much more than it has a low probability of catching fire, and offers at least a little variability.

author: Marco
author_rank: Super Contributor
timestamp: August 30, 2024, 08:41:02 pm
content: Some bulbs just say they work only with trailing edge, but needing to support phase angles less than 90 degrees still needlessly complicates matters.The LED industry should have just said "screw the legacy for trailing edge, that's ours now".