LED candle bulbs

[Colin Stamp]

Hi all,

I tried out some Ikea LED candle bulbs today, wondering if 90 lumens would be enough:-

I thought I was impressed. 90 lumens turned out to be a little bit on the dim side, but they look quite reasonable in the fittings, which were intended for halogen candles. The light comes out in about the right places IYSWIM, The colour is fine and they're cheap.

Then came the realization. The sodding things strobe really badly. Now I've noticed it, I can't get away from it. Anything that moves in the room turns into bloody set of freeze-frames, as does the whole room every time you move your eyes!

Is this a common thing with cheap LED bulbs? I'm all worried about the impending Ebay purchase of Chinese replacements now. The only other LED bulbs I've got are two brands of GU10 and they're fine, so maybe it's just Ikea ones that are crap...

Cheers,

Colin.

[Andy Champ]

I've seen this in an hotel, which had a row of LED spots. My son has bought LED throughout for his house, and they don't strobe at all - and they were off-the-net cheapies AFAIK.

Andy

[Brian Gaff]

Well the issue of course is that they have no thermal persistence as most of the filament bulbs do and presumably go out completely when zero is crossed. I'd have thought in this day and age they would have been able to sort this out electronically, though of course if they did use a switch mode solution the crud put out in the RF area might be rather bad.

Brian

[Brian Gaff]

Hmm, so what makes leds have an issue with higher frequencies then, I'd have thought this was of no concequence , but maybe its to do with the individual colours of led in the package having different levels on higher frequencies.

Brian

[The Natural Philosopher]

They are so bad that they are de facto light source for infrared remote controllers operating at tens or hundreds of khz..and for driving optical fibres at GHZ rates.

Man, that's really bad. .

[Terry Fields]

At the end of last summer I replaced every halogen and CFL in the house (bar 4) with LED. After some disappointments with ebay offerings I chose to go with a premium make, Philips in this case. Although I can easily sense it, none of these appear to strobe. I find modern car LED lighting to be irritating, for example.

The only 4 that I can't replace are two 20W CFLs (no single LED is yet available at the lumen level) and two G9s where only a halogen is small enough for the fitting (bathroom and ensuite).

With our lighting usage pattern I estimate these will have paid for themselves in two years, with the expectation that over their 15000 - 30000 hour lives they will be massively cheaper to run than halogens or CFL

[Tim Watts]

On Wednesday 27 February 2013 09:19 Brian Gaff wrote in uk.d-i-y:

I've driven LEDs (very high brightness types but not full on mental Cree types) at upto about 10kHz with no apparantly ill effects. At that frequency there will be no strobe effects that a human could detect.

[Tim+]

This might be because they're coated with some sort of "phosphor" to produce a warm white light. Certainly all the LED spots in my kitchen glow for a few seconds after switch-off. They could be strobing under the coating.

Tim

[Colin Stamp]

I've noticed that on some of my bulbs too and I thought it was down to phosphor after-glow too, but I've since played with individual LEDs and found that they go out instantly and completely if they're disconnected from the driver. An impressively small current will make them glow enough to be seen in the dark and some drivers do manage so store enough charge to make it happen for a few seconds.

Cheers,

Colin.

[Colin Stamp]

Sounds comforting. I think I'll chance it...

Cheers,

Colin.

[Tim+]

Could be that but my kitchen LEDs do seem to have something painted over the top to generate a warmer light.

Tim

[Andy Champ]

Certainly not warm white - 6000K.

Andy

[docholliday93]

It's a long while since I was using LEDs to drive optical fibre links, but I recall that they ran out of steam at around 10MHz for most types, with so me specialized ones managing up to 100MHz. Almost all the links I've looked at since (and everything at above 100 Mbit/s) use lasers, and a high propo rtion of those use a separate (even if possibly integrated in the same pack age) modulator. Visible LEDs as I recall were something like an order of magnitude slower t han infra-red - but I'd agree that this is still more than fast enough not to be visible.

[Tim Streater]

I have this recollection that the short range optic modules for Juniper routers (over multi-mode fibre) used IR LEDs at 850 nm. These would be driven at any speed up to 10Gbps. The longer range modules (up to 60km or so of single-mode fibre) were all lasers at 1310 or 1550 nm.

[docholliday93]

Are you sure they were LEDs? I'd have expected them to be VCSELs (vertical cavity surface emitting lasers); I've seen a lot of gigabit ethernet modules for short distances that use 850nm VCSELs. Mike

[Colin Stamp]

They are usually switch mode. The ones I've seen run at a few tens of kHz, but there is still the 100Hz pulsing of the rectified mains supply to contend with. If it isn't smoothed before driving the switcher, then the switcher will die and restart every half-cycle. It only takes a capacitor to bridge the gaps, but it seems Ikea saved some money...

Cheers,

Colin.

[D.M.Chapman]

Yep, the cisco optics I was spec'ing today were 850nm for short range,

1550nm for the 40km ones.

Eye watering prices...

Darren

[Tim Streater]

Well quite :-)

But upthread there seemed to be an assertion that you couldn't drive LEDs at the sort of frequencies I mentioned. So I'm not sure whether that's just wrong or that I missed something ...

[D.M.Chapman]

Ah, no idea what's in them. Something very valuable (or maybe that's the special expensive Cisco sticker)

are the things I've been using. DS-SFP-FC8G-ER to be precise. No clue on that page that I can see as to what they actually are...

Darren

[Tim Streater]

I think the sticker on them should warn you that's it's a laser device. I can't remember if the short-range ones actually say LED on them or merely that they *don't* say laser.