Flickering led floodlights

John D v2.0 · 18 Nov 2019

Hi all
Yesterday i bought an led work light from Lidl which generally seems excellent quality. It's got 2x30w floodlight on top and plugs into a normal socket. It's some Lidl own make https://www.lidl.co.uk/en/p/diy-tools/parkside-2-in-1-twin-30w-led-work-light/p27220

However i noticed a weird effect when i was using it and eventually realised it's flickering at a high frequency.

If I wobble a tube of caulk with nozzle in front of a Phillips bayonet led light or a fluorescent tube work light it looks like a blur, but in front of the work light i can see several separate nozzles.

Is this normal for led lights or is this grounds for a refund? I can't imagine Lidl staff having any idea!

EFLImpudence · 18 Nov 2019

That's how they work.

Don't use it when wobbling your nozzle or using rotating machines.

I'm surprised you haven't seen it discussed on here.

bernardgreen · 18 Nov 2019

EFLImpudence said:
That's how they work.

To make the light appear brighter many LED lamps over drive the element with pulses of current that are several times the rated continuous current, The average current is less than the rated current but the apparent brightness is significantly more than it would be is run at the maximum rated continuous current

^woody^ · 18 Nov 2019

I thought all bulbs actually flicker to some extent, and that is why you should not use flourescents for things like grinding or machining as the machine could appear stationary, but with incandescents we can't perceive it as the filament retains some glow between flickers.

John D v2.0 · 18 Nov 2019

Thanks for the replies.
Just to be clear i have a fluorescent tube on a stand and a normal led bayonet bulb which i usually use for diy and they don't have any perceptible flicker. So this isn't something fundamental.
So I'm wondering if it's something to do with buying a Lidl light or is that par for the course if you're not paying a lot for Phillips warm white frosted bulbs.

John D v2.0 · 18 Nov 2019

EFLImpudence said:
Don't use it when wobbling your nozzle or using rotating machines.

That sounds like a good argument that it's not fit for purpose! Generally i don't play musical statues or move like a cat burglar when doing DIY.
The nozzle test was just to check what was going on with the flicker.

I probably have seen it discussed on here but nowadays i don't read most of the threads exhaustively. If anyone has a recommended light then I'd love to hear.

ericmark · 18 Nov 2019

If sold as flood lights, then one can expect a 50/100 Hz strobe effect as with any fluorescent light with wire wound ballast, but when sold as "work" lights, then unless a warning in included, then I would say you can expect a frequency high enough not to freeze motion.

If in the 1980's we bought a work light using a fluorescent tube, we would expect the 100 Hz output, but as the wire wound ballast has been replaced with electronic versions, we expect the lights to be strobe effect free. So where in 1980's we would expect the lamp to be marked if it can be used with rotating machinery, today the reverse is true, we expect it to be marked "don't use with rotating machinery" as with an electronic ballast or a LED driver in the main the frequency is too high for there to be a problem.

Jackrae · 18 Nov 2019

With your head and eyes absolutely still do you see the flicker - if you do then the light may be faulty
If you only see the flicker when you move either your head or eyes then what you observe is the pulsed light as previously stated.
This effect can often be seen on road works yellow hazard lamps whilst driving in the dark.

John D v2.0 · 18 Nov 2019

Jackrae said:
With your head and eyes absolutely still do you see the flicker

No can't see it until something moves,eg if you move your hand reasonably quickly or drop something.
I have worked out the manufacturer and will email them later. They are a Benelux company.

Jackrae · 18 Nov 2019

That basically proves the LEDs are pulsed and the effect you observe is perfectly 'normal'

John D v2.0 · 18 Nov 2019

apparently not all do it - the osram ones are apparently better https://www.ledinside.com/lighting/...ove_video_recordings_at_skate_park_in_germany

Jackrae · 18 Nov 2019

Bet they didn't pay Lidl prices though

John D v2.0 · 18 Nov 2019

you may bet, but to be fair to osram, they are lidl prices pretty much - I just bought a couple from cpc farnell for 16.20 each, to replace the ones on the Lidl fixture. https://cpc.farnell.com/ledvance/4058075097483/floodlight-20w-4000k-black-ip65/dp/LA07577
CRI 80 rather than 65 too, significantly better efficiency (2100lm from 20w rather than 2400lm from 30w)

Lidl fittings can go on the side of the house I suppose, that's about all they're good for.

SimonH2 · 19 Nov 2019

Many (most ?) non-dimmable LEDs simply put the LED emitter across the mains with some form of current limiting impedance and bridge rectifier. Result is that you get 100 pulses of light/second and periods of zero output in-between. There may be some persistence from the phosphor used to convert blue to white, but this seems to be minimal.
Flouro tubes with magnetic ballast do the same, except that there is more scope for smoothing from the phosphor used to convert the UV generated by the internal discharge into light. Flouros with HF ballast will still do it, but at a higher frequency - and the phosphor will do a better job at smoothing the output at the higher frequency.
I do remember in school physics, the teacher demonstrated with light sensor and oscilloscope the pulsing even from an incandescent bulb with it's high thermal mass.
In a workshop with 3 phase supplies, it is good practice to split the lights between phases - that way, the gaps in output from one phase will be hidden by light from the other phases.

John D v2.0 · 19 Nov 2019

new floodlights (CRI80 and low flicker) should be arriving tomorrow some time, I will report back with my findings.

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Flickering led floodlights

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