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Twin Tube HF fluorescent lighting for the workshop

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Adam Harris11/10/2018 21:22:06
470 forum posts
26 photos

Despite the original intent of going LED for workshop lighting (garage 2.5m wide x 7m long) I ended up this week buying five 6' Twin HF 70w Flourescent lamps (Viper from LCD Direct) which do not have the dangerous stroboscopic effect on moving machinery. Only so far wired up 2 in series to one on/off switch , and after 5 seconds of light the mains board RCD trips out (it is a 63A 230V RCCD that trips at 30mA). I have now learnt the expensive way that fluorescent and RCD's are not easily friends! Is there something to be done to cure this problem or should I try to return them? Would it make a difference to have a separate on/off switch for each light and start them each in sequence separately? Is the overall running leakage on total ten 70w tubes simply incompatible with a 30mA current trip RCD? Any suggestions from those using these twin HF lights? Thanks for any help

Andrew Tinsley11/10/2018 21:29:17
1170 forum posts

I have always used ordinary fluorescent tubes plus chokes and I have never had any stroboscopic effects! Even if you did, the racket that any machine tool makes would tell anyone that the system was working and not stationary!

HF driven tubes are a bit of a pigs ear. They should be a touch more efficient, but they radiate all sorts of high frequency hash. This can cause the effect you are experiencing. I would never use HF gear in a workshop, mucks up my radio!


Adam Harris11/10/2018 21:54:17
470 forum posts
26 photos

Yes well I found some very convincing advocates online for twin HF tube in the workshop along the lines of more efficient and no stroboscopics (the twin cancels each other's frequency out), but they did not come from this illustrious forum (perhaps Practical Machinist?). Anyway no warnings mentioned of the Pig's Ear and RCD's!

Edited By Adam Harris on 11/10/2018 21:58:49

Edited By Adam Harris on 11/10/2018 22:01:29

John Haine11/10/2018 22:14:57
3272 forum posts
175 photos

Have replaced 3 fluorescents with LED "tubes" and use LED work lights almost exclusively in the workshop. No problem with strobe effects.

Adam Harris11/10/2018 22:48:59
470 forum posts
26 photos

John, did you replace with LED because of RCD tripping problems?

ega11/10/2018 22:49:51
1790 forum posts
153 photos

Plus 1 for the LED tubes - a revelation.

Alan Waddington 211/10/2018 23:39:36
505 forum posts
87 photos

Iv’e recently ditched the fluorescents and fitted eight of these bad flicker or strobe effect, instant switch on, and flipping bright


Edited By Alan Waddington 2 on 11/10/2018 23:40:56

Sandgrounder12/10/2018 07:08:29
199 forum posts
6 photos

I use LED floodlights and LED GLS bulbs in my small workshop and I do get a slight strobe effect, but like Andrew says in post 2 the noise of the machine is more than enough to warn you that it's working.

Gary Wooding12/10/2018 08:11:54
753 forum posts
194 photos

I replaced the 3 twin 6ft fluorescent tubes (not HF) in my workshop with LEDs. My old eyes cannot detect any flickering or strobe effects. The LEDs are far better with a cleaner, purer, light. And instant on/off.

David T12/10/2018 09:53:30
74 forum posts
14 photos

I have two single fluorescents in the workshop; never had a problem with nuisance RCD trips, and never noticed a stroboscopic issue either. Surely any stroboscopic effect would be limited to harmonics of 50Hz though? So any stroboscopic effect may lie dormant for years until one one day something just happens to spin at the required RPM?

KWIL12/10/2018 10:15:17
3294 forum posts
63 photos

As an experiment I have in the past, wound up the spindle speed as set by the VFD from 0 to max and have not found this alleged strobe effect.

Andrew Tinsley12/10/2018 10:46:59
1170 forum posts

I don't want to stir controversy. However the resounding vote for LED tubes may be a mite misleading. People usually swop from fluorescent to LED tubes because they are dissatisfied with the lighting levels. They are then amazed how bright the LED tubes are. However they are usually comparing old worn out fluorescent tubes with new LED tubes. Need I say more?

With regard to the colour temperature of tubes. There is a much wider choice of colour temperature in fluorescent tubes than for LED tubes. People never ask for a colour temperature when they buy tubes and therefore usually get around 3000K tubes, as they are the most common.

LED tubes are not necessarily free of flicker, it depends on the circuitry of the drivers. Having said all that, LED tubes are more efficient. At the current time they are also quite a bit more expensive, which tends to reduce their efficiency advantage over life. One other thing to note is that the claimed lifetime of LEDs is usually very optimistic. The life is critically dependent on temperature. The higher the running temperature, the shorter the life! It only takes a small temperature rise to significantly reduce the lifetime to failure.

Obviously LEDs are the future, but right now, the advantages are not as large as people think. When the chokes fail on my fluorescent tube installation, I will probably change to LED tubes, until then, I shall keep my 6000K fluorescent tubes. By that time, the LED tubes will be significantly cheaper than they are now.


SillyOldDuffer12/10/2018 11:40:59
6193 forum posts
1345 photos

Those who've failed to find stroboscopic effects haven't looked hard enough!

That said, the effect is often small and I doubt it's much problem in practice in a small workshop where the noise of a machine running is often enough warning in itself.

But imagine you're in a large machine room lit entirely by fluorescent lights all flickering together at 50Hz with several noisy machines racketing away in the background. Perhaps you're wearing ear-defenders. Also, you're unluckily turning a strongly contrasted lump of bright steel and it happens to be rotating with just the right diameter and rpm to sync with the lights. A moment's inattention and you could get caught. Bit unlikely, not impossible. Actually, stroboscopic effects are much more obvious with largish objects like poorly lit fan-blades and gear wheels. Beware of them!

I have a mix of HF and conventional fluorescent lighting with HF over my lathe. It creates an effect not unlike strobing because the light bounces off the rotating jaw into my eyes at the same angle:


Not a camera trick, the photo is very like what I see - a chuck that at a careless glance looks as if it's stopped. As with a lot of accidents, several factors are often required to come together. I might fall for it if I was tired, drunk, distracted and unlucky. But not normally!

The other end of my workshop has ordinary fluorescent lights. Here I notice true strobing once in a while, but it's not strong enough to fool me. It's hard to imagine it causing an accident. The best way to see strobing is to spin an object with black stripes on a white or shiny background in low ambient light.  Used to be quite hard to see adjusting the speed of a teleprinter governor with a neon bulb and very obvious at the strobe lit Discotheque of my youth.

Another factor may be the age of the tube and the type of phosphor inside. Some tubes flicker a lot more than others, and old tubes seem worse than new ones.

HF tubes flicker much faster than the human eye can detect and the effect isn't synchronised between lamps. Like LEDS, they don't strobe.


Edited By SillyOldDuffer on 12/10/2018 11:45:23

KWIL12/10/2018 12:52:25
3294 forum posts
63 photos

Interesting 2 jaw chuck does not fool me into thinking it is not rotating.wink

Brian Sweeting12/10/2018 14:15:33
437 forum posts
1 photos

Just for info but we used to check our contactless tachometers by pointing them at a fluorescent tube to check that they were reading correctly. 3000rpm IIRC.

Andrew Tinsley12/10/2018 14:47:01
1170 forum posts

In an amateurs workshop, strobing is unlikely to fool anyone into thinking that the machine isn't in action. Large workshops with multiple people are another thing altogether.

Yes I calibrate my tachometer with a fluorescent tube. You can still get the effect with a tungsten filament lamp (although much less of a variation). The eye can't respond to 50 or 100 Hz unless you are a very odd man out, so this isn't the flicker you see with an old fluorescent tube.

I reiterate that LEDs are not always flicker free. It depends on the electronic drivers. Some of the cheaper drive circuits produce the same sort of 50Hz flicker as a fluorescent. You get what you pay for in driver circuits.


HughE12/10/2018 15:20:11
122 forum posts


Back to your OP question and the tripping of the RCD. This could only happen if there was a imbalance of> 30mA between the L and N. I do not know what the driver circuits in these are like but I suspect there is a some form of filter circuit that could be the cause. Did you really mean you have connected them in series?


Neil Wyatt12/10/2018 15:48:14
18140 forum posts
713 photos
77 articles

My dad had several cardboard 'records' with circular patterns of lines in the workshop at his shop. They were for adjusting the speed of record players together with a suitable light.

I recall some decks had a built in pattern round the edge of the platter and a small neon.


Mike Poole12/10/2018 16:06:41
2700 forum posts
64 photos

My Pioneer deck still has the strobe track cast in the platen and is illuminated by a neon source, it is getting on a bit now as it was new in about 1978


Adam Harris12/10/2018 16:34:40
470 forum posts
26 photos

Hi Hugh, thank you for directly addressing the RCD issue. Yes I wired the two in series and RCD tripped after a few seconds. I have now wired these two independently with different switches (although both switches coming off the same supply cable) and everything is fine. What does this mean in terms of interference between units. Should one never wire fluorescents in series? Or is it the starting of both at the same switch that causes excessive surge? In other words is series wiring ok as long as there is a startup delay between each (ie an on/off switch between each)?

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