Thread: fluro lighting

you know the main danger is that rotating parts of the machine will appear to be standing still.
i have never had any problem with this on a lathe.
my drill press is another story. if the belts are off and the motor running you would swear the motor pulley was standing still.
to counter the effect if present you just need a lamp with a incandescent globe pointed at the work area.

that fluro is used in areas where the atmosphere may have flameable gases/fumes

lot lot cheaper to just stick a normal fluro in...also you'll get more light than one which is covered or has a diffuser

not too keen on losing the diffuser, the lights going to be mounted about 2 feet above the lathe on the underside of a shelf, don't fancy getting coolant sprayed into it.

Having owned a lathe for a grand total of 2 days, I feel I'm well qualified to comment (not).

I was running my lathe today under flouro light and the chuck appeared to be rotating backwards. I guess at the correct speed it could appear to stop.

The stroboscopic phenomenon is well established and actually forms part of the course for Electricians / electrical engineers in England at least.

As has been said, it comes from the fact that fluorescent luminaires will strobe on and off at the same rate as the Hz of the supply.

50Hz in Aus will translate to a 50rps / 3000rpm speed in a rotating machine. If the fluorescent tube is the sole source of light, at 3000rpm (give or take a few rpm), rotation will appear stationary.

The big danger does indeed come from big machine shops where the background noise is so high, ear protection is being worn and there is no way to tell if your machine is running by noise alone.

Ironically, the nature of big machine shops invariably being supplied by 3-phase electricity means a properly installed lighting setup negates the stroboscopic effect.

Correct practice in this instance is to wire each successive fluorescent fitting to a different phase in order. This means that each set of 3 fittings fires individually on a different phase, negating the stroboscopic effect.

A much simpler way of dealing with it in a smaller workshop / home environment, if it's a problem, is to add a standard halogen / incandescent type light to the area around the machine. Maybe an anglepoise type thing focused on the work area. Cuts out the stroboscopic effect altogether.

that was a greaT explaynation. if the power was 60 hz at waht speed would this happen? is it 2800rpm?

Originally Posted by JNorton

The stroboscopic phenomenon is well established and actually forms part of the course for Electricians / electrical engineers in England at least.

As has been said, it comes from the fact that fluorescent luminaires will strobe on and off at the same rate as the Hz of the supply.

50Hz in Aus will translate to a 50rps / 3000rpm speed in a rotating machine. If the fluorescent tube is the sole source of light, at 3000rpm (give or take a few rpm), rotation will appear stationary.

The big danger does indeed come from big machine shops where the background noise is so high, ear protection is being worn and there is no way to tell if your machine is running by noise alone.

Ironically, the nature of big machine shops invariably being supplied by 3-phase electricity means a properly installed lighting setup negates the stroboscopic effect.

Correct practice in this instance is to wire each successive fluorescent fitting to a different phase in order. This means that each set of 3 fittings fires individually on a different phase, negating the stroboscopic effect.

A much simpler way of dealing with it in a smaller workshop / home environment, if it's a problem, is to add a standard halogen / incandescent type light to the area around the machine. Maybe an anglepoise type thing focused on the work area. Cuts out the stroboscopic effect altogether.

For 60 Hz mains the work would appear stopped at 3600RPM if driven by a dog and drive plate. (60 cycles /sec x 60 seconds /minute =3600 cycles /minute). However a lathe chuck might have multiple jaws (2, 3,4 and 6 being most common), and the number of jaws increases the chances of a jaw being near the position that a different jaw was in in the last light burst. This is what causes the causes the apparent slowing, stopping or reverse rotation associated with strobing.

The issue is a compound one, as the fluoro fires two bursts of light for each cycle of the mains, one on the positive half cycle and one on the negative, so 100 bursts per second for 50 Hz mains.

The human eye merges these bursts as the transition is too fast for the eye to follow. This is based on the same principal as TV/ computer screens etc where the screen is refreshed at a rate faster than the eye can percieve, so that the response of the eye is the limiting factor that merges a number of discrete images into a smooth motion.

The issue is compounded with fluoro's in proximity to rotating machinery because moderate differences between the rotating device and multiples of the lighting frequency generates virtual images at the sum and difference frequencies of the light bursts and work speed. Some of the difference frequencies produced are low frequencies that the eye can register as individual images, giving the impression that the machine is stationary or operating at an absurdly low speed which people can perceive as slowing to stop and sometimes try to brake with their hand, (OUCH).

The other potential issue with the sum and difference effect is that over extended periods e.g. a typical working day, the apparent low frequency flicker effect can place a very significant strain on the eyes, which is one of the reasons for the general industrial concerns about operating fluoros above rotating machinery.

Other types of discharge lighting will generate similar effects, but incandescant lights like the the traditional tungten filament and halogen lights don't because the light is emitted by a heated filament with little variation in brightness, not as a cyclic discharge.

Using three phase power to fire three seperate tubes in a fitting would help to smooth the light emission from the fitting, but there would still be peaks and dips with the potential to generate hazardous sum and difference frequencies with rotating machine tools.

Sum and difference frequencies are generally not an issue with saws, planer heads, etc due to the high speeds and number of teeth or cutters involved. Eg a three blade planer head running 4000RPM is presenting a cutter 12,000 times a minute, or 200 times a second, so any strobing differences with a 100Hz light source would be in the order of 100 Hz and well above the frequency threshold of the eye.

I might be wrong here, but it was my impression that the machine could appear stationary at any speed which was a multiple of the frequency. So if the chuck is rotating at 3000 RPM, it could appear stationary with both 50 and 60 Hz. speeds of 500, 1000, 1500 RPM would be in the danger zone with a 50 Hz supply too. As has already been mentioned, items like chucks or saw-blades with multiple identical looking parts (jaws and teeth in the examples listed) would have many more chances of this phenomenon occurring. There may be fluorescent tubes with long persistence phosphors which minimise the effect, and I think that the compact fluorescent globes, with electronic ballasts, run at very much higher than line frequency which would assist in minimising the problem because the phosphors might persist long enough to stop the strobing effect.
Rob

Originally Posted by kraits

told me not to use fluro lighting above a lathe, apparently it causes a strobeing effect

It's quite well known, people even use the effect as a cheap tacho - Lathe Tachometer. Won't work in Oz, 50Hz vs 60Hz and all that. Google will turn up one that works here.

(Nice to see the Biggles bloke has found a new hobby.)