Low EMF/Interference Lighting

EMPOWERTORCH · #1 02-05-2003, 02:16 AM

The Company I am employed by is about to revise its calibration laboratory. One of the requirements for the Laboratory is that electrical equipment used within the Electrical Metrology section of this proposed new Lab must not generate RFI, mains hum or electromagnetic/static fields liable to cause interference to the precision measuring equipment used therein.
The present Laboratory uses fluorescent lighting; but this is a well known source of interference.
Filament bulb lighting has been proposed but this is going to upset the precise temperature control of the lab, and it has lousy colour temperature.
The Lab needs general lighting as defined in the standards laid down by UKAS for laboratories (in terms of brightness).
What type of lighting would you suggest?
URL's of UK suppliers would also be useful.
Matt.

Lighthouse · #2 02-08-2003, 06:55 AM

By using electronic ballast in the fluorescent fixtures, the primary source of electromagnetic interference can be greatly reduced. However, depending upon the sensivity of the lab equipment, it would be worthwhile to verify through testing and measurements that the higher frequency/voltage that an electronic ballast utilizes will not become a replacement interference issue.

One of my early experieces with electonic ballast and noise/interference reduction came from one of my customers around 1984 or so...it was a lawyers office, and this lawyer had just launched a video teleconferencing center to allow remote video depostions to be taken using worldwide fiber optic links.

The job specifications required high Kelvin light output and electonic ballast. This was at a time when these ballast cost over 123U$D each. Had to provide one fixture with two ballast and the high K lamps in order to gain product acceptance in terms of noise and electronic radiation before they would commmit for the remaining ten or so fixtures.

Final result is that they were able to do their work without interference from the fl. fixtures.

Interestingly enough, I ended up replacing their incandescent ceiling mounted recessed light fixtures...they were using dimmer switches which when used in low to mid range levels provided a high frequency noise from the lamps elements as they resonated on the varying frequeny provided by the dimmers. It was like an eerie high pitched UFO type sound.

We jokingly called them the vienese/sp? light choir due to the high pitch singing.

The EMF field intensity will vary as a function of distance. It may be possible that by going to electonic ballast and moving the light fixtures further away from the testing equipment that an additional field strength reduction may help out.

If memory serves correctly, the reduction is something on the order of an increase in field intensity by the square, for each 50% distance reduction. Haven't had second cup of coffee yet, so this will need to be verified. [img]images/icons/grin.gif[/img]

You are absolutely right in that incandescents will provide much more heat than the fl. fixtures.

I believe that you may be able to use the electonic ballast in your lab. Other considerations to review for EMF reduction include:

Keeping the lighting and lab equipment power circuits entirely separate. Do not allow these circuits to share neutral conductors.

Install additional grounding conductors in all circuits that are unbroken from the point of use back to the breaker panel. In very sensitive circuits, this ground will need to go all the way back to the ground rod.

Do not allow the circuits for the lab equipment to come within several feet of the lighting fixtures.

Hope this helps a bit.
Lighthouse

EMPOWERTORCH · #3 02-10-2003, 06:45 AM

Lighhouse,
Thanks for the info. I've passed it on to the Head of Laboratory and he is pleased to have the info.
CPF really does become useful at work!

Willmore · #4 03-06-2003, 01:29 PM

Sorry to be so late, but there's always the possiblity to use incandescent lighting with DC power, right? Absolutely no interference from that.

Wylie · #5 03-07-2003, 11:24 AM

EMPOWERTORCH,
Just use remote ballasts outside the work area and make sure everything is grounded correctly.

Willmore · #6 03-07-2003, 03:15 PM

You'll still get the magnetic field from the loop formed by the fixture and the bulb not to mention th electrostatic field from the lamp.

Zelandeth · #7 03-11-2003, 04:28 PM

Semi Off topic, but you're not the only one to have encountered the "vocal" incan lamps. I've an old incan floodlight (200W) from a small pub stage, I use it as an uplighter in the corner of my room usually, quite often it "rings" like someone running a finger round the edge of a crystal glass. Thought it was just the one bulb, but it was replaced a couple of weeks ago, and still does exactly the same thing. Took me darn near a month to actually track down where the WIERD sound was coming from...