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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Jonathan Johnson on March 26, 2014, 08:12:45 pm

Title: Fluorescent light ballasts
Post by: Jonathan Johnson on March 26, 2014, 08:12:45 pm
Not sure if this is the right forum for this.

Does anyone have any insight into how different types of fluorescent light ballasts affect sound systems?

How about other conditions such as failing lamps or improper grounding of fixtures? How would that affect sound systems?

I know that conventional wisdom is to not run signal wires near fluorescent lights. However, I'm wondering if that only applies to certain types of ballasts. The wisdom is old, but electronic ballasts are new. Magnetic ballasts operate at 60Hz; some of the electronic ballasts step up the frequency to reduce visible flicker.

Could it be that with a newer ballast it's no longer a concern? If it is necessary to run wires near fluorescent lights, what mitigation steps can be taken to minimize noise in the signal?
Title: Re: Fluorescent light ballasts
Post by: Tim McCulloch on March 26, 2014, 08:28:43 pm
Not sure if this is the right forum for this.

Does anyone have any insight into how different types of fluorescent light ballasts affect sound systems?
  • Old-style T12 magnetic ballasts
  • Newer T12 or T8 electronic ballasts
  • High-output ballasts (T8/T5)
  • Commercial vs. residential ballasts
  • Standard vs. cold-start
  • "shop lights" with super-cheapo electronic ballasts
  • CFL recessed light (the kind where the bulb and ballast are separate)
  • Something else I haven't listed

How about other conditions such as failing lamps or improper grounding of fixtures? How would that affect sound systems?

I know that conventional wisdom is to not run signal wires near fluorescent lights. However, I'm wondering if that only applies to certain types of ballasts. The wisdom is old, but electronic ballasts are new. Magnetic ballasts operate at 60Hz; some of the electronic ballasts step up the frequency to reduce visible flicker.

Could it be that with a newer ballast it's no longer a concern? If it is necessary to run wires near fluorescent lights, what mitigation steps can be taken to minimize noise in the signal?

Some of the new switching supply ballasts spew RF well up into the UHF band.  GE is replacing all the fixtures in an office building because the lighting is interfering with Verizon users ability to watch TV on a cellphone while at work...  I have a post in the basement with the subject that says "The FCC says your lights are too loud".  There's a link in my post about the RF.
Title: Re: Fluorescent light ballasts
Post by: Steve M Smith on March 27, 2014, 03:52:41 am
GE is replacing all the fixtures in an office building because the lighting is interfering with Verizon users ability to watch TV on a cellphone while at work...

Whilst at work?  More reason to keep them in place!


Steve.
Title: Re: Fluorescent light ballasts
Post by: Mike Sokol on March 27, 2014, 08:13:17 am
Some of the new switching supply ballasts spew RF well up into the UHF band.  GE is replacing all the fixtures in an office building because the lighting is interfering with Verizon users ability to watch TV on a cellphone while at work...  I have a post in the basement with the subject that says "The FCC says your lights are too loud".  There's a link in my post about the RF.

About ten years ago I taught a seminar at a newly built church that had all kinds of in-ceiling lights with some sort of HF ballast. My RF headset mic would work as long as the beltpak was on the side of my body facing the receiving antenna. But if I turned the wrong way my RF signal dropped enough that the RFI from the lights would overcome the transmitter carrier and the receiver would output white noise at full volume level. Of course, shutting off the beltpak transmitter had the same result. The church staff told me they were having the same problem with all their RF mics on stage and couldn't figure out why. When I had them turn off every ceiling light in the building, all the RF mics worked properly. I told them that replacing all the ceiling lights was probably the only way they were going to get RF mics to work in the building. Nowadays you might swap out all the mics to digital technology, but who knows if that would have worked.
Title: Re: Fluorescent light ballasts
Post by: TJ (Tom) Cornish on March 27, 2014, 09:01:09 am
About ten years ago I taught a seminar at a newly built church that had all kinds of in-ceiling lights with some sort of HF ballast. My RF headset mic would work as long as the beltpak was on the side of my body facing the receiving antenna. But if I turned the wrong way my RF signal dropped enough that the RFI from the lights would overcome the transmitter carrier and the receiver would output white noise at full volume level. Of course, shutting off the beltpak transmitter had the same result. The church staff told me they were having the same problem with all their RF mics on stage and couldn't figure out why. When I had them turn off every ceiling light in the building, all the RF mics worked properly. I told them that replacing all the ceiling lights was probably the only way they were going to get RF mics to work in the building. Nowadays you might swap out all the mics to digital technology, but who knows if that would have worked.
If your mic was a Sennheiser, the problem was probably the squelch setting - turning that up a notch should fix the full-tilt white noise issue.
Title: Re: Fluorescent light ballasts
Post by: BobWitte on March 27, 2014, 09:15:18 am
This forum is a ballast!
Title: Re: Fluorescent light ballasts
Post by: Jonathan Johnson on March 27, 2014, 09:34:13 am
Some of the new switching supply ballasts spew RF well up into the UHF band.  GE is replacing all the fixtures in an office building because the lighting is interfering with Verizon users ability to watch TV on a cellphone while at work...  I have a post in the basement with the subject that says "The FCC says your lights are too loud".  There's a link in my post about the RF.

So instead of new technology being better, it's worse. Score: Public energy policy = +1; Wireless usability = -1.
Title: Re: Fluorescent light ballasts
Post by: Mac Kerr on March 27, 2014, 09:49:59 am
So instead of new technology being better, it's worse. Score: Public energy policy = +1; Wireless usability = -1.

Not new. In 2008 when we were doing "Passing Strange" on Broadway there was a scenic element that involved a wall full of fluorescent tubes. When it was lit it wiped out all the IEMs. The head electrician was very gracious in changing out ballasts for quieter ones. Different ballasts and helical transmit antennas from 20'-50' made it so everyone but the drummer could go wireless. The drummer had to have wired ears since his back was next to the wall. It just meant we could not check his ears before he went onstage.

Mac
Title: Re: Fluorescent light ballasts
Post by: Jonathan Johnson on March 27, 2014, 12:59:40 pm
The head electrician was very gracious in changing out ballasts for quieter ones. Different ballasts and helical transmit antennas from 20'-50' made it so everyone but the drummer could go wireless.

That's good to hear.

What would be great would be to have a list of brands and model lines that have proven to be RF-friendly (and maybe a list of problematic ones). With the end of incandescent lights as we know it, we'll probably soon see a lot of facilities switching over to fluorescent or LED, and it would be nice to know what products work well and what to avoid. Then when problems appear, we'll all be better able to recommend solutions.
Title: Re: Fluorescent light ballasts
Post by: John Roberts {JR} on March 27, 2014, 02:17:10 pm
I suspect RF ballasts that make significant RF are illegal. This may be a matter of nobody noticed until there was a wall of them, but I don't expect switcher ballasts to go away, until LEDs completely take over. They will need to be compliant with regulations.

JR
Title: Re: Fluorescent light ballasts
Post by: Jerome Malsack on March 31, 2014, 12:05:41 pm
According to the shure studies on Wireless, the RF noise floor will reduce the working distance of all wireless. 

Title: Re: Fluorescent light ballasts
Post by: Jerome Malsack on March 31, 2014, 12:09:24 pm
It would be fun to see what the RF noise floor would be at a DATA center like Google.  All the computers and the lighting issues.