----- Original Message -----
From: Terrence Fugate
To: on4ww
Sent: Wednesday, December 29, 2010 5:55 PM
Subject: RFI

I enjoyed your EMI web page. You mention halogen lamps as a possible RF noise source.
Dr. Charles Counselman (W1HIS) mentioned to me that he had a small, quartz-envelope, halogen gas-filled, incandescent light-bulb with a broken tungsten filament that generated terrible RF noise.
The filament was open when cold, when its conductance was measured with a test voltage of 2 V or less. The microscopic gap at the break in the filament arced over and the arc would conduct extremely well, with very little voltage drop, if normal operating voltage of 12 V was applied to the filament. With normal operating voltage, the bulb lit apparently normally.

I worked in the TV industry from 1972 through 2008 until a slip and fall on the job injury made work impossible. Over that time I experienced several studio halogen lights that exploded. In several cases I had been 'sunburned' under a light that exploded later. I now suspect that the open filament and arc are much more common than realized, and the arc eventually causes the lamp envelope to shatter. It is an interesting experience to have hot quartz fall on you!!! I am blond, blue eyed and have fair skin, so I am somewhat susceptible to UV. I asked another engineer to watch for studio lamps that 'sunburned' her. She too is blond, blue eyed and fair skinned. Over the last year she pulled three lamps from service and I tested them at home and sure enough, they all started producing severe RFI after they warmed up. One exploded.

Most TV facilities are changing over to HID lights, high intensity fluorescent lamps, or most recently high power LED lights. The LED lights are favored because they are the most efficient and can be programed to change color temperature to track the non linear color temperature versus light level of modern TV cameras. The cost saving is significant. We used to run about 25kW for lighting, and a similar amount for cooling. Their electric bill has dropped considerably and they were able to replace the ancient air conditioner with a much smaller and more efficient unit.

I doubt if normal incandescent lamps argon or nitrogen gas will support an arc. I have never seen one and by shaking a failed halogen to cause the filament to completely fall off the supports produced a 'light' that would arc at 300V AC.

I just thought you might want to add another possible RFI source from halogen lamps. Since quartz is transparent to UV, arcs will easily cause those of us with sensitive skin to 'burn'.

Terrence Fugate
I hold an extra class amateur license, but I am really a shortwave listener at heart. Although my friends now say I spend more time IDing various RFI sources.