[RFI] CFL's & UV - Hoax or Real? Real but Overstated?

w3kl at w3kl.com w3kl at w3kl.com
Mon Feb 23 22:09:08 EST 2009

At the heart of all fluorescent bulbs (tubular, miniature, or CFL) is a low pressure mercury discharge.  When excited, a mercury discharge will emit copious amounts of UV energy at 254 nanometers (nm) wavelength.  This is in a wavelength range that is canonically called the "UVC" band.
It also happens that 254 nm UV is close to the wavelength at which DNA will break down.  Hence, low pressure mercury discharges are very useful for killing bacteria, which is why water and air treatment systems employ low pressure mercury lamps.
For reference, visible light is usually taken to be between 400 nm (deep blue) and 700 nm (deep red).
One achieves visible light from a low pressure mercury lamp by coating the quartz (fused silica) bulb envelope with a phosphor that is excited by the 254 nm mercury line and re-emits a broad band of light in the visible range.  Hence, the key to a "good" fluorescent lamp is the efficiency of the phosphor.  "Good" in this sense means the ability of the phosphor to create broad band white light.  Most phosphors are good at converting 254 nm into what our eyes perceive as blue light along with some orange and red which makes the light appear as "cool white".  This is good for task and office lighting, but most consumers reject cool white in favor of warm white light which contains more red.  However, it is amazingly difficult (in relative terms) to make a phosphor that can efficiently make red light.  Most of the existing body of knowledge on phosphors for creating visible light was pioneered by the Russians 50 years ago.
Now, because the phosphor in a fluorescent tube cannot convert ALL of the 254 nm UV and because there can be "gaps" in the coating of the quartz tube, it's definately possible for ANY fluorescent bulb, compact or not, to emit some UV.
Finally, it's not that it's very difficult to measure UV from a fluorescent tube...instead, one needs a device that can measure efficiently at 254 nm and block light above approximately 380 nm.  This requires a very good low pass filter.
Such devices, called radiometers, are available and can easily measure the leakage UV from a fluorescent tube.
Hope this helps.
73, Jeff

Jeffrey K. Okamitsu, PhD, MBA

--- On Mon, 2/23/09, kd4e <doc at kd4e.com> wrote:

From: kd4e <doc at kd4e.com>
Subject: [RFI] CFL's & UV - Hoax or Real? Real but Overstated?
To: "RFI List" <rfi at contesting.com>, "tvi-rfi-emi at mailman.qth.net" <tvi-rfi-emi at mailman.qth.net>
Date: Monday, February 23, 2009, 8:52 PM

Just received this from a family member and wondered if 
anyone has
looked into it?



Thanks! & 73, doc, KD4E
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