# Germicidal Lights?



## CroMAGnet (Nov 10, 2004)

Just up late here tonight and was wondering. Seems like lots of smart people here at CPF that might wonder through this with me. 

I had an inspiration to figure out some type of appliance that can hold our toothbrushes in between brushing to sterilize the bristles. It can be a small clip light with a UV protective sheild or a stand that hold multiple brushes. Hmmm... (google search revealed one already in China)
Ultraviolet Radiation Tooth Brush Disinfector with Automatic Control System 

I requested a sample. We'll see if I ever get one.

(More google info)
Germicidal lamps are Low-Pressure Mercury-Arc lamps that emit radiation peaking at 253.7nm(UV-C). This output at 253.7nm is highly effective to inactivate microorganisms such as bacteria, virus, yeast and mold.

Warning: Protect your eyes and skin when operating Germicidal Lamps.
Equipment should be designed to completely screen or filter UV-C radiation.

*One problem might be the cleaning between the bristles: (The Chinese unit looks like it rinses or something)* 

The University of Ottawa states; Ultraviolet (UV) lamps in Biological Safety Cabinets (BSCs) are intended to destroy microorganisms in the air or on exposed surfaces. However relying on UV lamps may give personnel working in BSCs a false sense of security. UV lights have limited penetrating power and are only effective when the lamps are properly cleaned, maintained, and checked to ensure that the appropriate intensity is being emitted. The UV lamps attract dust and debris and thus reduce the transmission of the germicidal effect. In addition, many people allow the lamps to surpass their effective life span. When the terminal ends are blackened even slightly, they have lost their effectiveness even though they still glow blue-violet. If UV lamps are used it must be remembered that UV light can be harmful to the eyes and skin and should therefore be turned off when occupying the room.

MORE INFO: In order for ultraviolet light to kill bacteria, the rays must directly strike the microorganism. Germs floating in the air or on an outer surface may easily be reached by the ultraviolet rays and, therefore, are readily destroyed. If the bacteria or mold spores are hidden below the surfaces of a material or are not in the direct path of the rays, they will not be destroyed.

The exposure to ultraviolet necessary to kill bacteria is the product of time and intensity. High intensities for a short period of time, or low intensities for a long period are fundamentally equal in lethal action on bacteria disregarding the life cycle of the bacteria.

Ultraviolet light will not penetrate most substances. Meat, cloth and food will not be sterilized by irradiating with ultraviolet because the rays do not go beneath the surface. Even ordinary glass is opaque to short wave ultraviolet. Among the very few exceptions to this rule are clear water, which does permit some penetration, certain plastic films and specialty glass.

It has been an accepted practice to consider 0.5 microwatts per square centimeter for an eight-hour exposure and 0.1 microwatt per square centimeter for a twenty-four hour exposure as the allowable maximum intensity of 254nm ultraviolet radiation incident upon people. These germicidal lights generate considerably more than this, so you must take precautions to shield yourself and others when operating the UV light.

Sounds outlandish. I'd be surprised if it sparked interest for discussion but what if the bristles were simply clear? /ubbthreads/images/graemlins/sleepy.gif


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## CroMAGnet (Nov 10, 2004)

/ubbthreads/images/graemlins/bumpit.gif for weirdness


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## sithjedi333 (Nov 10, 2004)

Interesting concept. In the medical center labs we had UV lights to sterilize the hoods in which we did tissue culture experiments. These were left on 24/7, and only turned off when we were conducting experiments. Before and after each experiment, we wiped the hood down with alcohol to remove and kill anything remaining.


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## EricB (Nov 11, 2004)

In the 1940's NYC had a test subway train with germicidal lamps called a "precipitron". That was eventually removed as not a good idea. I always womdered what this looked like. At a 253, that would be invisible, but since that is just the peak, I wonder if there was any visible light put out by it.


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## jtr1962 (Nov 11, 2004)

The subway train with germicidal lamps was a failure because the lamps only were strong enough to remove bacteria in the lamp housing. If you could get something strong enough to sanitize the entire train it doubtless would have affected people's eyes.

The 253.7 nm lamps give off a dim bluish-purplish glow. A 253.7 nm tube is basically a fluorescent light without any phosphors. The primary emission is at 253.7 nm but there is enough in the visible range to give a noticeable glow, at least on the ones used in EPROM erasers which I've seen.


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## The_LED_Museum (Nov 11, 2004)

The first two items at the top of http://ledmuseum.home.att.net/glow4.htm are shortwave ("germicidal") fluorescent lights.


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## CroMAGnet (Nov 11, 2004)

Hey... What about making a light that is handheld, maybe plugs into a wall and has a strong bulb with the correct specs to kill germs and bacteria. The you just stick your toothbrush in the protected bulb area and rub something that separates the bristles apart so the light can penetrate thoroughly??... /ubbthreads/images/graemlins/icon3.gif


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