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Information on UVC light
UVC is often used for sterilization. It can be found all over the place. You see them at the barber or hair stylist (usually tools are left 45 minutes or so in a cabinet), many medical facilities, dentists, and even entire rivers (the water flows over the high power lamps in seconds). Yes, it is quite common for people to use UVC lamps in their aquariums to control bacteria, fungi, and algae. These lamps are different than the ones used in bird or reptile cages.
UVC light is an even shorter wavelength of light than we normally think about. UVA (320 to 400 nm), UVB (280 to 320 nm), and UVC (200 to 280 nm) of which we all know UVA and UVB is bad for our skin and eyes. UVC doesn’t occur as naturally as UVA and UVB. With its short wavelength its intensity does not “reach far” so it is readily absorbed by the atmosphere. The UVC spectrum, especially the range of 250–270 nm, is strongly absorbed by the nucleic acids of a microorganism and with that is the most lethal range of wavelengths for microorganisms.
You can think of UVC light as reducing its delivered irradiation to be the inverse square. So twice the distance, a quarter the power delivered. For example, welding generates a lot of UV light. Someone who welds is often exposed to significant amounts of UVB and UVC light, on top of the standard UVA light and this is because the arc from welding is a full spectrum light source and often the operator is inches from it. If you research the problems welding professionals have as the age, you will find that their exposure to full spectrum light causes them to have cancer and other issues in tissue not normally seen. Event he person that is often right with them (the grinder) isn’t as high risk.
Inactivating the DNA of living things with UVC takes delivered energy (dose). You can deliver significant amount over a short period of time or a little bit over a long period of time.
Most surfaces do not reflect much UVC light. Polished aluminum is one of the only surfaces that is affordable to reflect UVC light. It is still only roughly 30% efficient at reflecting UVC light. However, if the aluminum is sprayed then it can reflect up to 80% of the UVC light. UVC light also destroys most surfaces with exposure, including aluminum.
UVC light is usually created with a low pressure mercury bulb with a quartz glass tube doped with cesium. It is essentially a fluorescent light without any phosphor inside. This design generates a 254nm wavelength. The cesium absorbs the 185nm wavelength (185nm creates a lot of ozone). The next most popular is a high pressure lamp that is closer to design of a HID lamp on modern cars. These have a much wider spectrum and aren’t as readily available at an affordable price.
Ozone, by the way, is created by UVC light. Especially the shorter wavelengths. It is one of the reasons why we have an ozone layer… Ozone, at room temperature mostly degrades over about 8 hours. Ozone is also excellent as an oxidizer which is also germicidal.
Lastly, UVC light is now being generated by LED. The nice thing about LED is that it is small, directional, and has specific wavelengths. Part of the problem is that it is directional which can make it difficult to get enough radiation in a large area. However, it allows you to target specific issues.
Remember, UVC light is bad for DNA, including yours. Do not look at the light when it is on.
Ideal setup
An ideal setup would be several different short wavelength (say, 235nm, 255nm, and 275nm or so), very short distance (under an inch between the light source and the target), full immersion (many light sources), and for a period of time that is sufficient. The more power, the less time to receive a sufficient dose. The dose required depends on the wavelength, the power, the distance, the surface, and the quantity of material to destroy.
We aren’t likely to have a lab. We also don’t want to spend a lot.
What we’re going to build
We’re going to use aquarium low pressure 253.7nm bulbs. They are cheap (usually under $30/each), easily sourced, and we know they are effective at killing algae.
We need a box we can put the light sources in so that the light doesn’t leak out and injure (irradiate) humans, pets, or materials. Ideally, it would be a box that doesn’t have any straight-through gaps for light to leak out of. The better it seals the better it will work anyway, because since ozone is created if the ozone is contained in the box then it will also act as a germicidal.
We need a way to maximize the amount of ultraviolet radiation absorbed or at least not waste it and get the light on as many areas as possible without disturbing the items. Polished aluminum works best but it is difficult to get and maintain. We’ll use aluminum foil.
What we’re going to need
- 6x UV-C light sources, these are purchased from Amazon but I recommend getting wherever you can find cheapest.
- A box to put the light sources in, these are what I used from Amazon but I sourced them locally for $14.
- A reflector (aluminum foil), I used 18″ food service aluminum foil because the height of the container is the same as the width of the foil which can be purchased way cheaper than this on Amazon.
- Tape to fasten the reflector (aluminum tape), it can be sourced in the ductwork section of most home improvement stores for $8 or this one on Amazon.
- A convenient way to turn all the lights on and off, I used a 6-outlet power strip from Amazon.
- Something to lift items off the floor of the bin so the bottom light can get the bottom of the objects. I used a wire closet shelf to fit, but you can use anything like a cooling rack for an oven. Remember most objects absorb UVC.
Assembly
