Cleaning With Light
If you’ve spent any time under the sun on a long, hot, clear day, you’ve probably gotten a wicked sun burn. I may have overcooked myself a bit during our nice Easter weekend too. This brings up an interesting thought: what happens to airborne pathogens exposed to the same light? A sunburn is the result of millions of skin cells being irradiated by UV Radiation. Sunlight contains UV, Ultra-Violet, which can cause skin cancer in high enough exposures. It’s not dangerous in the same way X-Rays are, those would be lethal with a few hours of exposure. UV is weaker, but it still wreaks havoc on small cells.
Messing With Molecules
Let’s start out with some basic physics. We’re going to ignore the whole “particles & waves” thing for now and just say that all light is made of particles called Photons. When you turn on a light, it spews out photons, that bounce off the wall, lose some energy, strike your eye, and then you perceive the ‘color’ of that photon. What happens is the photon rams a cell in your eye with a certain amount of force, it’s energy, and that tells you it’s ‘color’.
To the 3 physicists reading this, shut up. I know it’s more complicated.
The problem happens when we give that photon more speed, more energy. Eventually, the photon moves too fast for our eyes to detect. It’s not visible light any more. It becomes what we consider Radiation. Above visible light, there is Ultra Violet Light, UV Radiation. Above UV is X-Rays, then Gamma Radiation. This is a lot of energy for a little particle to have. It stops so much bouncing off things as it does just blasting through them.
The transition from ‘harmless’ to ‘we really shouldn’t be here’ happens with UV Radiation. Lower powered UV-A radiation is mostly harmless. To get cancer or anything serious from UV-A, you’d need to spend weeks, months, out under the sun all day. It’s a health issue for outdoor workers like farmers, police officers, and life guards on the beach. UV-B radiation is more powerful, it usually gets stopped by the Earth’s upper atmosphere. This radiation can start to mess with your cells and DNA. It’ll cause sunburns and cancers. UV-C is a step above UV-B. It’ll basically destroy anything it touches. It’s only mildly safer than X-Rays. Luckily, the atmosphere stops it, and we have to artificially create it, mostly.
When a UV Photon, B or C strikes an atom, it stands a pretty good chance of knocking an electron off the atom. We call this Ionizing Radiation. This wouldn’t be too big of an issue except the molecules in our cells and DNA are often bonded by their electrons. Two molecules come together and depending on their electron-charges, they’ll share an electron, and that binds them together.
Our bodies are defined by our DNA. You can imagine what happens when we start blasting at our cells and genetics with a shotgun. Things start to fall apart. Genes are removed. Mutations occur and anything from cancer to downright freakiness can happen. At best, our cells will have to repair their organelles and walls. At worst, those cells become a cancer and cause trouble.
The thing is though, we’re composed of about 37.2 Trillion cells. If even a few tens of thousands of skin cells become damaged by UV Radiation, we can grow new cells. Things like pollen, bacteria, and whatnot have only once cell. There might be millions of that same species, but the individual organism can’t come back. And there isn’t a bigger organism to help shield any one cell. For a person, your skin protects the rest of you. For bacteria? Nothing.
The same can be said of Viruses, Mold, and basically any other microbial thing. There are some tiny organisms like mites and tardigrades that are multicellular, but they’re not really going to cause us issues.
Regular sunlight will cause some damage to these things, but they’ve evolved to deal with that, mostly. Viruses are most likely to be killed in sunlight. Some viruses have evolved resistance, but many can’t survive outside a body. We need to amp up the power a bit, go past the UV-A and UV-B we typically expose ourselves to and uses UV-C.
So, the solution? Install UV Lamps in strategic locations inside the various ducts, air handlers, and so on of your HVAC System. These lamps need to output mainly UV-C radiation. We also need to put these lamps where they won’t shine on people. We can survive UV exposure, but UV-C is the borderline killing people one. Let’s limit that exposure.
Numerous manufacturers provide kits for UV sterilizers. These kits exist for water and air sterilizing. Running one of these lights 24/7 will generally cost $20-$50/year, depending on the lamp and local utility rates. Bulbs range in lifetime from 1-2 years, though we are starting to use UV-LEDs which could have longer lifetimes.
The key benefit of these lights is that they can break down allergens, bacteria, and viruses without the need for a filter. A filter only captures these problems. A UV Light obliterates them. These won’t stop other things though, chemicals and other airborne pollutants may come through entirely unharmed. It’s a bit of a game of chance. It depends on their exact molecular composition. You should still use a filter, but perhaps with a UV Light, you can get away with a slightly weaker filtration setup.
UV Light also causes a bit of collateral damage. Everything is made up of atoms and molecules. UV Light will cause damage to anything it touches. Even metals will decay when exposed to UV Radiation. They’re made of molecules that are bonded together, the same as your DNA. UV bombardment will eventually break down those bonds too. The issue is just more accelerated when using UV-C radiation.
Consider for example, leaving a chair outside. If you left it in the yard, under the sun 24/7/365, it would eventually deteriorate to nothing. Thicker things like wooden benches and chairs would be be mostly unharmed. Synthetics, plastics, and thin materials however, would deteriorate more rapidly. This is especially true of unpainted metal. One of the key parts of your car’s paint is a UV protection layer, molecules which won’t react to UV light.
In practice, this means the HVAC Equipment housing your light may be more sacrificial in the longterm. In our research, we came across reports of ducts, drain pains, and coils being damaged by UV Light. Typically this took 2-5 years to actually manifest as a problem. We have always recommended twice-annual equipment inspections for both heating and cooling equipment, so we believe any UV-Damage can be detected and repaired before it becomes an issue.
You should of course, also consult your HVAC Contractor on what is best for your particular circumstances.