A Primer on UVC Light – Part 1, by Dr. David J.

Whatever your take on COVID 19, it has certainly sharpened our focus on contagious disease. As we spiral downwards as a society, it’s a good bet that other contagious disease will be visiting us more often. It is important to remember COVID 19 has not made other diseases fade away, even if the media attention on this virus makes it seem that way. Preppers often focus on bullets, beans and bandages – weapons, stored foods and trauma-related first aid supplies, but realistically disease is probably the main killer in any long-term scenario.

The purpose of this article then, is to get you briefed and up to speed on a type of disinfection called UVC light, that can help prevent contagious disease. “UVC” is an abbreviation for ultraviolet light in the C spectrum and it’s a powerful tool. UVC has a long history of use in disinfection, because it works well and is cost effective. I want you to be able to use it both safely and effectively. In this article I mention a number of UVC products and manufacturers. I have no financial interest in any of them, and they are only included as examples.

Here are some of the things that make UVC unique and useful-

1) It uses much less energy than many of methods of disinfection. Most methods of disinfection require energy to make heat, boil water or steam. UVC just requires enough energy to power a light bulb.

2) There are no chemicals to dry out, spill, or lose potency over time.

3) It can disinfect things that are challenging to disinfect by other means. Like air, paper, fragile or awkwardly shaped items. Air disinfection is of special interest to many as this seems to be the main method of COVID 19 transmission.

4) UVC is an excellent addition in a resource-scarce environment where water and other types of disinfectants are in short supply.

5) It is important to understand that UVC light disinfects, but technically does not sterilize. Complete sterilization, kills all microorganisms and requires high levels of steam, heat or toxic gas. UVC inactivates up to 99.9% of pathogens, but does not technically sterilize. UVC light works by messing with the genetic material of microorganisms, so they cannot reproduce. Once microorganism cannot reproduce, they cannot spread and are rendered harmless.

6) Smell. UVC treated air often has a distinctive smell. Some of the odor is caused by the UVC light interacting with dust in the air. This smell can be distinctive, but is harmless and generally dissipates quickly. The other cause of odor is ozone. When UVC encounters oxygen, it can create ozone. Cheaper, broad-spectrum bulbs create more ozone than do higher quality, narrow-spectrum bulbs. Ozone is a double-edged sword; it neutralizes all manner of microorganism, including ones that are in the shadow of the UVC rays, but it’s also harmful for people to breathe ozone gas.

Some Ultraviolet Light Background

Ultraviolet light is a type of radiation emitted from the sun. It is divided into 3 main categories, A, B, and C based on the light’s wavelength. These categories of light can also be produced by light bulbs. The wavelength is important when purchasing the proper equipment. For our purposes, you want to be sure to purchase products that are in the UVC spectrum, not UVA or UVB. The wavelength of UV light is measured in something called nanometers and is abbreviated as nm.

UVA is the least damaging type of UV radiation. It is the type of UV light that ages our skin. The wavelength of UVA is 315- 400 nm. UVA is not blocked by the atmosphere as it is transmitted by the sun.

UVB light is partially blocked by the atmosphere. UVB light is the type of UV light that causes skin cancer, but also the type of light that our bodies need to make vitamin D. UVB light is used in tanning beds. People who keep reptiles in aquariums are familiar with UVB light, as indoor reptiles need it for their metabolism to stay healthy. The wavelength of UVB is between 280 and 315 nm.

UVC light, the focus of this article, is blocked entirely by the atmosphere on its way from the sun. It is the most dangerous type of UV light.   Life on earth, has little biological defense from UVC, because evolutionarily we were never exposed to it.   The wavelength of UVC light is between 100 and 280 nm, the most effective wavelength of UVC is 254nm. Wavelengths between 100 and 200 nm produce larger amounts of ozone. Try to find bulbs that are close to 254nm.

UVC light is also dangerous to people and animals. Like any powerful tools, it must be used properly. Clothing that blocks the sun, will also block UVC light. Special googles or visors are recommended for eye protection. Conventional eyewear and clear plastic visors, do block some, or maybe even most UVC rays, but I would not depend on them to protect my vision, and recommend specific UVC blocking goggles.

Damage to exposed skin may be slow depending on the part of body exposed and the intensity, but eye damage is very quick and may be long-lasting.   Proper technique and proper protective equipment are essential. Fortunately, it is not complicated or costly to use UVC safely. DO NOT SHINE UVC LIGHT ON UNPROTECTED PEOPLE OR LIVING ANIMALS.

How is UVC used?

UVC light can used the purify air, water, food and hard surfaces. UVC devices can be in ovens, light fixtures, part of air purification systems, wands and certain purpose-built items.

Water – many readers of this blog probably already own a UVC device for disinfecting water. The Steripen and other similar devices found in many bugout/get home bags, uses UVC light to purify water. The bulbs are in a waterproof housing and inserted into the water container for a preset amount of time and turn off when completed. I highly recommend purchasing a UVC water disinfecting device. They are not particularly expensive and work well.

This is good place to discuss a few more characteristics of UVC light

  • It only disinfects what it shines on. Microorganisms in the shadows are not affected. Cloudy water seriously hampers the ability of UVC to completely penetrate through the fluid. Water must be clear for UVC to be effective.
  • It has no effect on chemical contamination. Water treated with UVC may still not be potable due to pesticides and other chemicals.
  • Distance, time and strength. Some microorganisms are neutralized quicker than others and the strength of UVC light falls off with distance (more on this later). The manufacturers of these devices base the run time on the size of the expected container, (The larger the container, the greater distance that the light must travel) and the most likely pathogens in the water. When in doubt, run it twice.
  • The strength of the light is influenced by the voltage of the batteries and the condition of the bulb. If using older batteries or bulbs, exercise caution.
  • Plastics and glass absorb UVC and greatly diminish or stop its transmission, that’s why it’s safe to hold the bottle when running the device. It is possible to use a wand-type UVC device to disinfect an open basin of water by running the wand over the surface and not immersing, but the basin must be fairly shallow and allow for light transmission. Shining a handheld device on the outside of a bottle would not be effective.
  • Over time, UVC will break down plastics and fabrics, the same way sunlight will.

(To be concluded tomorrow, in Part 2.)


  1. Be VERY CAREFUL with UV light — family member used it for various things….Next thing we know this adult family member was blinded for 2 days straight. In so much pain that he was on his back, incapacitated. Unbearable pain.

  2. I tried to buy some of these devices back in March, but I was too slow, they either sold out, or the price doubled or tripled.

    Last week, I had to take a Covid-19 certification test, one of the questions was about UV lights being used to kill Covid-19, I answered yes, but that was the wrong answer. The testers were sourcing their info from, WHO… Apparently, WHO doesn’t want folks using UV because some devices are dangerous, and others with the wrong kind of UV are ineffective.

    I have low confidence in WHO, so I look forward to the next post and recommendations.

    Down South, we have awful issues with mold and mildew, which might be better controlled with UV.

  3. Thanks for the info Doc! We are looking forward to your subsequent article(s).

    We considered purchasing UV for disinfecting water, but short of just throwing money at it wanted to research first, but just didn’t have time with everything else. Fortunately your article confirmed that we needed more info to purchase the proper equipment. Hopefully you will make some recommendations.

  4. Thank you, Dr. David J! An excellent article. We look forward to learning more! In addition to our UV wand, we have been talking about a UVC box, and think we’ll proceed to build one of those since it remains useful during the course of SARS-COV-2 and COVID-19, will be helpful in any kind of more typical flu season coming — and will be in place for use in any future pandemic conditions. We are quite certain that SARS-COV-2 wont’ be the last of viral warfare.

  5. Good Info, Dr. J, but FRAUD ALERT!! Many (most?!!) of the “Germicidal LED” lamps out there are fake! Fortunately, the glass tube ones are excellent!

    I’m a scientist who, like anonymous above, tried to buy these lights early into the pandemic and build disinfection boxes to clean and re-use PPE for my local clinic. Because I had learned that the real LEDs were very expensive ($5-15 each), I suspected the “corn cob” LED-covered (100-150 LEDs) lights being sold online for $30-50 were bogus. So I borrowed a fellow nerd’s Ocean Optics USB4000 $5000 spectrometer. The glass tube lamps, discussed in a moment, are legit but ALL the LED corncob-style lamps are completely bogus!! They only emit a nice turquoise blue but zero germicidal UV-C. If each LED does not have a small metal ring directly around the emitter, it’s not physically capable of generating UV-C wavelengths (the construction and function of LEDs, especially these at the limit of LED short wavelengths, are beyond the scope of my remarks now). Only a few of the LED products seem to have the metal ring and appropriate price (i.e. $10-30 for a single UV-C LED that plugs into a USB in order to clean small items like a phone or keys). Note that the fake LED “germicidal” lights are found on Amazon, eBay, Wish, etc and they all ignored my emails about selling bogus safety products that may lead to infections and worse.

    The GOOD lights are the glass-tube lamps ($20-35), many of which conveniently screw into a standard lamp socket. They emit several specific wavelengths. The important ones are 253.7nm (“254” – well within the 240-300nm germicidal range, altho 265nm is considered best because it is most effective in killing E. coli, the “gold standard in micro cooties”, as is used to test these things), and also a second helpful wavelength of 183.7nm (“184”) which produces ozone. Ozone is, as Dr. J mentioned, irritating to breath but it can be very helpful if confined in a box. Then the ozone kills the cooties that are in shade from the UV-C 254 light!! The small amount of ozone is no big deal but good ventilation is probably wise.

    So, OPERATIONAL ADVICE: Get the older-school glass tube UV-C lights, line a cheap plastic cooler with shiny aluminum foil, place a rack up off the bottom floor so the light can bounce the individual items to be disinfected and mount the light/socket inside. I use an old darkroom timer to zap those bugs for 30-60 seconds (plenty of time with a typical 15-25W lamp). Please note that these bulbs are low pressure mercury vapor lights and should be disposed of safely per local waste standards. Treat them properly, get the job done for real, and do the right thing when it’s time to toss.

    For more info on fake UV-C lamps, check out YouTube’s “bigclivedotcom” videos. Best wishes!

  6. Thanks Doc, good info. And I hope folks picked up on disease being the main problem long term. Taking care of human waste properly will prevent a lot of disease. Along with clean water.

  7. I bought one of these wands from Costco back when SARS was an issue. Didn’t use it for years until Covid came along. I had to get a new battery for it as the original one no longer took a charge. The company didn’t have any parts available by this time. Went to Batteries Plus and they made me up one for $17. Been using it ever since on everything I bring home from town. I don’t have any evidence that it works other than I’m still Covid free. Too bad Costco doesn’t carry them now???? The company is called Verilux. It is a CleanWave Sanitizing UV-C sanitizing Wand. I have no affiliation with them. Their Ph# is 1-888-544 4865. They did contact me back when they had supplies a couple months ago.

  8. Many of the “Germicidal” LED lights sold online are fake and incapable of emitting proper UV-C wavelengths! The old-school, glass tube (low pressure mercury vapor) lights ARE legit and very effective! Line an old plastic cooler with aluminum foil, put in a rack/grate to allow light all around your PPE etc items, and expose for 30-60 seconds. You can disinfect an entire room with these LP Hg Lamps but don’t expose yourself, pets, plants or photos/artwork to the UV-C.

  9. We had a UV light installed on our furnace to clean the air in the spring. You can adjust the level so there is no ozone smell. I have lung problems, since the install, they are a lot less. If the furnace is on, either for heat or AC it’s doing its job. It claims to remove viruses and bacteria.

  10. Yes, do be careful, short wave UV can blind you! I’m a Gemologist and we use both long wave and short wave UV in gem identification. While I was attending The Gemological Institute of America (way back in 1972) we had a lab tech (that should have known better) go blind for nearly a week! Very painful as stated before.

    Looking forward to your 2nd installment.

  11. A few months ago I bought about four of the glass tube UVC bulbs from a reputable company. They are I think something like 8-11Watt fluorescent bulbs.
    I had to also get a starting switch, and a transformer, the proper fluorescent fixture attachment.
    I’ve also been working on a circuit that would turn the light off attached to a motion sensor. I think the darkroom timer is a good idea.

    For the most part, the virus wouldn’t be in your household unless you bring it with you. But the lamps are useful for other things, and there is a good argument for use in public restrooms if you can prevent exposure to people.

    @Jonathan.Gardner I have a couple of videos of the electric boards I’ve been working on to control these bulbs.(please note, I haven’t paired an actual fluorescent bulb for safety reasons yet).

    Eventually I’ll have a logic board built which will make it much safer to run these bulbs. (I’m thinking a decontamination room concept would be cool).

  12. Technically, the term ‘sterilize’ has more than one definition. It is true that one of the meanings is to exterminate all micro-organisms. Rendering micro-organisms to be unable to reproduce is also a proper definition of the word. Virii are not ‘living’ organisms, so theoretically can’t be killed. Their molecular structures can be damaged by short wavelength UV as well as heat, gamma radiation, etc. My recommendation is to purchase lamps of a known specific wavelength from a reputable dealer (stay away from eBay and Amazon on this one). Geo-Guy is correct that 240-300nm is the sweet spot for this application. You can purchase safety glasses designed specifically for the wavelength spectrum that matches your lamp for a reasonable sum. Please do NOT rely on sunglasses ‘rated for UV’.

    I enjoyed reading the article.

Comments are closed.