Does UV Light Kill Mold? (2020 Ultimate Guide)

Do you want to know if ultraviolet light will actually kill mold?

UV radiation has been in use for years by hospitals to disinfect operating rooms and medical equipment.

In this guide, I will be going over...

  • How UV light kills and prevents mold growth
  • The different types of germicidal UV light products to kill mold
  • Why I always recommend installing a UV light in your HVAC system

Let's get started with this guide!

does uv light kill mold

Will UV Light Actually Kill Mold?

Under the right conditions and with a properly designed product, germicidal UV light can be effective in killing mold --- and preventing it from taking root.  UV light has been in use for many years as a disinfecting technology to not only kill mold, but also bacteria, viruses, and other pathogens.  

In fact, as early as 1878, Arthur Downes wrote a scientific paper describing the sterilization of bacteria to short-wavelength light.

Ultraviolet light acts very similarly to humans getting a sunburn. Sunburns are caused by longer wavelength light, but the principle is very much the same. Mold and other microbes have far less protection against the germicidal effects of light than humans.

Read Also: What Are The Signs Of Black Mold In Air Vents?

The UV-C Short Wavelength

Scientists have discovered that there is a certain wavelength range where microorganisms are vulnerable to damage --- and this is the UV-C short wavelength range --- specifically in the 100 to 280 nanometer range.

Ultraviolet light is used in different industries for microbial decontamination such as in hospitals,  water treatment, air purification, and food sanitization.

There have been numerous scientific studies showing that UV-C is effective in killing microogranisms. The short wavelength known as UV-C is responsible for disrupting the nuclei of microorganisms --- which either kills it or prevents it from reproduction.

Read Also: What Are The Best UV Lights For HVAC Systems?

How Does UV Light Kill Mold?

Ultraviolet irradiation works as a disinfectant and uses electromagnetic waves to penetrate through organisms.

The wavelengths are of various sizes --- between 255 and 280nm --- known as the Germicidal UV-C that kills microorganisms. The ultraviolet light irradiates the immediate environment in which it is placed such as in an indoor air conditioner.

And when the germicidal rays come across molds, they penetrate into the nuclei of the molds, damaging the nucleic acids present --- until their the organism becomes disabled. 

According to the research work found in the US National Library of Medicine on Light-Based Anti-Infectives, it was reported that the disinfectant mechanisms of UV light cause actual damage to DNA by changing the arrangement of the molecules.  

When the DNA "arrangement" is changed, it causes defects in the cell reproduction of the mold and it will eventually lead to cell death --- when the cells die, the mold dies.

Read Also: 7 Pictures Of Mold In Air Ducts

does uv light kill mold in hospitals

What Are The Best Conditions For UV Light To Kill Mold?

The effectiveness of UV light in killing mold depends on multiple factors, and some of the most important things are...

#1. Light Intensity

If the UV light is very weak, then it won't be nearly as effective.

Most UV lights installed in HVAC systems have light bulbs in the 8-watt to 16-watt power range.

In fact, these lights are so powerful that they even have sight glasses (peep holes) so you can  verify the UV light is on without directly looking at it. At this level of intensity, exposure can damage your eyes and skin.

Read Also: What Are The Best Honeywell UV Lights For HVAC?

#2. Line of Sight

In order for UV light to work in killing mold, there has to be line-of-site. 

If the mold is growing behind an object, and UV light isn't directly hitting the mold, then the germicidal effects of the light will be largely non-existent.

The light has to actually reach the mold for it to have any type of effect.

This is one reason why you never see mold growing in direct sunlight. Natural sunlight has a weak germicidal effect on microbes.

#3. UV Lamp Debris

If the UV light bulb is coated in dust or debris, it can also greatly lower its reach. This is why periodically cleaning the UV bulb or replacement is so crucial.

A dirty UV bulb can halve the sanitizing power of a new & clean bulb.

Read Also: How To Install An HVAC UV Light?

What Are The Different Types of Mold-Killing UV Lights?

Since ultraviolet light can be so effective in disinfection of environments, different types of products are available to homeowners in order to kill and prevent mold.

Here are a few different types...

HVAC UV Lights

Perhaps the most common germicidal UV product is the HVAC UV Sanitizer. These custom UV lights are installed inside of your indoor air handler, furnace, or heat pump.

My favorite HVAC UV light is made by a company named OdorStop.

This OdorStop UV Light will kill mold, bacteria, viruses --- and even odors. The OdorStop UV Light also comes with cut-out templates, LED indicator lights, foam tape, and they are super easy to install. 

You can view the price of OdorStop UV Lights on Amazon right here.

HVAC UV lights will have usually have one or two UV bulbs, and these UV lights are normally on 24-hours a day inside of your air handler --- killing microbes and mold.

There are even more premium models that will turn on automatically based on whether the A/C or heat has actually turned on. 

This feature can significantly lengthen the life of the ultraviolet light bulb (one of the biggest ongoing expenses is changing the bulbs yearly).

Read Also: 7 Pictures Of Mold In Air Ducts

does uv light kill mold (hvac uv light)

UV Light Water Sterilizer

There are also UV products designed to purify the entire homes water supply.

These systems will kill microbes, germs, and pathogens that are in your water supply that either the municipal system misses or because you are on well water and need disinfection.

These whole water purification systems are installed at the main water supply, usually installed immediately after the main water shutoff.

does uv light kill mold (uv water sterilizer)

UV Light Whole House Water Sterilizer

Portable UV Disinfection Lamps

Another increasingly popular product is the portable disinfection lamp.

These products are designed to be very small and portable and can be used to quickly disinfect pillows, faucets, door knobs, and other small objects. Some of these portable lamps will turn off automatically if it is held upright in order to prevent damage to your eyes.

does uv light kill mold (portable uv disinfection lamp)

Portable UV Lamp Sanitizer

Whole Room UV Germicidal Lamp With Timer

What's The Bottom Line On UV Light Killing Mold?

UV light can be highly effective in killing and controlling mold in either an HVAC system, water supply, or even for food.

Hospitals, food processing centers, and water treatment facilities have been using germicidal UV light for years, and I'm sure UV will continue to be used to sterilize a variety of objects.

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31 thoughts on “Does UV Light Kill Mold? (2020 Ultimate Guide)”

  1. Hey Michelle,

    There are portable UV light sanitizers on the market, you can use these in your bathroom as short term measure, and they are generally in the 25 to 50-watt power range.

    With these portable UV lights, you still don’t want the light exposed to your skin or eyes, and you want to buy one with a timer that will automatically turn on & off.

    The longer term solution though is to have an effective bathroom exhaust fan to remove moisture. Bathroom exhaust fans should be on for at least 20 minutes after each shower.

    If there is mold growing on the caulking, I would try scrubbing the caulking/grout first with a cleaner to see if it can be removed. If not, you may have to re-caulk or re-grout the bathroom.

    Silicone caulking won’t allow mold to grow on it, but if caulking is never cleaned, there can be a thin dirt film on the caulking that allows mold to take root.

    Good luck!

    Reply
  2. We have/had mold in the air handler and coil area of our furnace. A local HVAC company installed an apco uv light kit that supposedly kills mold, viruses, bacteria, etc., along with purifying air and stopping household odors. I would like to understand what actually happens to the mold that exists already within the furnace – does it just die and remain there as a stain? Does it die and get released into the rest of the duct system, hopefully being caught by the filter? Does it get burned away by the uv light? How long does this process take? Do I need to call in an abatement company to clean out my unit? Hoping for some understanding and direction – Thanks so much!

    Reply
    • Hi Sherri,

      If there is existing mold in the air handler, the UV light will kill the mold, and it will turn into a type of “mold dust”. Unfortunately, this mold dust can still by highly allergic. Whenever I do a home inspection, I always recommend cleaning the air handler first of any visible mold, and then installing the UV light to prevent the mold from growing back.

      In addition, a UV light will only kill mold if it has a direct line-of-site to the mold. As you know, a furnace or heat pump has many different areas that make it difficult to reach with light (like the blower fan, evaporator coil, etc.).

      There are UV lights that are designed for air treatment rather than surface treatment. These UV lights are installed at the return side of the air handler, and these tend to be higher quality and more effective than the “surface treatment” UV lights which are installed on the supply side. However, they are also more expensive.

      Anyways, please clean the air handler of all visible mold, this is an important step.

      Good luck!

      Reply
    • Hi Pam,

      Ordinary grow lights do not have any type of anti-microbial effect on plants (at least nothing substantial). There are actually products designed to emit UVC light to sterilize plants. Perhaps the largest company is based in the Netherlands and called CleanLight. One of there products is called the Hobby Unit Crop Protector, check it out here.

      Good luck!

      Reply
    • Hi Arie. My house smells musty. I am guessing that mold and mildew are what cause the musty smell. It is not a humid house. How can I find out the source of the smell and who can help me get rid of it? My house is one story with a basement. The crawlspace is encapsulated.

      Reply
      • Hi Ellen,

        If the musty smell is from mold, the absolute first place I would check is inside your HVAC air handler or furnace. You can remove the cover and thoroughly inspect inside for mold including the blower fan and around the evaporator coil. This is by far the most common place for mold and musty smells to be coming from.

        After checking the furnace, I would take a peek inside the crawlspace just to make sure there isn’t mold on the joists.

        If you find mold, you can contact a mold remediation company (air duct cleaning companies if its an HVAC problem). To get rid of any residual smell, I would have the air ducts and furnace cleaned by an air duct cleaning company, and then install an HVAC UV light.

        I recommend OdorStop UV lights, you can see them here on Amazon.

        Good luck!

        Reply
  3. Hello there, my parents live on a fix income. They live in a mobile home that I am sure has black mold. The roof leaks and dripping rain is caught by pans in a few parts of the house. My father almost lost his life do to a fungus infection. Possibly valley fever. We live in the valley of California. He’s in the last stage of lung disease. I need molds spores fungus and viruses and bacteria to be killed. I am about to go buy a uvc 40w light off ebay. Should I buy a stronger one? I think I found a 60w uvc light. They create ozone. Dont think I need ozone. I just need to kill these living things before they kill my dad. Thank you

    Reply
    • Hello Teresa,

      Sorry to hear about what’s happening with your parents home and your Dads health.

      If the UVC light creates ozone, that isn’t a problem, as long as you air out the home after use — you don’t want to breathe in ozone, it can be hazardous.

      In fact, there are ozone generators made to kill mold such as the OdorStop OS3500UV Ozone Generator.

      Generally, the higher the wattage, the more powerful the UVC, but 40-watt may be fine. I am not really familiar with mobile homes, I have never inspected them. I would definitely look into the ventilation system and see if there is any fungal growth there. I would also buy a cheap humidistat that will tell you the relative humidity of the mobile home.

      I would also focus on the basics, such as fixing the leaks, cleaning any visible mold, and making sure the indoor humidity stays within 30% to 50% all day long as recommended by the CDC. Buy a dehumidifier if necessary. Mold requires moisture for it to grow.

      What I did recently for my bedroom is buy a 20-inch box fan for $19, and then I taped a 20-inch x 20-inch HVAC filter to it (arrow pointing in direction of air flow). That also can really help with the indoor air quality. Just change the filter every few weeks.

      Good luck!

      Reply
  4. Clothes closet is near the bathroom with an exhaust fan. Mold gets on shoes etc. What wattage of a UV bulb should I use for inside closet.

    Reply
    • Hi Betty,

      Just for a small closet, anything in the 20 to 40 watt range should be fine. I would recommend buying one with a timer. You don’t want UV-C light on your skin or eyes — please be careful.

      Also, the real problem is excess moisture in that area from the bathroom. According to HVI, bathroom fans should be left on at least 20-min after showers. Replacing your wall switch for one that includes a timer is highly recommended, here is one on Amazon made by GE.

      There are also bathroom fans with humidity sensors that will turn on/off automatically. Here is my article on that; Best Bathroom Fans With Humidity Sensors.

      Good luck!

      Reply
  5. I had black mold in my utility closet which is next to my bathroom, which has a window but no exhaust fan. I totally changed drywall, and repaired, however, I am petrified it will come back. So I bought the following light: BOAITE UV Germicidal Lamp UVC with Ozone Light Bulb E26 25w 110v Cleans Air
    However, I read that Ozone could hurt your lungs, was this the right purchase, and if so, how long should I keep it on, because it really smells weird after one minute. PLEASE HELP, I am really afraid my lungs will be damaged with this Ozone light and is killing me instead of the mold!.

    Reply
    • Hi Vivien,

      Ozone can be effective in removing odor and killing mold but it is detrimental to your lungs. Most manufacturers recommend letting the room air out for 30-60min before reusing that area — or at least wait until all of the ozone smell is gone.

      I can’t really say whether it was the right purchase, but the true cause of the mold is the excess moisture from the bathroom. You really need to install a bathroom exhaust fan which all modern bathrooms have. In fact, you are supposed to use the fan during any shower and 20-30min after each shower to remove moisture. Mold requires moisture to grow.

      Windows just don’t really cut it. Depending on where you live, the outdoor air can also contain excessive humidity if you just open a window.

      I would also buy a cheap humidistat (~$10) and monitor the humidity of your closet. Ideally, the humidity shouldn’t go above 60% but between 30% and 50% is what you should shoot for.

      Good luck!

      Reply
  6. Hi,

    My parents have a place in Florida that they use only in the winter season. They’ve had issue with mold growth during the summer season when not there these past two years. I am wondering if I put lights in the closet and close some of the vents in the different rooms would this help. The kitchen was particularly bad this year. I believe the air conditioner turned off completely and we were unaware. I would appreciate any suggestions to help make their place mold proof for when my mother returns. Thank you.

    Reply
    • Hi Robin,

      That is unfortunate to hear about your parents place; mold can be a terrible experience.

      You could install UV lights in the areas of mold growth, such as the closet as you mentioned — it definitely won’t hurt — and it doesn’t use a lot of energy. However, the real cause of mold growth is the excess moisture. If you keep the moisture levels down, it is impossible for mold to grow. The EPA recommends shooting for 30% to 50% for indoor relative humidity.

      Personally, I would install a dehumidifier with a hose to a drain. This way it will drain automatically. I would probably also install a WIFI connected water alarm that you can place on the floor (just in case). In addition, I would want to monitor the air conditioner and humidity levels remotely. You can do this by installing a smart (internet connected) thermostat so you can be alerted if the AC fails or if the humidity level skyrockets.

      Good luck!

      Reply
  7. Hello. I have allergies and asthma. My boyfriend has COPD. What type, brand of UV-C would you recommend. Hand held for now. Later whole condo unit?

    Reply
    • Hi Shelley,

      Sorry to hear about the health issues. I am not very familiar with portable UVC lights TBH, but just be careful to avoid getting the UV light on your skin or eyes. The larger portable units even have timers so that they automatically shutoff. Also, be careful of any portable UVC light that creates ozone, which can be hazardous to your lungs. If it creates ozone, you must air out the room before entering — there should be no more ozone smell.

      For HVAC lights, I really like OdorStop, but Honeywell also makes some good UV lights. Unfortunately, due to what’s going on in the world, most of the UV lights are out of stock. My article on the best HVAC UV lights can be found here.

      I would also stay on top of changing your HVAC filter regularly, like every 3-4 weeks. Get one that is pleated, and designed for allergy sufferers. I just wrote a product review article on this topic of the best air conditioner filters for allergies.

      I am also highly sensitive to allergens and poor air quality, and if I don’t change my filter every 30 days, I really start to feel terrible.

      Good luck!

      Reply
  8. Hi,

    I live in a a very humid city and my loft has only one window. I have been struggling with the humidity and trying to keep the mold under control but its getting a bit ridiculous. I’m looking into different ways to manage it all aside from trying to air out the apt (opening the one window isn’t helpful bc of the humid weather) and cleaning the mold.

    My ac unit has a dehumidifying feature but I am not sure that is enough. What would you recommend I do?

    Reply
    • Hi Tania,

      I do not know where exactly your mold is growing but here are few things I would do. First off, I would buy a simple humidistat for $10, this will tell you the relative humidity in your home. The EPA recommends keeping the humidity between 30-50% to stop mold growth. Then, I would purchase a stand alone dehumidifier since the A/C may not be enough. You can even install a tube into the dehumidifier so it will automatically drain to a sink or something and it will turn on automatically when the humidity rises above a set level. Also, I would make sure to turn on the bathroom exhaust fan at least 30-min after each shower. I have learned that many people are poor at using bathroom fans for whatever reason.

      Good luck!

      Reply
  9. I see compact fluorescent bulbs advertised to kill mold. Sanibulb ionic. They also claim to clean the air in general. Do these work when ceiling mounted and mold may be on the floor 8 feet away? Also are they safe to have on a lot as the regular bathroom light?

    Reply
    • It looks like just a regular incandescent bulb to me. It doesn’t even state that it uses UVC light. Plus, UV light strong enough to kill microbes would be hazardous to your skin and eyes which is why they use timers such as this one by Germicidal UV Lamp By Coospider on Amazon. With any ozone emitting products, you don’t want to breathe it in — very bad for the lungs.

      Stay away is my recommendation — people trying to cash in on the craziness.

      Good luck!

      Reply
    • Hi Jim,

      Yes, you can use a UV light in the basement if you keep any humans and pets away from it. Legit UV lights will have timers in order to automatically turn off. You don’t want UV on you because it can quickly damage your skin and eyes. Also be aware that some create ozone which is harmful if breathed in, air out the room of all ozone smell afterwards with those products.

      Good luck!

      Reply
    • Hi G. Allen,

      I don’t think so. It appears to be for special effects, inspecting stains, and other uses. UV light for killing mold is known as UV-C and has a specific wavelength for killing microbes.

      Arie

      Reply
  10. Hello Arie,
    I had mold remediation in my attic after a tenant filled it with blown in insulation and removed the air vents! Post-remediation, there was a leak in the attic vent which caused mold to appear on the plywood. Handyman washed it off with vinegar, and fixed leak. Question: If I were to put an UV light in the attic, would it be a fire hazard if it fell over on the exposed fiberglass insulation? (There is no hard floor.) Also, do some run on battery, as there is no electrical outlet up there, and I’d have to otherwise run an extension cord through the trap door downstairs. This house has no air vents, as it is on electric heat. Thank you!

    Reply
    • Hi Claire,

      There are portable UV lights on the market, but I am not aware of any that are battery powered. Also, the HVAC UV lights aren’t meant to be used in the attic. Personally, I would re-install the attic vents or just install an attic fan. A UV light would only be a temporary solution anyways.

      Good luck!
      Arie

      Reply
  11. We recently moved to Florida from an extremely dry state. We have a few classic cars that are kept in my insulate, non-conditioned shop. Despite moving the air with fans, mold is growing on the cars interior. Is there a system I can put together and hang from the roof interior of each car? I’m trying to avoid the expense of running an ac in the shop.

    Reply
    • Hey Robert,

      I personally would just install one or two dehumidifiers and have their drain hoses attached to a sink or to the outside (so they can automatically drain & turn on/off). I would also install a humidistat ($10) so you can monitor the humidity. You could install portable disinfectant UV lights, and have them hang from the roof, but they can be hazardous to your vision and skin. They do come with timers but you have to be careful. I think just installing some dehumidifiers is cheaper, easier, and safer though.

      Good luck!

      Arie

      Reply

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Arie Van Tuijl

Arie Van Tuijl

Arie is the founder of Home Inspector Secrets, an online resource dedicated to helping people understand how homes work. He is a licensed home inspector in two U.S states and owns a residential and commercial inspection company (read his full bio on the About page). To ask Arie a question, please use the comment box at the bottom of the relevant article.

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Home Inspector Secrets is an online resource for owners, buyers, and sellers to understand all aspects of home maintenance. We have detailed home guides, product reviews, inspection advice, and much more.