Disinfecting with Light

It’s hard to believe (and hard to admit in print) I’ve been in the lighting industry for almost 20 years.  I started as a lighting designer before LEDs were even a thing and it’s rare I get excited anymore about a new lighting technology.  But, when I learned about disinfecting with 405 nanometers (nm) light – I became a passionate advocate. 

Since March of 2020 and the start of the global coronavirus pandemic, I’ve also been reading and listening to everything I can get my hands on about disinfecting with ultraviolet (UV) lighting.   In the past four months, I’ve read countless articles and posts from prominent architects and engineers that suggest part of the “new normal” is using UV lights, specifically, to disinfect your space.  Have you read these articles, too?  Are you asking yourself “Does this even work?  What is possible and is it safe?”

The short answer is “Yes – you can disinfect your space with light.”  Okay.  I’m done.  Have a great weekend. 

What?  You want to dive deeper into what disinfection lighting looks like and how you can employ it in your next design?  Okay…but it’s a much longer answer….

First, there’s a big difference between the two main types of disinfection lighting; UV lighting and visible disinfection lighting.  UV lighting is non-visible light and ranges from 200 to 400 nm.  Visible light disinfection ranges from 400-420 nm, with the peak at 405 nm and has just recently become available with the advancement of LEDs.  See this handy visual I liked from https://www.violetdefense.com/howitworks

Fun Fact

Even though UV light is “invisible,” the light sources that create UV light also have some light emitted in the visible spectrum, so you can see when they are on.

405 nm is a specific wavelength of violet-blue light in the visible spectrum of lighting. It’s safe for humans and has passed all sorts of safety tests.  It’s proven in both laboratory and clinical settings to reduce hospital-associated infections.  405 nm kills bacteria, but there’s evidence that it can also work to inactivate viruses when they are in a biologically-relevant material (saliva, blood, you know, the usual biologically-relevant stuff).  More research is being done – but this means, 405 nm light may have a negative effect on viruses when the viruses are in droplets.  

UV lighting is divided into three types: UVA, UVB, and UVC.  Although UV lighting is emitted in the sun’s rays, only the harmful UV-A and UV-B rays make it to earth’s surface.  The UV-A and UV-B rays are what causes sun damage, skin cancer and sunburns.  UVC is created from artificial light sources like mercury vapor, xenon, excimer lamps and even a few LEDs. 

The most effective type of lighting used to disinfect is UV-C, sometimes known as germicidal UV or GUV.  UV-C has actually been around for more than 100 years and today, it’s commonly used at water filtration plants and inside HVAC units and ductwork.  Hospitals frequently use it for “terminal cleans” at the end of the day in an operating room. 

Fun Fact

Even when you use light to disinfect, you still have to clean!

In 2011, research pioneered by scientists at the University of Strathclyde was awarded the Times Higher Education Research Project of the Year.  The researchers looked at high touch areas of hospital rooms and they were able to prove reduced bacterial contamination by as much as 90 percent with ceiling mounted 405 nm lights.   Lights with this technology became available in the US in 2016 and have since been installed in hundreds of locations.  We even have installations here in Kansas City.  

Up until the 1950’s UVC was commonly used in classrooms and hospitals to disinfect the upper air.  This worked great because most of these spaces had high ceilings, fans and operable windows to move the air..  But a few things happened that led to the decline of UV lighting until recently: design changes to the space made it difficult to use UV for upper air disinfection, the advent of modern antibiotics and the advancement of other disinfectants.

Since the start of the 2020 coronavirus pandemic, we’ve seen a huge resurgence in UV-C products. UV is really good at disinfecting the air, but it has a hard time penetrating into fabrics, through dust and liquids.  UV lighting is absorbed by most materials and doesn’t reflect well.  You’ve probably heard that UVC lighting is harmful to humans and pets and even architectural materials – but I still had to include this warning!  The good news is that UVC lighting can disinfect quickly and the lights don’t have to be on very long at a time.

But before you start specifying “UV-C” lights, there are some warnings that come with the product, the biggest of which is: it can’t be on when people are in the space!  Lighting controls to protect your occupants are required.  They can include occupancy sensors, time clocks and door lock switches. 

UV lights come in a number of different form factors.  Portable “robots”, ceiling mount and task lights are available.  UV lights are going to be installed in addition to the lights you need for your normal activities.  You’ll want to work with a reputable manufacturer to make sure you are getting what you are paying for. The manufacturer will tell you the spacing recommendations for your space based on ceiling height and furniture layout and what pathogens you are trying to kill.  If you’re trying to kill the really nasty stuff, plan on your lights being on longer and your space being unoccupied for longer periods of time.  Most of the products that are available immediately are using mercury vapor lamps, although there are some LED UV products available. 

Fun Fact

Disinfectants can be divided into two categories: continuous and episodic.  With episodic disinfectants, your space is disinfected for a time being – until people walk in the space…nd breathe or cough or sneeze or talk and shed viruses and bacteria.  Continuous disinfectants are constantly disinfecting your space even while people are going about their lives.  Which one is better?  Okay, this was a trick question.  Neither is better.  They both are effective and can even be used together. 

405 nm is able to reflect off of surfaces throughout a space and can kill bacteria in the air, and on hard and soft surfaces anywhere the light is able to reflect to.  The lights need to be on to be disinfecting, but that’s fine – because they are safe.  What I love about the 405 nm disinfection light is that it can be used all the time – even when people are in the space.  It’s easily blended with white LEDs and you can’t even tell it’s on.  It’s going to be continuously killing bacteria throughout the day. Even while people continue to walk in and out and shed bacteria. 

405nm is  in standard overhead lights that come in all  shapes,sizes and outputs.  We are seeing this technology used by more and more lighting manufacturers every day.  Your regular lights used to light your office will also be your disinfection lights.  Do your lighting layout with 405 nm and white blended light and you’re disinfecting. Easy peasyy, right? 

Fun Fact

If you’ve been to the doctor in the last two decades, you know that doctors are hesitate to prescribe antibiotics because of antibiotic resistance.  Bacteria that are resistant to antibiotics are a HUGE concern. Did you know that MRSA stands for “methicillin-resistant Staphylococcus aureus?”  It’s right in the name.  There is no evidence that UV lighting or 405 nm light can make bacteria more resistant to antibiotics or that bacteria will become resistant to the light because of how the light kills bacteria.  More science stuff. 

You might have read a little about Far-UVC (200-225 nm).  In a laboratory setting, it’s proven to deactivate the viruses and kill bacteria, but the IUVA (International Ultraviolet Association – yeah – it’s new to me, too) just released a white paper stating it’s still hasn’t been proven to be safe for humans. 

The only completed research looking at health problems from regular exposure to Far-UVC has been done on mice.  But, the data is looking promising that Far-UVC could be safe for humans.  Stay tuned.  There are no Far-UVC LED sources, yet, either. 

Did you pay attention to that long answer?  Way to go!  I hope you’ve learned a little and if you want to become as passionate about disinfection lighting as I am – that’s wonderful!  We can talk all the time about it.  Because I’m working from home and I have the time.  Let’s talk more!  I’ll call you.  Or you call me.  Or, connect with me on LinkedIn where I post a LOT about it.

To learn more about these topics, please click below:

Proven HAI reduction


Study of 405nm on viral loads


General role of 405nm with infection control



UV’s impact on COVID-19

UV safety


UV history



Far UVC statement


IES and UV

Air disinfection with UV lighting



Water disinfection with UV


UV’s effect on materials


by Autumn Nieland