A germicidal light bulb is used as a highly effective disinfectant as it emits a UVC type light which disrupts the DNA or RNA of microorganisms.   This light is classed as a type of ultraviolet light and unlike UVA and UVB rays that come from the sun UVC light is mostly filtered out by the earth's atmosphere.  It needs to be used in a controlled indoor environment as it is harmful to human eyesight.

The mechanism used in these lights is called ultraviolet germicidal irradiation (UVGI). When the UV-C light penetrates a microbe it does photochemical damage to the nucleic acids within the virus, bacteria etc. damaging the DNA/RNA. This damage prevents it from reproducing and neutralizes which prevents infection or contamination being spread.  

Germicidal lights are used extensively in clinical, laboratory, and industrial settings, such as hospitals and water treatment plants where sanitation is critical.   

Do Germicidal Light Bulbs Work At Getting Rid of Microbes?

Yes and this is backed by decades of scientific research and practical application.  It is important however to make sure that you are using them in the correct application and dosage for what you need.

For the UVC light to work, microorganisms have to be exposed to a sufficient dose of the radiation.  Direct exposure is crucial to make this work as UVC light will only disinfect surfaces that it is directly illuminating.  If there are any shadows or objects covering the area you are trying to disinfect the light will not work. You will also need a light that has a wavelength of around 265nm as this is when they are the most effective at disrupting the DNA in the microbes you are looking to eradicate.  

When correctly installed and taken care of germicidal light bulbs are highly effective at reducing airborne pathogens which leads to reduced surface contamination, and bio-film growth that can occur in water and air care systems.

How Effective is Germicidal Light at Killing Mold?

Germicidal UVC light is effective at killing mold and fungal spores, but it will require careful consideration before using it in this way. 

Mold growth is a complex issue involving moisture, organic materials, and poor ventilation. If you are planning to use UVC light to reduce mold is important to note the below:

• Inactivation of Spores: Mold spores which are the main source of the growth of mold can be easily reduced with UVC light. This will help with air quality, as it reduces the number of airborne mold particles in the air.
• Killing Surface Mold: For mold growth that is visible on surfaces such as a wall, UV-C light can kill the exposed surface layer of the mold but it will not be able to penetrate deeply into porous materials.  If the mold has deeply embedded roots in the surface you are treating  you will need separate treatment for this as the mold may regrow once the light has been turned off. 
• Preventive Use (HVAC): One of the most effective tools to use against mold is a HVAC system.  Lamps installed near the cooling coils and drain pans work continuously to suppress the growth of mold and mildew that thrive in these moist environments. 

UVC light can be used as a control measure for mold particularly for airborne particles but it is not a suitable substitute to get rid of mold in larger established sources of mold in porous surfaces.  

Is It Bad to Have Germicidal Lights in Your Room?

Germicidal UVC lights are particularly harmful to human eyesight and are unsafe to use in a room where people are present. 

The same high-energy UV-C radiation that effectively destroys microbial DNA can also damage human and animal cells. Direct, unprotected exposure can lead to the below health risks:

• Eye Damage: Even brief exposure to direct UVC light can cause photokeratitis which is a painful inflammation of the cornea and is sometimes described as severe sunburn of the eye. Repeated exposure can consequently lead to cataracts and other eye disorders.
• Skin Damage: UVC light can cause severe skin redness and burning and chronic exposure over time can even lead to a risk of skin cancer and accelerated aging. 

Safe Applications in Occupied Spaces:

Whilst we have established that UVC lamps (emitting at 254 nm) are hazardous, there are safe ways to utilize this technology indoors.  Upper-Room UVGI for example uses UVC lamps which are mounted high on walls or ceilings, shining the light parallel to the ceiling.  It is important to make sure they are placed 7 feet or above as airborne pathogens rise and this will help to protect the people below from direct exposure. 

Consumers should always exercise extreme caution when using any germicidal UVC product.   You should never use a traditional UVC lamp in an occupied room where people could come into contact with it. Any residential product claiming to use UV-C rays for disinfection must include with it rigorous safety features, such as automatic shut-offs when motion is detected, to ensure there is no direct human exposure.