# General advice of using UV light (UVA, UVB and UVC) The document discusses the practical use of UV light and safety concerns. ### Misconceptions about UV Nowadays, many consumer appliances claim to disinfect or even sterilize objects, rooms, and air. While this is true for certain UV ranges, such as UVC and Far-UVC, UVA and UVB do not have this effect. Many inexpensive devices advertise that they use UVC, but in reality, they often use UVA or UVB lights or LEDs. For a consumer, verifying this is difficult you would need a radiometer or UV dosimeter to test the light and confirm it is truly UVC. Some products that claim to use UVC allow direct exposure of the light in the way the appliance is built. This is dangerous because UVC is highly harmful to humans. Ideally, UVC should only be used in closed containers with no exposure to skin or eyes. If you can see the UV light, this could indicate it is not UVC. If it is real UVC, exposure could cause serious damage to the eyes and skin. ### Advice - When buying an appliance that claims to use UVC, ask for an official lab measurement sheet to verify its wavelength. - For absolute certainty, consider using a radiometer, dosimeter, or UV test strips to check the UV output. - If lights are exposed (if you can see them clearly in the appliance) it probably is not UVC. If it is, you risk serious danger! - Never look at a UVC emitting LED or bulb. UVC is invisible and causes severe damage. ### Possible risks - Remember UVC kills microbes, but when they die they produce endotoxins. See the section below on Effects of UVC Cleaning for more information. - Ozone might be produced in UVC cleaning, which can lead to other health issues. - Skin damage, increasing cancer risk. - Serious irreversible eye damage. # UVC LEDS and Bulbs Be especially careful with appliances containing UVC LEDs. Most UVC LEDs are expensive, ranging from $3–$6 per LED. If a cheap appliance has many UVC LEDs, it might not actually be using UVC. Manufacturing real UVC LEDs is difficult, and many LEDs on the market are not genuine UVC. ``` | Feature | UVC LEDs | UVC Bulbs (Mercury or Low-Pressure) | | -----------------| -------------------------------------------------------------- | -------------------------------------------------------------------- | | Light Source | Solid-state semiconductor | Mercury vapor or gas-discharge | | Wavelength Range | Typically 260–280 nm, precise and tunable | Typically 254 nm (germicidal peak) | | Size | Small, compact, can be integrated into devices | Larger, require fixtures or housings | | Lifespan | 5,000–10,000 hours, sometimes less | 8,000–12,000 hours, more consistent over time | | Warm-up Time | Instant on | May take several minutes to reach full intensity | | Power Efficiency | Less efficient at generating UVC per watt | More efficient for producing UVC | | Heat Output | Minimal | Can get hot, requires cooling | | Applications | Small devices, portable sterilizers, water bottles, HVAC units | Lab sterilizers, large air/water sterilization, surface disinfection | ``` ## UV types misconceptions ``` | UV Type | Common Misconceptions | Clarification | | ----------- | --------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | UVA | "UVA is safe because it doesn't burn the skin." | UVA penetrates deep into the skin and contributes to premature aging, DNA damage, and skin cancer risk. It is not harmless. | | UVB | "Only sunburn is dangerous, UVB doesn't affect deeper tissues." | UVB causes sunburn and directly damages DNA, increasing skin cancer risk. It affects the outer layer of the skin but is very potent biologically. | | UVC | "All UVC is extremely dangerous and should never be used." | Most UVC from the sun is blocked by the atmosphere. Artificial UVC (especially far-UVC, ~222 nm) can be safer for surface disinfection but still requires careful exposure control. | | General | "Tanning beds are safer than sun exposure." | Tanning beds often emit high levels of UVA and UVB, increasing cancer risk. No artificial UV source is completely safe. | | Far-UVC | "Far-UVC is completely harmless." | Far-UVC penetrates less and is less harmful to skin and eyes, but safety limits must still be followed. Long-term effects are still under study. | ``` # Understanding Ultraviolet (UV) Light Ultraviolet (UV) light is part of the electromagnetic spectrum with wavelengths shorter than visible light but longer than X-rays. UV is divided into several ranges, each with unique characteristics, uses, and safety considerations: - UVA (315–400 nm): Long-wave UV, penetrates deep into the skin. Commonly associated with tanning and skin aging. - UVB (280–315 nm): Medium-wave UV, responsible for sunburn and vitamin D synthesis. More energetic than UVA and can cause DNA damage. - UVC (100–280 nm): Short-wave UV, mostly absorbed by the atmosphere. Extremely effective at killing bacteria and viruses (germicidal). Very dangerous for eyes and skin. - Far-UVC (200–230 nm): A sub-range of UVC. Kills microbes effectively while being much safer for human exposure under controlled doses. - Extreme UV (<100 nm): Absorbed by air; used only in specialized lab equipment. Highly dangerous. --- ## UV Range Table ``` | UV Range | Wavelength (nm)| Characteristics| Main Effects / Uses | Typical Germicidal Dose | Safety Notes | Most Effective Against Germs | |-------------|----------------|----------------|---------------------------------------------------|--------------------------|----------------------------------------------------------|------------------------------- | UVA | 315–400 | Long-wave UV | Skin tanning, aging, phototherapy | Not effective | Can penetrate deep into skin, may cause long-term damage | ❌ Low | UVB | 280–315 | Medium-wave UV | Sunburn, vitamin D synthesis, some phototherapy | Not effective | Can damage skin DNA and eyes | ❌ Low | UVC | 100–280 | Short-wave UV | Surface and water disinfection, sterilization | 30–100 mJ/cm² for 99% | Extremely harmful to eyes and skin; avoid direct exposure| ✅ High | Far-UVC | 200–230 | Short-wave UV | Disinfection in occupied spaces | 20–100 mJ/cm² | Safer for skin/eyes under controlled doses | ✅ High | Extreme UV | <100 | Vacuum UV | Specialized laboratory use | Not commonly used | Absorbed by air, extremely hazardous | ❌ Rarely used ``` --- # Effects of UVC Cleaning While UVC is highly effective at inactivating bacteria, viruses, and other microorganisms, there are several secondary effects to be aware of: ## 1. Endotoxins - What they are: Endotoxins are toxins released from the outer membrane of Gram-negative bacteria when the bacteria die. - UVC and endotoxins: Research shows that UVC irradiation can inactivate endotoxins, particularly in water and liquid solutions: - Endotoxin inactivation is proportional to UV dose, with rates around 0.55 endotoxin units/mL per mJ/cm². - First-order kinetics have been observed, with destruction rates of 6–10 minutes for levels up to 100 EU/mL. - Practical applications include maintaining endotoxin levels below 0.125 EU in water distribution systems and sterilizing parenteral solutions. - Caveat: Most studies focus on water or solutions. Endotoxin release on solid surfaces or in air after UVC disinfection is still under-researched and may represent a blind spot in the literature. ### Note on UV and Endotoxin Release in Complex Systems Research indicates that in environments like sewage effluent or reclaimed water, UV disinfection can exacerbate endotoxin release: - Observation: UV or Fe(VI) alone cannot completely eliminate endotoxins and may increase their presence when bacteria are inactivated. - Implication: While UV is effective at killing microorganisms, endotoxin remnants may persist or even increase, especially in complex biological matrices. - Practical takeaway: For environments with high endotoxin load, UV treatment alone may be insufficient. Additional treatment methods may be needed to manage residual endotoxins and reduce inhalation hazards. ## 2. Ozone Production - What it is: Ozone (O₃) is a reactive oxygen species that can form when UVC interacts with oxygen molecules in air. - How it occurs: UVC lamps, especially those emitting wavelengths below ~240 nm, can split O₂ molecules, forming ozone. - Risks: Ozone is toxic to humans, irritating the respiratory system and eyes. High concentrations can cause coughing, shortness of breath, or lung damage. - Mitigation: Proper ventilation or using ozone-free UVC lamps can reduce the risk. Many modern UVC LEDs emit wavelengths above 240 nm and produce little or no ozone. ## 3. Practical Notes - UVC cleaning is most effective in controlled, closed environments. - Surfaces should be wiped or cleaned after UVC exposure if endotoxin removal is necessary. - Ensure proper ventilation if UVC lamps may produce ozone. - Direct exposure to humans is still dangerous, even if ozone and endotoxin risks are managed. --- Key Notes: - Most germicidal effective: UVC (254 nm) is standard in sterilization lamps; Far-UVC (~222 nm) is almost as effective but safer for human exposure. - Germicidal dose is the UV energy required to inactivate 99% of microbes; it depends on wavelength, distance, and exposure time. - Safety first: Even short exposure to 254 nm UVC can severely damage eyes and skin. Far-UVC has limited penetration and is safer under strict limits. # References / Sources 1. Endotoxin Inactivation in Water by Using Medium-Pressure UV Lamps W. B. Anderson, P. Huck, D. Dixon, Colin I. Mayfield *Applied and Environmental Microbiology, 2003* - Found that endotoxin inactivation is proportional to UV dose (~0.55 endotoxin units/mL per mJ/cm²). 2. Negligible Increase in Indoor Endotoxin Activity by 222 nm Far-UVC Illumination on Bioaerosols Zhancong Liang, Tim Yiu Cheung, W. Chan, Chee Kent Lim, A. Lai, et al. *Environmental Science: Atmospheres, 2023* - Far-UVC at 222 nm caused negligible increase in endotoxin activity when disinfecting bioaerosols. 3. Ultraviolet Irradiation to Preserve High Reverse Osmosis Water Quality A. Stragier, M. Jadoul *Clinical Nephrology, 2005* - UV maintained low bacterial and endotoxin levels in reverse osmosis water (<0.125 EU). 4. The Rate of Endotoxin Destruction During Water Treatment Using a Combination of Ozone and Ultraviolet Radiation M. G. Lee, P. Hunt, J. Vallor *Journal of Parenteral Science and Technology, 1991* - Observed first-order kinetics for endotoxin destruction (D-value 6–10 min for up to 100 EU/mL). 5. Aplicación de luz UVC para esterilizar soluciones parenterales Ana Julia Amasino, Mariana Fernández Blanco, Roque Miranda, D. Olivera, F. Cárdenas, et al. *Ciencia Veterinaria, 2018* - UVC radiation effectively sterilized parenteral solutions with 99–100% inactivation, maintaining sterility in refrigerated storage. 6. Assessment of Ultraviolet-C Light for Sterilization of Hysteroscopy Instruments J. A. Mora-Galvan, Luis F. Escobar-Ponce, Andrea Olguín-Ortega, et al. *Cureus, 2024* - UV-C achieved a 96.08% sterilization rate, comparable to conventional methods, with no clinical infections reported.