Q&A: Factors Affecting Healthcare Surface Disinfection Efficacy

Compiled and edited by Amy Hedrick, CEO, Cleanbox Technology, Inc.

Note from UV Solutions Editor Dianna Brodine: This Q&A is an excerpt from a more intensive white paper from Cleanbox Technology, Inc. The white paper provides in-depth discussions of UV-C for surface decontamination, including historical relevancy, definitions and measurements, testing procedures and surface degradation impact on plastics, polymers, glass and lenses. A link to the full white paper is provided at the end of this article.

The most commonly known cleaning processes for most commercial and consumer facing products is liquid-based. This means surfaces either need to be sprayed or wiped down with a disinfectant product and then left wet and allowed to dry naturally, which takes two to four minutes or longer. The process of alcohol or other liquid surface decontamination may be adequate for a smooth, flat surface, but the introduction of any edges, pockets or change in surface texture (as with soft or mixed materials) creates an opportunity for missing an area where contaminants exist. In hospital settings, the number of electronic devices (such as mobile phones, keyboards, etc.) have enough hard-to-reach surface space that traditional liquid disinfectants either can’t fully reach all areas or, if they can, potentially may harm the device. This is a problem for many portable electronic and other devices that can go from room to room and potentially transmit disease.

Traditionally, a hospital, industrial, government or business setting requires a higher level of these chemical disinfectants than a consumer product to treat a wide range of bacterial, viral and fungal agents, and with the global impact of COVID-19, there became a growing awareness of the need for medical-grade disinfectant materials in multiple business and consumer settings. While supply chains now are able to provide these higher grades in a more efficient way, the potential impact on consumers is troubling. Given the intense levels of disinfectant, the risk of chemical exposure in both adults and children is rising and likely will result in unintended health issues.

From a commercial standpoint, the impact of COVID-19 on policy and procedures has been damaging. With an increased focus from both regulatory and consumer audiences, the visibility of appropriate hygiene is at the forefront. Because there is so much scrutiny around cleaning protocols, companies now must visually disinfect with traditional cleaning products, often requiring an extended amount of time for the liquid product to dry naturally to complete the cleaning process. This extra time dramatically has reduced productivity and, with traditional cleaning methods, only so much time can be recaptured.4

Ultraviolet rays, specifically the C wavelength of ultraviolet light (UV-C), sanitize and clean more thoroughly and more quickly than other cleaning methods.3 [There are factors that can affect the efficacy of UV-C, and these should be at the forefront when planning for UV-C disinfection.]

What factors impact UV-C efficacy?

1. Line of sight
UV-C is line-of-sight only. If the light can’t shine directly on a pathogen, then it can’t break it down and that pathogen still is able to replicate. UV-C also is a very short wavelength that can be blocked by most materials, including glass and acrylic, and UV-C also is blocked by layers of dead skin cells. However, there are some materials that allow UV-C pass through.

2. Shadowing
Anything blocking light limits the effects of UV-C decontamination. Thus, avoiding shadows is a must in any device that uses UV-C light for disinfection.

The most common shadow-creating component seen in many UV-C devices is a wire rack. An object to disinfect is laid on a rack and the lights are turned on. This means that every place where the rack blocks the light, there is the potential for pathogens to be completely untouched by UV-C light, and contaminants are not eradicated.

Frequently there will need to be a touch point on the device being cleaned to hold it in place. For appropriate decontamination, the touch point(s) should be few and should be in a location that is the least likely to be a contagion point. Again, there are some materials that allow UV-C pass through, but aluminum and metals are not such materials. Properly engineered lighting must be utilized to address this critical issue.

3. Surface
It is easier to eradicate contagions on a flat, non-porous surface than on porous, mixed material or uneven surfaces. The more nuanced a surface, the more opportunity for shadows or spaces in which contagions can hide and grow. Hard and flat surfaces create a different environment for contagions than do soft, porous, textile or other inconsistent surface schematics. Surfaces must be taken into account because they directly impact the level of efficacy that can be achieved using UV-C light. For example, a hard, flat surface leaves less room for contagions to gather vs. surfaces with height or depth differences.²

Again, properly engineered lighting – taking surface schematics and shadowing into account – is a vital consideration for UV-C light to disinfect optimally.

4. Distance
Because of the inverse square law of light, it is important to understand and measure the amount and intensity of UV-C light that is reaching the intended surface. Several factors will impact distance and efficacy, including intensity and duration of UV-C exposure. These observations indicate that proximity to the item being contaminated has a significant impact in cycle time required for targeted levels of decontamination.

5. Duration of Exposure
Low-intensity lights can be safer for use and reduce the possibility of causing damage to the materials being disinfected. However, with lower intensity, longer exposure is required to ensure the same rate of pathogen reduction. This exposure may lead to the degradation of material and/or yellowing of clear materials over time. The higher intensity, the shorter the decontamination cycle time can be. There definitely is a sweet spot in the middle where intensity is high enough to get the job done in the least amount of time and low enough that it would take years of exposure before materials would be damaged.

NOTE: A big box with intense lights on the edges is problematic. Objects close to the lights receive greater and potentially damaging levels of exposure to UV-C than objects in the center.

[See more on UV-C and materials in the full white paper to understand how to use UV-C without risk of damage to sensitive materials, including plastics.]¹

6. Intensity
Because distance is a critical component of light intensity, it is important that any materials to be disinfected are positioned at an optimal distance from the lights, and that materials placed within the disinfecting device receive consistent intensities on all surfaces being treated. Failure to factor this may result in intensities that are too high (which can cause material breakdown and damage) or intensities that are too low (preventing effective disinfection).¹

7. Reflectivity
Many UV-C boxes purporting to provide hygienic solutions are “big box with lights on the edges and reflective surfaces inside.” Reflectivity can be a useful tool when distances are relatively short. In large boxes, reflectivity effectiveness drops off dramatically with each reflective bounce. Each bounce back of the light means the light has traveled a longer distance. UV-C light intensity, and therefore decontamination effectiveness, plummets sharply with each bounce. The intensity of reflected light becomes low so quickly that those reflections have little impact and do not compensate for shadows in a meaningful way.

There are a large variety of reflective surfaces, which vary in effectiveness. Mirrors are one of the least effective reflective surfaces because they reflect the light too precisely. Other materials (like aluminum) bounce light in a more distributed pattern, which makes them more likely to fill an area with light, making them more useful. The trade-off often is evaluating how much light the reflective surface actually absorbs and finding a material that reflects all or most of the light while dispersing it outward in all directions. These reflective materials do exist, but because of their cost, most UV-C devices currently on the market do not utilize them.

Non-precise application of reflectivity for UV-C decontamination applications generally is ineffective. However, reflectivity can be used to great purpose with a) short distances, and; b) the correct reflective materials.¹

What are the critical factors when choosing UV-C decontamination devices?

Not all UV-C is equal. Mercury bulbs are more readily available than LEDs but emit heat and operate at 254 nm. LEDs can operate at higher nm ranges, such as 265 nm to 280 nm, without heat or mercury, but are more expensive. Far UV-C is promising for efficacy but operates at a nanometer range that emits ozone. Consider the sensitivity of the product being decontaminated. Determine if heat, ozone, mercury or other toxins are acceptable for the environment. Finally, consider how simple the operation of the decontamination device needs to be. User-friendly hygienic solutions are important. Ease of use and quick, effective results are key components to consider.


  1. David Georgeson, CTO and co-founder, Cleanbox Technology
  2. Amy Hedrick, CEO and co-founder, Cleanbox Technology
  3. Hoag Memorial Hospital, Newport Beach California
  4. Crystal IS

Contributions by: Hoag Memorial Hospital, Newport Beach California; Dr. Matthew Hardwick, president and CEO, ResInnova Laboratories; Dr. Robert Louis, FAANS, Head of Neurological Surgery at Hoag Memorial Hospital, Empower 360 Endowed Chair for Skull Base and Minimally Invasive Neurosurgery at Pickup Family Neurosciences Institute; Crystal IS, (manufacturer of Klaran UV-C LEDs), an Asahi Kasai Company; Amy Hedrick, CEO, Cleanbox Technology, Inc.; David Georgeson, CTO, Cleanbox Technology, Inc.

To access the full white paper, visit www.cleanboxtech.com.