The distance from a light source to a target surface is a critical factor in determining the time required to achieve desired UV dosages. The dosage of light delivered follows the inverse square law, meaning the germicidal efficacy of UVC light falls off exponentially as the light source is positioned further from the target surface. For example, a light that is three times as far away will require roughly nine times the exposure time to deliver an equivalent dosage. Stationary UV systems are typically positioned in one area of the room per ‘cycle,’ and standard operation calls for multiple cycles – each one typically five to 15 minutes long. Multiple cycles and positions are recommended to allow for increased UV doses, but these operational principles alone cannot overcome the exponential decay of UVC effectiveness over distance.
UV exposure has been shown to cause discoloration of some target surfaces. The cause of surface discoloration is repeated and lengthy cycle times, which are necessary when stationary light sources target faraway surfaces. Stationary UV systems are calibrated to operate cycles long enough to deliver desired dosages to the targets which are furthest away, but this method leads to those systems delivering doses greater than is necessary to nearby targets. Over time, the treated surface materials may change noticeably.
Thanks to its targeted surface-by-surface application, Dimer’s UVHammer delivers required proven dosages every time and consistently across each surface. In addition to reducing time requirements, minimizing distance and reducing cycle times prevents the likelihood of over-saturating – and potentially damaging – any target surface.
Angle of Incidence & Canyon Wall Effect
Even the smoothest of surfaces feature microscopic divots. This texture provides pathogens with ‘hiding’ places from a fixed UV light source by shadowing the pathogens from the lamp’s line of sight. This phenomenon, known as the ‘canyon wall effect’, was first discovered by Dimer’s very own Dr. Kreitenberg.
Surfaces like floors, chairs or countertops will always be covered in these microscopic textures. It is therefore particularly important to understand the canyon wall effect in the context of how UV lamp orientation on textured surfaces affects the kill rate of contaminants (see illustration below showing why a vertical UV source is not compatible with effective treatment of horizontal surfaces).
To be most effective, UVC lights must be angled so that the lamps are parallel to the target surface, ensuring perpendicular and complete exposure of all lingering particles. Dimer’s novel intellectual property ensures Dimer products are the only mobile solutions able to achieve this improved functionality. It is worth noting that most high contamination surfaces are horizontal.
According to a Georgia Institute of Technology study (Jaffe, 2020), airborne bacteria are 98% more likely to land on a horizontal rather than a vertical surface.
Line of Sight
The principal limitation of UVC germicidal irradiation is the requirement for direct exposure, or line of sight, between the UVC light source and the target. On a macro scale, problematic shadows are caused by different objects (furniture, curtains, IV drips, etc) intercepting the path of the light from the source to target. On a microscopic scale, these micro-shadows are caused by the microscopic divots in material textures. In both cases, a moveable and adjustable UVC lamp is necessary to ensure all target areas are directly exposed to UVC light.
In a 50m² operating room setting, a traditional UVC system would require a five-minute to 15-minute cycle in at least three locations, while furniture and other items are rearranged between cycles in an attempt to reduce shadowed surfaces.
Dimer’s mobility is multidimensional compared to first-generation UVC solutions. An adjustable wing extends from a mobile base, operated at a walking pace to quickly deliver proven germicidal dosages to every surface in any environment. A Nationally Recognized Testing Laboratory (NRTL) has proven Dimer’s ability to disinfect a 400 ft² operating room in less than 3 minutes.