The human eye can see objects due to reflected light in the visual light spectrum. Light behaves like a wave, which has different properties that cause the light to manifest itself in different ways, one of them being wavelength (see image below).
Granted, waves of light do not just exist to help us see. Light acts as a way of transporting energy, meaning that lighting is constantly operating around us, despite us not being able to see it. Some examples of this include x-rays used in a doctor’s office and infrared light used for night vision and thermal imaging.
For most people this visual light ranges from about 380 to 740 nanometers. Nanometers is the scale to which electromagnetic radiation is measured similar to the way that Fahrenheit measures temperature. There are seven color wavelengths within the 380 to 740 spectrums; in descending order they are red, orange, yellow green, blue, indigo and violet. Below the human visual level of 380 nanometers is the ultra violet or UV wavelength. Not all light is safe, ultraviolet (or UV) light being one of them.
Most people have heard of UV light, having been warned about its connection to sunburns, tanning, and overexposure to sunlight. They know that the sun gives off UV rays, causing us to tan, but also making us more susceptible to sunburns, wrinkles, leathery skin, and even skin cancer.
Most do not know, however, that UV light can be further categorized into three groups: UV-A, UV-B, and UV-C.
UV-A light exists below the visible spectrum, which is why we cannot see it, and it is also the most abundant type of UV light in the atmosphere, accounting for up to 95%. UV-A light ranges from 315 to 400 nanometers.
Commonly referred to as blacklight, UV-A is the least dangerous and is used more commonly than the other types of UV light. Many of us have seen UV-A in action at malls, night clubs, or art installations, and many restaurants and food processing facilities use UV-A to trap and kill germ-carrying bugs.
While UV-A is relatively safe due to its emission of long(er) wave light, scientists have linked UV-A to skin cancer, as it can penetrate the middle layer of the skin, damaging collagen and promoting skin aging. Most sunscreens only protect against UV-B, so look for products with “broadspectrum protection” on the label.
UV-B includes light of 280 to 315 nanometers. This type of light is what causes us to tan or burn and it is through UV-B that we receive vitamin D from the sun. Tanning salons have capitalized on UV-B, with their tanning beds providing enough UV-B to get a tan in a shorter amount of time.
Similarly to UV-A, UV-B promotes skin aging and the development of skin cancer, working specifically in the superficial layers of the skin. However, unlike UV-A, the atmosphere filters out most UV-B from the sun.
Finally, UV-C includes light of 100 to 280 nanometers. UV-C poses various health risks, but, like UV-B, the atmosphere filters out its radiation. However, because of its highly damaging nature, scientists have found numerous uses for UV-C, including water disinfection and germicidal irradiation.
UV-C is most dangerous to humans at the 253.7 nanometer wavelength and becomes safer at 222 nanometers. Even so, because the radiation from UV-C can cause cancer and cataracts, medical grade personal protective equipment, PPE, and procedures must be handled with the utmost care to avoid its dangerous side effects. The hope is that, in combination with hand washing and facemasks, UV-C light can be used to effectively eradicate COVID-19 and make public spaces safer.
In June Signify announced that Boston University’s National Emerging Infectious Diseases Laboratories (NEIDL) exposed materials containing the virus to a UV-C tube lamp from Signify. It found that a dose of 5 mJ/cm2 resulted in “a reduction of the SARS-CoV-2 virus of 99% in 6 seconds” (SARS-CoV-2 is the more scientific name for the novel coronavirus). Signify provided Boston University with a 35W Philips TUV light source emitting at around 254 nm.
Later that same month, Acuity announced a partnership with Ushio and launched the Care222 lamp module, which emits intermittent pulses of the 222nm UV light to reduce pathogens on surfaces. The lamps are produced by Ushio and feature a specially designed short pass filter, based on research and technology developed by Columbia University, which filters out from the lamp the longer UV wavelengths that are harmful to humans.
Stones River Electric in Nashville recently installed UV-C technology on a job site. In that application the luminaires were mounted high in the ceiling on the short-dimension wall of a room in order to traverse the long dimension and flood the upper room area; no direct view of the light source was possible, with fixed louvers helping to further decrease the direct sight lines to the source. Additionally, Stones River found mixing UV sources was also an effective way to sterilize rooms and treat patients. Using light for disinfection is especially helpful because it is able to bounce and reflect into hard to reach areas of the room that may be passed over when cleaning by hand.
As scientists continue expand their knowledge of UV light, we can anticipate finding more ways to use the different types of UV light for good in spite of their harmful properties.
This article originally appeared in the August 2020 issue of designing lighting.