Ultraviolet (UV) radiation is comprised of the part of the electromagnetic spectrum with wavelengths in the range of 100–400 nm. This band is situated in between ionizing X-rays and visible light in terms of photon energy and is invisible to the human eye. Although, most photon energies in the UV band are not strong enough to ionize materials, except for extreme UV radiation, they can initiate chemical and biochemical reactions.
While UV radiation is a very useful part of the electromagnetic spectrum with applications in lithography, medicine, forensics, and more, UV blocking filters play an important role in photography, in protecting ourselves from harmful radiation and protecting collectibles and artwork from degradation.
UV radiation is categorized into three wavelength bands: UV-A (320–400 nm), UV-B (280–320 nm) and UV-C (100–280 nem), respectively.
Although solar radiation contains all three types of UV bands, the ozone layer mostly absorbs the UV-C band. All three UV bands find useful industrial and medical applications such non-contact disinfectants for viral and bacterial contamination. For human health, UV-A radiation assists in the production of vitamin D, which is essential for our wellbeing. UV-B radiation is used in stimulating wound healing and phototherapy. UV-C is particularly useful for disinfecting dangerous microorganisms such as the novel Coronavirus (2019- nCoV). UV-C wavelengths at 222 and 254 nm have the highest potential to destroy the DNA and RNA of the virus and prevent them from replicating.
Coronovirus UV-C Disinfection
Although UV radiation finds utility in many applications, it has several detrimental effects and is harmful or unwanted in range of applications. For instance, UV radiation causes skin damage, eye damage, accelerates aging, and damages dyes and pigments.. As a result, blocking UV radiation is essential in many products and applications. Just as sunscreen acts as a UV filter and protects our skin, there are ‘optical sunscreens’ or ‘ultraviolet filters’/’UV blocking filters’ for optical applications. In this article, we will discuss how UV blocking filters work and share several interesting applications.
What Are UV Blocking Filters?
As the name suggests, UV blocking filters block ultraviolet light. These filters have very low transmission for UV wavelengths and high transmission for visible wavelengths. This function can be achieved in two ways:
- Using a substrate that naturally absorbs UV radiation, such as acrylics (PMMA). While acrylics do absorb UV radiation, they typically do not have sharp cutoff wavelengths and their spectral properties are challenging to tune.
- Learn more about PMMA from our Optical Material: Plastics blog post.
- Using dichroic coatings to achieve UV blocking function. Dichroic filters offer greater flexibility of spectral properties such as sharp cutoff wavelengths. These dichroic filters are fabricated by evaporating multilayer thin films that transmit visible light and reflect UV light — a process achieved through constructive interference.
EMF’s Optivex™ line of UV blocking filters offer 99% distortion-free UV blocking by combining excellent optical characteristics, color balance, and rugged durability. They are used by museums, galleries and art collectors around the globe to protect rare and expensive art from harmful UV light. These dichroic coatings can be applied to a variety of lenses and optical components. They can also be deposited on borosilicate glass and are by far the best UV blocking filters in terms of color consistency and stability.
Applications of UV Blocking Filters
UV Protective Filters for Eyeglasses
One of the most common applications of UV blocking filters is as eye protection in eyeglasses. Most eyeglasses today have some form of UV blocking filter, which limits harmful UV-A and UV-B radiation that can damage the retina and cornea in our eyes. Dichroic filters coated on eyeglass lenses transmit visible light while blocking UV light. This is evident from the bluish tint seen in eyeglass lenses with UV filters.
Protecting Pigmentation in Art Installations
As mentioned earlier, UV radiation can initiate chemical reactions in dyes and pigments that cause bleaching and fading in paintings and other artwork. Museums and art galleries use a special form of glass called Art Glass to showcase artwork and artifacts. This glass features an optical coating to block UV light that triggers damaging chemical reactions. These special glasses help in the preservation of artwork that would otherwise suffer damage due to UV light. These glasses are also called ‘conservation glass’ or ‘museum glass’ and can either have dichroic coatings or be fabricated with acrylic substrates.
Fluorescence Imaging and Microscopy
UV radiation is also commonly used in exciting fluorophores in dyes or labels that are used routinely in biochemistry, molecular biology, and material science research. In these applications, higher wavelength fluorescence light is of interest and UV filters are used to block and absorb UV light from corrupting the fluorescence signal. Herein, UV pass filters are used in front of a broadband light source (black light), and a long pass filter (UV blocking and visible pass) selectively transmits visible light to a camera or spectrometer for imaging purposes.
UV filters are very common in outdoor photography to minimize haze effects that occur due to proximity to water or snow. Haze imparts a bluish tinge to photographs and decreases clarity. In such cases, UV filters in the UV-A and UV-B bands can significantly improve the quality of photographs.
UV blocking filters are an integral part of applications ranging from imaging, optometry, art preservation and photography. EMF’s Optivex dichroic UV blocking filters block 99% of harmful UV radiation while transmitting high-quality visible light with virtually no distortion. Optivex has been a product of choice for art galleries and museums for over 25 years, and its name is synonymous with absolute UV protection.