Ultraviolet light, also known as UV light, is a form of energy traveling through space. It is a form of electromagnetic radiation with a wavelength shorter (100 - 400 nanometers) than that of visible light (400- 780nanometers), meaning that UV light is more energetic.

Light Spectrum. Image Credit: Kellowin

The electromagnetic spectrum is a range of frequencies for electromagnetic radiation. It includes light waves from gamma rays to radio waves. Each carries energy and moves at the speed of light. As the following diagram shows, the energy of the wave increases as the wavelengths become shorter.

How UV Light Works

UV light is produced by the Sun and by some man-made lamps. Although there are many applications for UV light, there is also risk to its use. UV rays have too much energy and can cause molecules to shake until they lose electrons. The loss of an electron can change the chemical structure and cause cell damage by mutating its genetic code.

When radiation is absorbed by matter, either excitation or ionization can occur. Excitation occurs when radiation is excited by the motion of the atoms or molecules, or causes an electron to jump from an occupied orbital into an empty, higher-energy orbital. Ionization occurs when there is enough energy to remove an electron from an atom.

Types of UV Radiation

UV light can be classified as non-ionizing or ionizing radiation.

• Non-ionizing electromagnetic radiation has less energy than the ionization of water (1216 kJ/mole), which is not enough energy to remove an electron. Examples of non- ionizing radiation include visible light, microwaves, and radio waves.
• Ionizing electromagnetic radiation carries more than 1216 kL/mol and can remove an electron from an atom or molecule to produce a chemically reactive free radical. Ionizing radiation is used for X-rays, medical, biological and sterilization applications and is a by-product of nuclear power.

UV Bands

UV light can be further divided into bands. The following chart provides an abridged view of the electromagnetic spectrum and divides UV light into these spectral subcategories.

Chart Credit: Spacewx.com

UV light systems produce ultraviolet radiation falling into one to three major bands:

• Ultraviolet A (UVA) is the long wave UV band (315 to 400 nm). Also known as black light, UVA rays comprise 98% of the ultraviolet in sunlight at the Earth's surface. The rays are present during all daylight hours and are able to penetrate clouds and glass. UVA can cause damage to collagen by destroying vitamin A and causing damage to keratinocytes. Despite its link to skin cancer, UVA rays are frequently used in tanning booths and sun lamps.
• Ultraviolet B (UVB) is the middle UV band (280 to 315 nm). UVB is more energetic than UVA, and is partially absorbed by the ozone layer. These rays are the main cause of skin reddening and skin burns. They damage the skin's superficial epidermis layers and play a key role in the development of skin cancer. UVB intensity varies by season, time of day, and location.
• Ultraviolet C (UVC) is the short wave UV band (100 to 280 nm). UVC rays have the highest energy per photon, and thus are more dangerous than UVA and UVB radiation. They rays are completely absorbed by the ozone layer, but can pose a serious threat if looked at for an extended period of time.

UV Light Ozone Penetration. Image Credit: The Open University

The UVA, UVB, and UVC bands can be further divided into subtypes that denote specific applications and identify the principal absorber of the radiation. These include vacuum and extreme UV rays as seen on the chart above.

Selection Criteria

In addition to type, the Engineering360 SpecSearch database allows industrial buyers to search for UV light systems by configuration, application, specifications, and features.

UV System Configurations

UV light systems are available in a variety of configurations.

• Curing chambers are used for the curing or hardening of "dry" inks, coatings, and adhesives. They consist of a power supply, light source, and enclosure or chamber that provides a work surface and shields the operator from radiation.
• UV conveyors or continuous systems consist of a belt conveying unit, power supply and UV light source, as well as an enclosure that is open on both ends, which allows products or sheets to pass through the system. Conveyor systems allow for consistent, fast and safe UV curing. They prevent the cured item from being exposed to dust and contaminates in the air during drying.
• Hand held or portable UV devices are useful for repair and testing in field, laboratory, plant floor, and other settings where transportation of large systems is impractical.
• Flood or focused UV sources or modules are also integrated in production lines. Process or line-mounted UV systems include a power supply, light source and flange, cartridge mounting or fitting, web system, coating line, and conveyor lines or tanks that transport chemicals, plastic film, or other transparent media for processing.
• Spot or wand systems are benchtop units that provide a UV beam with a small spot size for selective curing applications.
• Wallorceiling-mounted UV systems disinfect anair stream as UV light irradiates theair circulating through the room. HVAC or duct-mounted systems are also available.

Configuration	Application
Curing chambers	Inks, coatings, and adhesives with dramatically improved physical properties, reduces of work-in-progress by completing the whole process in one machine, environmentally friendly - energy savings, no emissions controls
UV conveyors	Increases efficiency of curing process by increasing parts per cycle and drying time. Protects products from dust and contaminants during drying.
Hand held or portable	Counterfeit detection, surgery suites sterilization, room disinfector, forensics, water purifier, material processing and identification, dentist procedures.	.
Flood or focused	Fast curing of UV adhesives, coatings, and inks, industrial applications including UV bonding, sealing, and encapsulating, automotive, electronic, optical, and medical device assembly industries.
Spot or wand	Home disinfection, selective curing applications, forensic location and identification of materials
Mounted	Air and water purifier, product sterilization, insect control, can be integrated into conveying curing system,

UV Light System Applications

UV light has many applications in industry. Examples include the following.

• Curing of inks, adhesives, varnishes, coatings and electronic potting resins: Certain inks, coatings and adhesives are formulated with photoinitiators and resins, which polymerize when exposed to the correct energy and irradiance. This causes them to harden or cure. The reaction is very fast and is used in glass and plastic bonding, optical fiber coatings, dental fillings and finger nail gels. UV curing has been shown to increase production speed, reduce reject rates, improve scratch and solvent resistance, and facilitate superior bonding.

Video credit: Phoseon Technology / CC BY-SS 4.0

UV Ink Curing. Image Credit: Jeff Burton

• Security: Sensitive documents such as credit cards, driver's licenses and passports may include a UV watermark. Currencies for many countries also include an image and multicolored fibers that are visible under ultraviolet light.
• Forensics: Locating and identifying bodily fluids (e.g. semen, blood, fingerprints) can be done using UV light. Certain fibers, particles, and accelerants can be observed as well.
• Fluorescent lamps: By ionizing low-pressure mercury vapor, UV radiation can be produced so that a phosphorescent coating inside the tube of mercury absorbs the UV for conversion to visible light
• Astronomy: Astronomers use UV to identify sources of heat in space. Since the Earth's ozone blocks many UV rays, observations are generally made from space.
• Biology and Chemistry: Fluorescent dyes are used in biochemistry and forensics as genetic markers for research. Many plants and animals can use UV illumination to survive. Some plants benefit from using UV radiation as a light source for promoting growth. UV traps can also be used to eliminate small flying insects that are attracted to the light.
• Spectrophotometry: Chemical structure, fluorescence, and proteins can be analyzed using UV/VIS spectrophotometry.
• Air and water purification: UV light is an effective tool used to change irritating pathogens, pollens, and mold spores into inert byproducts by destroying their DNA and breaking down the organic material found in indoor air. A similar mechanism is used to kill germs and viruses in water.
• Analyzing and Authentication: Minerals, gems, art work, collectibles, and currency can be analyzed and authenticated using UV lamps due to their fluorescent properties. Papyruses and manuscripts can be read using UV light to distinguish ink from paper on the surface. UV lamps are used to identify and test materials, such as plastic and rubber.
• Medicine: UV lamps have a wide range of applications in medicine. Phototherapy is a treatment available for skin conditions like psoriasis and eczema, as well as vitamin D deficiency and certain fungal growths. Photochemotherapy is also a treatment available for psoriasis.
• Photolithography: Fine resolution for photoligthography can be achieved with UV radiation. The light causes chemical reactions to occur in the photoresist material to create a pattern on a sample. This technique is used in electronics and biomedical engineering.
• Sanitary compliance and sterilization: The DNA of microorganisms can be altered when exposed to UV radiation. When used in conjunction with other sterilization techniques, UV light is an effective tool to sterilize laboratory workbenches and medical facilities. UV lamps are also used to detect organic mineral and biological deposits that remain on surfaces, such as restrooms and bedding.
• Solar Cell Testing: Research is underway on converting UV radiation from the sun into energy and can be used as substitute for conventional window glass.

Application by wavelength:

Product Specifications

Selecting UV light systems requires an analysis of

• Intensity of the light. Intensity is defined by the light energy reaching a surface per time. It is often measured in mW/cm². The higher the intensity of the light, the faster the cure.
• Shortwave or longwave bulbs. Shortwave bulbs emphasize UVB and UVC while longwave bulbs are used from UVA and visible light. Longwave bulbs have a superior depth and substantial visible-light intensity.
• Distance and substrates affect intensity. Intensity decreases as the object's distance from the light increases and when curing through substrates that transmit less than 100% of the light used for curing.
• Lamp output power is the total lamp power that the UV system produces. Power should be considered when using portable or handheld devices.

Product Features

There are several specifications to consider when considering UV light systems. These include the following.

• Computer interfacing allows for programming, device control, and data acquisition.
• Filters can be integrated or optional and are used in analyzing and authentication applications.
• Meters or timers control exposure time.
• Multiple wand adaptation allows for multiple wands to be fed into the system.
• Multi-direction exposure UV systems can expose a product or material to light from multiple directions. This is important if the bond-to material is not transparent and shadows the adhesive from an overhead beam.
• Pulsed UV light systems and products that use light emitting diodes (LEDs) as a light source.

References

Electromagnetic Spectrum

Ionizing Radiation

Nature of UV

The Fluorescent Minerals

UV Information