uv curig terminology.png

General UV output and measurement terms applicable to all sources.

 

UV LED

Terms and definitions specific to UV LED sources.

 

Arc & Microwave

Terms and definitions specific to electrode (arc) and microwave sources.

 

UV measurement terms published by RadTech.

 

General UV
RadTech
General UV Terminology

absorption – not reflecting. The partial loss in energy from light passing through or not reflecting off a medium.

 

actinic UV – low powered UVA.

 

adhesion – state in which two surfaces are stuck together. The degree of force required to separate or destruct the bonds varies by substrate, formulation, and cure. See destruct bond.

 

ASTM spec D3359-95a – see tape test.

 

black light – low powered UV composed of longer UVA and near visible wavelengths.

 

cationic chemistry – UV chemistry that requires minimal direct line-of-sight UV exposure to begin the cure process. The majority of the cure takes place as a chemical reaction that occurs within a few hours or a few days after the UV exposure.

 

cross hatch test – see tape test.

 

crosslinking – process of forming covalent bonds or relatively short sequences of chemical bonds to join two polymer chains together. When polymer chains are crosslinked, the material becomes more rigid.

 

cure – a drying process that occurs through a chemical reaction between a UV formulated ink, coating, or adhesive and UV light.

 

dose (dosage) – see energy density. Dose is slightly different than energy density in that dose is the total absorbed energy and not the total delivered energy.

 

dynamic exposure – exposure to a varying irradiance. It occurs when a lamp head passes over a substrate without pausing or when a substrate passes under a lamp head without pausing.

 

dynamic range – span between the minimum irradiance and the maximum irradiance to which a radiometer will accurately respond. Measured in Joules/cm2.

 

electromagnetic spectrum – full wavelength range of electromagnetic radiation including microwave, ultraviolet, visible, and infrared energy.

 

energy density – total radiant energy delivered to a particular area (measured in J/cm2 or mJ/cm2). Energy density is the integration of irradiance (W/cm2 or mW/cm2) over exposure time (line speed or dwell). Though technically incorrect, it is also referred to as dose.

 

erythemal UV – low powered UVB.

 

flux – flow of photons and measured in einsteins / second.

 

free radical chemistry – UV chemistry that requires direct line-of-sight UV exposure in order for the formulation to cure.

 

frequency – number of times a periodic wavelength cycle occurs in one second. Unit measure of Hertz (Hz) or cycles per second.

 

germicidal UV – UV in the UVC band.

 

infrared energy – energy having wavelengths between 1 and 100 µm. Provides a radiated heat component in electrode and microwave UV systems.

 

intensity – see irradiance.

 

interlock – internal or external device to the UV source unit. An internal interlock is often a temperature (LED) or pressure sensor (conventional UV) and / or flow meter (liquid-cooled systems) designed into the cooling system to monitor proper conditions and switch off the UV system when conditions are not met. An external interlock is typically implemented by the integrator or machine builder. It is a safety feature to prevent the light source from turning on or to make it shut off under certain conditions, such as when a machine door is open or if the web or parts stop moving.

 

irradiance – radiant power arriving at the surface from all forward angles. It is usually expressed in watts and milliwatts per square centimeter (W/cm2 or mW/cm2). It is independent of line speed and exposure time. It decreases at the cure surface as the distance between the cure surface and the lamp increases. Though technically incorrect, it is also referred to as intensity.

 

joule – metric unit for measuring work or energy. One joule is equivalent to the work done by a force of one Netwon (N) acting through a distance of one meter. It is the time-integral of power. One joule equals one watt per second. Abbreviated J (or mJ for millijoule).

 

micrometer – metric unit of length equal to one millionth of a meter. Abbreviated µm.

 

monochromatic – UV output confined to a very narrow bandwidth. UV LED sources are relatively monochromatic. See polychromatic.

 

monomer – molecule of relatively low molecular weight and simple structure capable of combining with itself or other similar molecules to form polymers.

 

nanometer – metric unit of length equal to one billionth of a meter (abbreviated nm). It is the most common unit used to describe the wavelength of light, with visible light falling in the region of 400 to 700 nm. Ultraviolet light falls within the range of 200 to 400 nm.

 

nitrogen blanketing – see nitrogen inerting.

 

nitrogen inerting – when the surface of the applied formulation is flooded with a nitrogen blanket to prevent the coating or ink from oxidizing before cure. Nitrogen inertion reduces oxygen inhibition.

 

oligomers – low molecular weight resin or polymer used in a radiation curable formulation.

 

oxidizing – when the formulation reacts with oxygen and slows the polymerization of the cure. The higher the ratio of exposed surface area to formulation mass, the more negative the impact oxygen has on the cure.

 

oxygen inhibition – retardation of UV polymerization by the interaction of oxygen with photoinitiators and free radicals. Reduces surface cure of the polymer.

 

parts per million (PPM) – units of the Threshold Limit Value (TLV) when referring to the maximum level of a substance that a person should be exposed to over an 8-hour shift during a 40-hour week without producing an ill effect. See Threshold Limit Value (TLV).

 

peak irradiance / peak power density – maximum irradiance or dose rate measured over a sample period. Unit measure of (Joules/cm2 · sec) or Watts/cm2. See irradiance.

 

photoinitiator – molecule which when exposed to a specific wavelength of energy starts a reaction that begins the cure process.

 

photopolymerization – chemical process where a UV formulated ink, coating, or adhesive is converted to a cross-linked polymer through exposure to UV energy.

 

polychromatic – UV output consisting of a wide bandwidth. See monochromatic.

 

polymer – a macromolecule consisting of a large number of monomer units.

 

post cure – chemical or physical reactions in the formulation that occur after UV exposure has ceased.

 

power density – see irradiance. 

 

radiant power – rate of energy transfer expressed in Watts or Joules/sec.

 

radiometer – device used to measure incident irradiation on a sensor element. Its construction may incorporate either a thermal detector or a photonic detector. The instantaneous signal output will usually have a linear proportionality to radiant flux and will depend on incident wavelengths. The resulting characteristic response to irradiance versus wavelength is called responsivity.

 

spectral output – (1) various wavelengths of light emitted from a UV source.  (2) the radiant output of a lamp or LED array versus wavelength. Spectral output can be displayed in a variety of ways, but it is commonly shown as a graph or chart illustrating UV irradiance in Watts or Watts/cm2 plotted against wavelength. The irradiance can be shown in absolute terms or normalized.

           

spectral output efficiency graph – graph or chart showing the relative concentration of UV at various wavelengths for a particular bulb (lamp) type. Typically, the concentration is provided as a normalized percentage where the energy is integrated over 10-nanometer bands to reduce the difficulty of quantifying the effects of line emission spectra. 

 

static exposure – exposure to a constant irradiance over a controlled time period.

 

surface cure – reference to the cure on the outermost material surface exposed to the UV rays.

 

tape test for measuring adhesion – an X-cut or lattice pattern of 6 or 11 cuts are scratched through the UV cured material to the substrate. Special pressure-sensitive tape is then applied over the cuts and then pulled away. Pulling the tape away from the substrate will reveal the degree of adhesion of the cured formulation to the substrate or media. If any material between the lines is pulled off with the tape, the adhesion is poor. If the cured material remains, the adhesion is good. The recommended guidelines for testing and evaluation are documented in the ASTM spec D3359-95a under Methods A and B. Method A employs the X-cut and is used for films that are greater than 5 mils. Method B calls for lattice cuts and is recommended for films with 0-5 mils thickness.

 

Threshold Limit Value (TLV) – maximum exposure a person should be exposed to over an 8-hour shift during a 40-hour week without producing an ill effect. Often reported in mg / m3 or parts per million (ppm).  See parts per million.

 

through cure – when the formulation is cured down to and including the material / substrate interface layer. Good through cure does not necessarily mean good adhesion.

 

Time Weighted Average (TWA) – see threshold limit value (TLV).

 

total energy – see energy density.

 

total power – rate of energy transfer expressed in Watts or Joules/sec. For LEDs, total power is measured in an integrating sphere.

 

transmittance – ratio of the radiant energy passed through a body to the total radiant energy received by the body.

 

ultraviolet light (UV light) – electromagnetic radiation with wavelengths shorter than visible light and longer than X-rays. UV spans the range of 200 to 400 nm. The name is due to the wavelengths being just outside those identified by the human eye as having the color violet.

 

UVA (315 – 400 nm) – portion of the electromagnetic spectrum ranging between 315 and 400 nm. UVA represents the largest portion of UV energy and is commonly referred to as long UV. UVA is most responsible for skin aging and increased skin pigmentation. UVA is the lower limit of sensitivity to the human eye.

 

UVB (280 – 315 nm) – portion of the electromagnetic spectrum ranging between 280 and 315 nm. UVB is most responsible for reddening and burning of the skin and damage to the eyes. Invisible to the human eye.

 

UVC (200 – 280 nm) – portion of the electromagnetic spectrum ranging between 200 and 280 nm. UVC is commonly referred to as short UV. Invisible to the human eye.

 

UVV (400 – 445 nm) – portion of the electromagnetic spectrum ranging between 400 and 445 nm. The V stands for visible.

 

vacuum UV – portion of the electromagnetic spectrum ranging between 100 and 200 nm. UVV does not transmit in air.

 

viscosity – measure of a fluid’s resistance to flow. Measured in centipoise (cp or cps). Water is 1 cp. Blood is 10 cp. Honey is 2,000 cp.

 

watt – unit of power, one joule per second.

 

watt density – see irradiance.

 

wavelength – distance between corresponding points of a propagated wave. UV wavelengths are typically measured in nanometers (nm). Designations of UV wavelengths are wide ranging and were originally established to define limits for distinction of physiological effects due to UV exposure. Generally accepted ranges include:  V-UV 100-200 nm, UV-C 200-280 nm, UV-B 280-315 nm, UV-A 315-400 nm, and UV-V 400-450 nm.

 
UV LED Terminology

anode – positive terminal of an LED.

 

binning – process of sorting discrete LEDs according to peak irradiance, wavelength tolerance, and forward voltage.

 

borosilicate – strong, heat-resistant, colorless, silica glass that contains a minimum of five percent boric oxide, exhibits exceptional thermal shock resistance, and transmits a greater percentage of ultraviolet energy than glass. Common material used for emitting windows, plates, reflectors, lenses, and other optics.

 

cathode – negative terminal of an LED.

 

chip – fully functioning slice of a semiconducting material, such as silicon, germanium, and gallium arsenide doped and processed to have p-n junction characteristics.  Specifically, gallium nitride (GaN) is used to generate longer ultraviolet UVA and blue visible wavelengths. In referring to LEDs, chip is often used interchangeably with diode, die, and semiconductor.

 

coolant – liquid circulation material that flows over or through the heat sink in a liquid-cooled LED head in order to (1) remove excess heat energy generated by inefficiencies in the electroluminescence process and (2) maintain the desired operating temperature of the LEDs and wire bonds. 

 

DC power supply – device that supplies electric energy of fixed polarity, either positive or negative, to power LEDs. DC means direct current. Direct current is an alternative to AC or alternating current.

 

depletion zone – non-conductive boundary where the positive and negative sides of a p-n junction meet.

 

die – fully functioning slice of a semiconducting material, such as silicon, germanium, and gallium arsenide doped and processed to have p-n junction characteristics. Gallium nitride (GaN) is used to generate longer ultraviolet and blue visible wavelengths. In referring to LEDs, die is often used interchangeably with chip, diode, and semiconductor.

 

diode – a semiconductor that is added to a circuit as a means of restricting the flow of electricity. It can be thought of as a switch or a valve. A key property of a diode is that it only conducts electricity in one direction. In referring to LEDs, diode is often used interchangeably with chip, die, and semiconductor.

 

doped LED – refers to an LED semiconductor material that has been impregnated with impurities during the manufacturing process to produce a specific n-type or p-type conductivity and influence the wavelength output.

 

driver / driver board – printed circuit board (PCB) that distributes the DC voltage to the LEDs or modules in an assembly and often provides additional control features.

           

dual cure – UV LED chemistry formulated to also cure with conventional microwave or electrode arc lamps.

 

duty cycle – proportion of ON time in a pulse width modulation (PWM) cycle to the total cycle time (ON + OFF) expressed as a percentage.  A low duty cycle corresponds to a low power because the LEDs are OFF most of the time. 100% is fully ON, and 0% is fully OFF. 50% means that the power is ON half the time and OFF half the time. Varying the duty cycle but not the input power changes the energy density while maintaining a constant irradiance. Not all LED systems incorporate a PWM duty cycle.

 

electroluminescence – optical and electrical phenomenon inherent to LEDs in which a material emits light energy when an electric current is passed through it. 

 

emitting window – flat and typically rectangular or square piece of quartz or borosilicate secured and often sealed at the base of an LED head to physically protect the LEDs while simultaneously transmitting ultraviolet wavelengths. See quartz plate.

 

encapsulate – transparent material sometimes applied to dies for protection and to seal the dies from dirt and moisture.

 

forward bias – a state that occurs when the anode of an LED is connected to the positive terminal of a voltage supply and the cathode of the LED is connected to the negative terminal. The effect of a forward bias is that the positive holes in the p region and the negative electrons in the n region of a p-n junction are pushed from opposite directions toward the depletion zone. This significantly reduces the effect of the depletion zone causing the electrons on the n-side to respond to the attractive forces of the holes on the p-side. The result is recombination, the flow of electricity, and the emission of photons.

 

forward voltage – voltage across a semiconductor diode carrying a forward current.

 

integral blower / fan – refers to the system cooling fan when it is mounted directly on the lamp head.

 

integrating sphere – an optical component consisting of a hollow spherical cavity with its interior surface covered with a diffuse white reflective coating. Also known as an Ulbricht sphere. There are small holes or openings in the sphere for inserting emitting sources. The sphere allows for a uniform scattering or diffusing of emitted light from the source such that the source’s output can be measured in Watts free of any special direction. This is an R&D device and not something used on press or in the field. 

 

Lambert’s cosine law – radiant intensity or luminous intensity observed from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to the cosine of the angle θ between the direction of the incident light and the surface normal.

 

lambertian – when an emitting surface has the same radiance when viewed from any angle. In other words, it has the same apparent brightness (or luminance).

 

lambertian source – optical source that obeys Lambert's cosine law. LEDs approximate a Lambertian source in that they have a large beam divergence and a radiation pattern that approximates a sphere.

 

LED (light emitting diode) – semiconductor, p-n junction device designed to emit specific narrow band wavelengths within the electromagnetic spectrum via a process known as electroluminescence. When a forward bias voltage is applied to the LED, current flows from the p-side to the n-side (anode to cathode). As the electrons cross the depletion zone and fill a hole, they drop into a state of lower energy. The excess energy is released in the form of a photon. The energy of the photon is directly related to the amount of excess energy while the wavelength of the photon is inversely related to the excess energy. In other words, the higher the excess energy the shorter the wavelength. Common UV LED wavelengths are 280, 365, 385, 395, and 405 nm.

 

LED array – (1) packaged sub-assembly or module typically consisting of multiple diodes or chips that are individually wire bonded to a printed circuit board (PCB) and secured to a heat sink. LEDs can be arranged in a single line, a matrix, or other pattern. (2) full curing assembly which includes numerous modules or LEDs as well as an internal cooling fan(s) or liquid manifold with tube fittings for connecting to a chiller. Also includes a heat sink, an emitting window, and an outer enclosure. In some cases, a complete array assembly will also contain the driver boards. The array is similar in concept to a lamp head or irradiator in traditional UV curing systems.

 

LED irradiator, head, lamp, lamp head, light source, LED dryer, or light engine – full curing assembly which includes numerous modules or LEDs, a thermal heat management system, an internal cooling fan(s) or liquid manifold with tube fittings for connecting to a chiller. Also includes a heat sink, an emitting window, and an outer enclosure. In some cases, a complete array assembly will also contain the driver boards.

 

LED package – assembly containing one or several diodes and a means of electrically connecting the entire assembly to another device.

 

lens – transparent optical device used to redirect or columnate light output. In LED systems, a lens also acts to physically protect LED chips, reduce exposure to dust and moisture, and evenly spread the emitted UV radiation. A lens can be attached to each individual LED, a group of LEDs, or span the length of a line of LEDs.  Often made of borosilicate or quartz. See encapsulate.

 

liquid chiller or cooler – cooling system that circulates coolant through the light source). It is used to (1) ensure the LED chips and wire bonds remain at the correct operating temperature and (2) to remove excess heat energy created by inefficiencies in the electroluminescence process. Some systems require refrigerated coolant while others use coolant cooled by ambient air blast units.

 

module – packaged sub-assembly typically consisting of multiple diodes or chips that are individually wire bonded to a printed circuit board (PCB) and secured to a heat sink. LEDs can be arranged in a single line, a matrix, or other pattern. Designs vary, but a module can also include an encapsulate, lens, or emitting window over the chips for protection and to reduce exposure to dust and moisture. A module is an array, but several modules can also be assembled together to form a larger array known as a head or irradiator.

 

negative cooling – when cooling air for a lamp head is drawn from the area surrounding the substrate or part being cured through the lamp head.

 

optical device – device used to redirect, focus, or columnate light output emitted from an LED or array of LEDs.

 

pinning – process used in UV digital inkjet printing where ink is partially cured after being jetted to reduce dot gain and provide a sharper more vibrant image or to cure the under white before additional colors are jetted on top of the white. A secondary, full cure source is required following pinning.

 

plug-in-module – packaged assembly consisting of one or multiple LED diodes that are individually wire bonded to a printed circuit (PCB) which is then secured to a heat sink. A module often includes a an encapsulate or lens over the chips for protection and to block air and moisture. A module is an array, but several modules can also be assembled together to form a larger array known as a head or irradiator.

 

positive cooling – when cooling air for a lamp head is blown into and through the lamp head. Positive cooling can be supplied through either an external blower ducted to the assembly or through an integral blower or fan mounted within or on the assembly.

power supply unit (PSU) – can refer to an off-the-shelf DC power supply component or the entire electrical cabinet containing the DC power supply component(s), I/O interface, AC power connection, and other items. Driver boards can be mounted in the cabinet or on the array. Sometimes referred to as the Controller if it contains the operator interface.

 

printed circuit board (PCB) – part of the LED module or array to which the individual LED chips or diodes are wire bonded or connected. The PCB provides the electrical interface between the LED chip(s) and the driver board(s).

 

positive-negative junction (p-n junction) – specially engineered diode made by growing layers of semiconductive materials. Impurities or dopants are impregnated or doped into the semiconductor layers to create p and n-type regions. These regions can be made from the same or different semiconductor materials. The two sides of the diode are referred to as the anode (+) and the cathode (-) respectively. Current flows from the p-side of the diode to the n-side when connected to a DC power source.

 

pulse width modulation (PWM) – modulating or varying the width of a pulse. This is a digital signal that employs a duty cycle to vary the ON time that power is delivered to an electronic component. Varying the duty cycle but not the input power changes the energy density while maintaining a constant irradiance. Not all LED systems incorporate a PWM duty cycle.

quartz filter – see quartz tube (3).

 

quartz plate – plates made from quartz or borosilicate that allow UV energy to penetrate with minimal loss in irradiance and are mounted in front of the lamp head. Another term for emitting window.

 

quartz tube – an open tube made from a silicate material. The tube is placed in front of a UV lamp head or inside the assembly and flooded internally with nitrogen. Parts traveling through the tube, such as fiber optics, are safeguarded from exposure to air and ozone in order to improve cure.

 

remote blower – refers to the system cooling fan when it is mounted separate from the lamp head and ducted into the lamp head assembly.

 

semiconductor – substance that can be made to conduct electricity or be an electrical insulator depending on its chemical composition. The conductivity and output wavelength of the semiconductor varies depending on its material construction, impurities (dopants), and concentration of dopants. Common semiconductor base materials include silicon, gallium nitride, gallium arsenide, and gallium phosphide.

 

solid-state electronics – circuits or devices built entirely from solid materials and no moving parts.

 

total power – rate of energy transfer expressed in Watts or Joules/sec. For LEDs, total power is measured in an integrating sphere.

 

wire bond – electrical connection or solder joint between the LED chip and the printed circuit board (PCB). There are two wire bonds between each LED and the PCB. These wire bonds occur at the anode and the cathode.

 
Arc and Microwave Terminology
 

additive bulb (lamp) – mercury bulb (lamp) containing metal additives such as iron, gallium, indium, tin, or others. These bulbs (lamps) produce variations in spectral output with a mercury only bulb (lamp) as the reference.

 

arc length – distance measured between the electrodes in a quartz bulb (lamp). See effective cure length.

 

ballast – an inductive transformer device that stabilizes the amount of current flowing through the bulb (lamp) so that the power output remains constant.

 

borosilicate – strong, heat-resistant, colorless, silica glass that contains a minimum of five percent boric oxide, exhibits exceptional thermal shock resistance, and transmits a greater percentage of ultraviolet energy than glass. Common material used for plates, reflectors, lenses, and other optics.

 

bulb (lamp) – sealed quartz tube containing a mixture of inert gas and mercury under medium pressure. Electrode bulbs (lamps) are fitted with electrical connections at the ends of the bulb (lamp). Microwave bulbs (lamps) contain no electrical connections. The mercury and inert gas are energized (vaporized) by either a voltage arc or microwave energy. The vaporized plasma emits UV light.

 

burn-in-period – second stage of the start-up process of a UV bulb (lamp) and is the total time it takes the current and voltage inside the bulb to stabilize during start-up.

 

capacitor – corrects the power factor in the main power supply to reduce current levels in the UV system.

 

cold mirror – reflector that is coated with a dichroic material that absorbs or passes wavelengths in the infrared range while reflecting those in the UV range. See dichroic.

 

cassette (cartridge, cradle) – supports the UV bulb (lamp) and reflector inside the lamp housing. Typically a removeable assembly allowing for easier maintenance.

 

cure length – see effective cure length.

 

dichroic – a coating designed to pass or absorb certain wavelengths and reflect other wavelengths. In UV lamp heads, dichroics are used on reflectors to pass infrared energy and reflect UV energy.

 

devitrification – act of making quartz glass opaque through prolonged heating and UV exposure.

 

doped bulb – see additive bulb.

 

effective cure length – length of a bulb (lamp) that delivers optimal UV output. For electrode bulbs (lamps), the effective cure length is always less than the arc length. For microwave bulbs (lamps), the effective cure length is the length of the bulb (lamp).

 

electrode – electrical fitting at the ends of an arc lamp (bulb). The electrode consists of a tungsten pin surrounded by a tungsten coil and is used to maintain a voltage arc across the bulb (lamp). Electrode is also used to refer to the style of bulb or system when differentiating between microwave and electrode bulbs and microwave and electrode systems.

 

electrodeless – a microwave powered UV system. Refers to the fact that microwave bulbs (lamps) do not have electrodes.

 

flood – an unfocused band of UV light that is more evenly distributed across the width of a reflector. To generate the flood, lamp heads use a parabolic reflector instead of an elliptical reflector.

 

focal distance (length) – perpendicular distance from the edge of the lamp head to the point where the UV light emitting from the bulb (lamp) converges. This is the location of maximum UV concentration. Only applies to arc and microwave systems. Not LEDs.

 

focus – line external to the lamp head where the UV energy reflected from the lamp head is at its highest concentration. Only applies to arc and microwave systems. Not LEDs.

 

gallium – a bluish white metallic element used in additive mercury bulbs (lamps). The gallium additive provides a yellowish tint to an unenergized UV bulb and a violet coloration to the UV output. Gallium bulbs have a spectral peak around 417 nm and a spectral concentration between 400 and 450 nm. They are often used when deeper cure is required or with white formulations containing titanium oxides. In some industries, microwave gallium bulbs are referred to as V bulbs.

 

igniter – see starter.

 

indium – silver white metallic element used in additive mercury bulbs (lamps). The indium additive provides a yellowish tint to an unenergized UV bulb and a violet coloration to the UV output. Indium is used to shift the spectral output past 400 nm. In some industries, microwave indium bulbs are referred to as Q bulbs.

 

integral blower – refers to the system cooling fan when it is mounted directly on the lamp head.

 

integral shutter – a shutter assembly that is built into the lamp head. Common designs include a pneumatically actuated clam shell that blocks the light when closed and acts as a reflector when open and a pneumatic slide mechanism that moves the lamp head behind an internal louver when shuttered.

 

irradiator – see lamp head.

 

lamp – see bulb.

 

lamp head – assembly containing a housing, UV bulb, and integral or remote cooling fan. An electrode system often contains a removeable cassette subassembly while a microwave system contains magnetrons, a cavity, and an RF screen.

 

liquid chiller or cooler – cooling system used with some arc lamp systems. It circulates coolant through the lamp housing and quartz filter if used.

 

louver – part of a UV shutter system or shielding section that blocks UV light while allowing cooling air to pass through.

 

magnetron – assembly contained inside a microwave lamp head that converts high voltage electrical input into RF energy.

 

mercury – a silver-white metallic element that is liquid at room temperature and is used to create a vaporized, UV-emitting plasma gas inside a quartz tube when it is energized through the use of either a voltage arc or microwave energy. When energized the bulb produces a bright white UV output. Mercury bulbs have a peak spectral output around 365 nm and a concentration around 254 nm. In some industries, microwave mercury bulbs are often referred to as H bulbs.

 

mercury arc – electric discharge passed between two electrodes and through a mercury vapor medium inside a quartz tube.

 

mercury plus (H+) – refers to microwave bulbs (lamps) that contain additional mercury. Mercury plus bulbs are only available in microwave lamps.

 

metal halide – see additive bulb (lamp).

 

microwave – part of the electromagnetic spectrum between one millimeter and one meter. These wavelengths are longer than infrared waves and shorter than radio waves.

 

negative cooling – when cooling air for a lamp head is drawn from the area surrounding the substrate or part being cured through the lamp head. Negative cooling also provides exhaust for the UV system if it is ducted away from the press and/or out of the facility. Negative cooling is most often supplied with a remotely installed cooling fan (blower).

 

out of focus – when a lamp head is located further away from the substrate or closer to the substrate than the focal distance. An out of focus lamp delivers less irradiance to the cure surface than when the substrate is located at the focus.

 

ozone (O3) – unstable, colorless gas with a penetrating odor that is generated by the reaction of short-wavelength UV light typically in the range of 160 to 240 nm.

 

ozone inhibiting (ozone free bulbs) – bulbs (lamps) where the quartz is manufactured with an additive that prevents the transmission of shorter UV wavelengths.

 

planar shutter – shutter assembly that is externally attached to a lamp head. The louvered shutter moves perpendicular to the emitted UV light.

 

positive cooling – when cooling air for a lamp head is blown into and through the lamp head. Positive cooling can be supplied through either an external blower ducted to the assembly or through an integral blower or fan mounted within or on the assembly. With positive cooling, an additional exhaust system is required to remove heat and ozone.

 

quartz plate – plates made from quartz or borosilicate that allow UV energy to penetrate with minimal loss in irradiance and are mounted in front of the lamp head. The plates are used to prevent positive cooling air and air-borne contaminants from contacting the substrate or part, negative cooling air from contaminating the bulb and reflectors, or to remove some of the heat that is radiated from the UV bulb (lamp). If the goal is to reduce the amount of heat contacting the substrate, additional cooling air must be blown across the quartz. If additional cooling air is not used, the quartz will eventually heat-up and begin radiating heat onto the substrate. To further reduce heat, the quartz can be coated with a material that passes UV light and absorbs infrared energy.

 

quartz tube – (1) a sealed tube made from a silicate material that is filled with a precise mixture of mercury and various inert gases and sometimes fitted with electrical connections. The vaporized mercury emits light when it is energized through the use of either a voltage arc or microwave energy. Often used to refer to the bulb (lamp).  (2) an open tube made from a silicate material. The tube is placed in front of a UV lamp head or inside the assembly and flooded internally with nitrogen. Parts traveling through the tube, such as fiber optics, are safeguarded from exposure to air and ozone in order to improve cure.  (3) an open tube made from a silicate material. The tube is placed in front of a UV lamp head and flooded internally with distilled water. The water absorbs infrared energy from the bulb (lamp) and carries it away from the press environment. Also known as a quartz filter.

 

reflector – reflects and concentrates the UV light onto the substrate or part. Rolled from highly polished aluminum sheet metal or formed from borosilicate into elliptical or parabolic profiles. Elliptical profiles optimize the concentration of UV energy that is reflected off the bulb (lamp) by guiding the radiation into a tightly focused UV band. A parabolic reflector results in a flood of UV light. Holes or slots in the reflector allow cooling air to pass through the reflector to the bulb (lamp). The holes or slots are engineered for size and location to provide both optimal and balanced airflow across the length of the bulb.

 

remote blower – refers to the system cooling fan when it is mounted separate from the lamp head and ducted into the lamp head assembly.

 

RF – radio frequency. Any frequency between normally audible sound waves and the infrared light portion of the spectrum lying between 10 KHz and 1,000,000 MHz. Used to vaporize the mercury in microwave bulbs (lamps).

 

RF detector – monitors RF levels in the vicinity of the UV system and signals the power supply to switch off the UV if RF levels exceed allowable limits.

 

screen – a wire mesh assembly attached to a microwave lamp head that allows UV to pass through but prevents RF from leaking outside the unit.

 

shutter – an assembly designed to block UV light emitted from a lamp head while simultaneously allowing the flow of cooling air.

 

solarization – effect of UV light on a quartz bulb (lamp). Over time, UV light and heat will cause the quartz to devitrify or revert back to its crystalline and cloudy state.

 

solid-state electronics – circuits or devices built entirely from solid materials and no moving parts.

 

starter – used in electrode, ballast-based systems to vaporize the mercury at start-up. Applies a several thousand-volt potential across the bulb during start-up. An internal circuit discontinues the potential when current is established across the bulb (lamp).

 

starter bulb – used in the start-up of a microwave system to ignite the mercury vapor in the bulb.

 

static exposure – exposure to a constant irradiance over a controlled time period.

 

striking – initiating the start-up process when the mercury in the bulb (lamp) is first vaporized.

 

vitrification – act of changing pure opaque quartz into glass through fusion.

 

waveguide – directs microwaves toward the bulb (lamp) in microwave systems.