Glossary of Terms

The law forecasts that every 10 years the amount of light generated by an LED increases by a factor of 20, while the cost per lumen (unit of useful light emitted) falls by a factor of 10.

The number of transistors in an integrated circuit doubles every two years.

The law describes the bending (refraction) of light rays crossing the boundary between dissimilar materials.

The loss of light as it passes through a material, generally due to its conversion to other energy forms (typically heat).

The decrease in optical power in amount of radiant energy per unit time, during passage through a fiber optic cable. Attenuation is due to such processes as absorption and scattering, and is typically measured in decibels per kilometer (dB/km)

(in relation to fiber-optic cable), the measure of information carrying capacity of a fiber-optic cable.

A beam of light is a bundle of light rays that may be parallel, converging or diverging. This directional nature of propagation is known as the intensity distribution of the bundle of light. When we talk of the irradiance distribution of the light source we are generally referring to the irradiance distribution on a plane perpendicular to the optical axis. It is easy to see that the irradiance distribution will change as a function of where this plane occurs along the optical and that this change depends critically upon the intensity distribution of the light. At positions close to and far from our light source there appears a hole in the irradiance distribution. At the position of our light guide the hole disappears and we obtain a bell shaped distribution.

A 3mm light guide accepts light only from the area of highest power density. This explains why a 3mm light guide has a higher irradiance than a 5mm light guide. However, a 5mm light guide accepts more light than a 3mm light guide, therefore a 5mm light guide has a higher power output than a 3mm light guide.

(in relation to fiber optic cable), the radius corresponding to the value that a fiber optic cable can bend prior to breakage or increase in attenuation.

A chemical substance that initiates or alters the rate of chemical reaction. (the catalyst itself is not affected by the reaction and is typically incorporated as a component in a two part adhesive).

To calculate the power of light impinging on an area, determine the area of exposure and multiply by the irradiance.

e.g. 10 W/cm2 at the end of a 5mm light guide

= 10W/cm2 * pi(0.25cm) sq = 10W/cm2 * 0.20cm2 = 2W

To calculate the irradiance from a power measurement, determine the area of exposure and divide the power by the area.

e.g. 2W at the end of a 5mm light guide

= 2W/ pi(0.25cm) sq = 2W/ 0.20cm2 = 10 W/cm2

The following chart provides a quick reference for converting between power and irradiance when measurements are made at the end of a standard light guide.

Converting from Irradiance to Power
	Light Guide
	2mm	3mm	5mm	8mm
Divide irradiance value by	32	14	5	2

Converting from Power to Irradiance
	Light Guide
	2mm	3mm	5mm	8mm
Multiply Power value by	32	14	5	2

A process of conversion of an adhesive from liquid to a solid state, accompanied by a physical modification of the adhesive. Converting a liquid to a solid can be accomplished by light curing or polymerization

A residual internal stress originating between different compounds during the curing process.

The gradual decrease over time in output signal with constant input light level

The total range of wavelengths, extending from the shortest to the longest wavelength or conversely, that can be generated physically. This range of electromagnetic wavelengths extends practically from zero to infinity and includes the visible portion of the spectrum known as light.

An adaptable group of thermosetting polymers for various applications (adhesion, sealing, encapsulation and coating), which can either be two part (room temperature curing), or one part (heat curing) and have great physical strength and excellent resistance to environmental damage and superior dimensional stability with excellent service temperature range.

A measure of the total amount of light transmitted, generated or received. The unit of energy is Joules (J). Energy is needed to activate a chemical reaction such as polymerization. UV and visible light are examples of radiant energy.

The total amount of energy delivered to an area. Dosage is the product of irradiance and time. Units: = J/cm²

OmniCure® systems can provide 20,000mW/cm² of irradiance
20,000mW/cm² x 10sec = (20J/sec/cm²) x 10sec = 200 J/cm²

(in relation to photonics) a dielectric material that guides light (i.e. a wave guide).

A cable made up of one or a number of optical fibers.

The branch of photonics related to the transmission of light through optical fibers for the purpose of data or image transmission.

A measure of the extent of a function. Given by the difference between the two extreme values of the independent variable (e.g. lateral displacement) at which the dependent variable (e.g. irradiance) is equal to half of its maximum value. Commonly applied to the spectral extent of emission or absorption lines, and the angular or spatial extent of radiation patterns.

A substance that is added to an adhesive composition in order to control/promote the curing reaction by taking part in it.

A substance that is added to an adhesive composition in order to slow down the rate of chemical reaction.

Flux per unit solid angle. Units are watts/steradian. It is common for the term intensity to be mistakenly used in place of irradiance.

The law stating that the illuminance (or irradiance) from a point source varies as the inverse square of the distance between the source and the receiver.

The decrease in irradiance for a spot curing system deviates somewhat from the inverse square law, due to the assumption of a point source vs. the typical 5mm diameter light guide. The importance remains that the distance between the light guide and the adhesive must be strictly controlled to insure that that the correct dosage of light is delivered. Most irradiance measurements are taken at the end of the light guide, although ideally they would be taken directly at the cure site.

Also referred to as power density, irradiance is the amount of power delivered into a specified area, i.e. energy/time/area Units: J/sec/cm² = Watts/centimeter2 (W/cm²)

The usable life of a mercury arc lamp depends on several factors including number of starts, operating time per start, temperature and irradiance level. Electrode wear is a major cause of the light level degradation that determines lamp replacement time. The brightness and radiance are at a maximum at the cathode tip, and decrease toward the anode. As the lamp operates the cathode tip slowly erodes, causing the high brightness point to move along with it. The gradual deposition of opaque evaporated tungsten (electrode material) on the inner wall of the bulb decreases the radiance of the lamp. Frequent ignition accelerates electrode wear and hastens this process.

(in relation to photonics). The region of the electromagnetic spectrum in the range between the near-ultraviolet region and the infrared region.

A semiconductor device (diode) that emits light spontaneously from the p-n junction under applied forward current.

A filament of transparent dielectric material (glass or plastic) that is typically circular in cross section and that guides light. An optical fiber consists of a cylindrical core surrounded by a cladding of similar geometry and lower refractive index, so that light can be guided by the fiber.

The technology field related to the generation, transmission and control of light for communications and information processing. It includes the emission, deflection, amplification, transmission and detection of light by employing various optical components and devices such as fiber optics, light sources and optoelectronic instrumentation.

Energy is needed to activate a chemical reaction. UV and visible light are examples of radiant energy. UV and Visible light can be seen on the electromagnetic spectrum.

The free radicals / catalysts and resins react to create polymer chains, transforming the adhesive from a liquid to a "solid". (Elastic to completely rigid, depending on application and UV dose.)

Energy delivered in a specified amount of time. The units for power are Joules/sec or Watts (W). The OmiCure® S1000 and S2000 UV Curing systems use 100-Watt and 200-Watt Hg arc lamps respectively.

The science of radiation measurement concerned with the detection and measurement of radiant energy, either at separate wavelengths or integrated over broad wavelength bands; and the interaction of radiation with matter in such ways as absorption, reflectance and emission.

The irradiance per unit wavelength interval at a given wavelength, expressed in watts per unit area per unit wavelength interval. For spot curing, it is very important that the spectral irradiance of the lamp matches the spectral absorption of the photoinitiators in the adhesive.

The reflection that occurs within a substance because the angle of incidence of light striking the boundary surface is in excess of the critical angle.

The conduction of radiant energy through a medium. Transmission is often specified by the percentage of energy passing through an element or system relative to the amount that entered. Note: light guide throughput values are based upon the transmission properties of the guide. The actual output from the light guide vs. the source will vary depending upon the amount of light entering the guide from the source. e.g. although a standard bifurcated light guide will transmit 80% of the light entering the guide, part of the source light falls on the space between the inputs and does not enter the guide, resulting in a lower output.

The region of the electromagnetic spectrum in the range between 10 - 400nm.

An adhesive in which the chemical curing process is initiated by ultraviolet (UV) light.