Dictionary of Light Technology Terms: N - Z

N

N-Type

Negative semiconductor material in which there are more electrons than holes; current is carried through it by the flow of electrons.

Nanotube

See Carbon Nanotube.

Nyquist Limit

The limiting resolution of a camera's sensor, generally defined as being one half the sampling frequency.

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O

Ohm

A measure of the electrical resistance of a material equal to the resistance of a circuit in which the potential difference of 1 volt produces a current of 1 ampere.

One-Axis Tracking

A photovoltaic array tracking system capable of rotating about one axis.

Optics

The branch of physical science that studies the behavior and properties of light, in the wavelength range extending from vacuum ultraviolet at about 40 nm to the far-infrared at 1 mm. Because light is an electromagnetic wave, other forms of electromagnetic radiation exhibit similar properties.

Organic Light Emitting Diode (OLED)

A semiconductor display device that sandwiches carbon-based films between two charged electrodes, usually of glass. Similar to LEDs, when electrons and holes combine in the organic layer (i.e. when voltage is applied to the OLED cell), they emit photons, creating electro-luminescent light.

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P

Parabolic Trough

A trough-type solar collector with cylindrical parabolic mirrors that focus the reflected light on a special tube mounted in front of it.

Peak Sun Hours

The equivalent number of hours per day when solar irradiance averages 1,000 w/m2. For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1,000 w/m2.

Peripheral Component Interface (PCI)

A PC local bus designed by Intel, which runs at 33 MHz and supports Plug and Play.

Phonon

A quantum of sound. It is the lowest energy, quantized state of a vibration within a lattice structure, such as those created by the atoms of matter. In analogy to a photon (a quantum of light), a phonon is viewed as a wave packet with particle-like properties.

Phosphorous

A chemical element used as a dopant in making n-type semiconductor layers.

Photocurrent

An electric current induced by radiant energy.

Photodetector

Photodetectors are semiconductor devices used for the detection of light by converting light energy (photons) into electrical energy.

Photodiode

A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.

Photoelectric Cell

A device for measuring light intensity that works by converting light falling on, or reaching it, to electricity, and then measuring the current. Used in photometers.

Photoelectrochemical Cell

A type of photovoltaic device in which the electricity induced in the cell is used immediately within the cell to produce a chemical, such as hydrogen, which can then be withdrawn for use.

Photometer

An instrument used to measure various aspects of the intensity of light.

Photomultiplier

A device, normally in the form of a vacuum tube, that uses a photocathode to convert photons into photoelectrons which are then amplified.

Photon

A particle of light that acts as an individual unit of energy.

Photoreflectance (PR)

A noncontact form of electromodulation in which modulation of the electric field is caused by photo-excited electron-hole pairs from a pump source.

Photovoltaic

Pertaining to the direct conversion of light into electricity.

Photovoltaic Cell

The smallest semiconductor element within a PV module, consisting of layers of semiconductor materials fabricated to form a junction (adjacent layers of materials with different electronic characteristics) and electrical contacts, to convert light directly into electrical energy. Also called a solar cell.

Photovoltaic Device

A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semiconductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multicrystalline, or amorphous forms.

Photovoltaic Effect

The phenomenon that occurs when photons, the "particles" in a beam of light, knock electrons loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow in one direction across a junction, setting up a voltage. With the addition of circuitry, current will flow and electric power will be available.

Photovoltaic Module

The smallest environmentally protected, essentially planar assembly of photovoltaic cells and ancillary parts, such as interconnections, terminals, and protective devices such as diodes intended to generate direct current power under unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate).

Physical Vapor Deposition

A method of depositing thin semiconductor photovoltaic films. With this method, physical processes, such as thermal evaporation or bombardment of ions, are used to deposit elemental semiconductor material on a substrate.

Pixel

The pixel (from "picture element") is the basic unit of programmable color on a computer display or in a computer image.

Planoconcave

Flat or plane on one side and rounded (concave) on the other, such that the edges are thicker than the center.

Planoconvex

Flat or plane on one side and rounded on the other, such that the center is thicker than the edges.

Polarimeter

an instrument used to measure the rotation of the plane of polarized light as it passes through a sample of an optically active material.

Polarize

To cause the electrical and magnetic fields associated with electromagnetic waves, especially light, to vibrate in a particular direction or path. The transverse electric and magnetic waves always vibrate at right angles to each other, but in ordinary unpolarized light sources, the direction of polarization of each wave is randomly distributed. Light can be polarized by reflection, and by passing through certain materials.

Polychromatic

Refers to multiple wavelengths as opposed to monochromatic, which refers to only one specific wavelength. Sunlight is an example of polychromatic light.

Polycrystalline Silicon

Also known as semicrystalline silicon, polysilicon, poly-Si, or simply "poly", is a material used to make photovoltaic cells, which consists of many variously orientedsilicon crystals, unlike single-crystal silicon. Polycrystalline cells can be recognized by a visible grain in the silicon, a "metal flake effect".

Prism

Optical device having a triangular shape and made of glass or quartz; used to deviate a beam or invert an image.

Progressive Scan

An image scanning method in which the sensor scans each lines of the field sequentially (rows 1, 2, 3, 4..., etc.). All image data is recorded in a single exposure making progressive scanning ideal for high speed applications. See also interlaced scan.

Pyranometer

An instrument used for measuring global solar irradiance.

Pyrheliometer

An instrument used for measuring direct beam solar irradiance. Uses an aperture of 5.7° to transcribe the solar disc.

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Q

Quantum Dot

A nano-scale crystal of semiconductor material composed of various chemical compounds such as zinc sulphide, lead sulphide, cadmium selenide and indium phosphide. These "nanoparticles" react to light by absorbing it and then emitting their own light a couple of nanoseconds later.

Quantum Efficiency (QE)

The ability of a detector to convert photons into electrons. It is the ratio of generated electrons to incident photons expressed as a percentage.

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R

Radiography

Photography that uses radiation other than visible light.

Radiometer

An instrument that measures irradiance of invisible light levels, expressed in Watts per square centimeter (W/cm2)

Recombination

The action of a free electron falling back into a hole. Recombination processes are either radiative, where the energy of recombination results in the emission of a photon, or nonradiative, where the energy of recombination is given to a second electron which then relaxes back to its original energy by emitting phonons. Recombination can take place in the bulk of the semiconductor, at the surfaces, in the junction region, at defects, or between interfaces.

Reflectance

The ratio of the total amount of radiation (light), reflected by a surface to the total amount of radiation incident on the surface.

Reflectometer

An optical instrument used to measure the reflectance of a surface.

Refract

To cause light to change direction as a result of entering a diffrent medium.

Refractive Index

The ratio of the speed of light in air or vacuum to that in another medium.

Refractometer

An optical instrument used to measure the refractive index of a substance.

Resistance

The property of a conductor, which opposes the flow of an electric current resulting in the generation of heat in the conducting material. The measure of the resistance of a given conductor is the electromotive force needed for a unit current flow. The unit of resistance is ohms.

Retardance

The degree of angular shift in the phase of incoming polarized light.

Reticle

A gridwork or lattice of lines set into the eyepiece of optical instruments to help with measurements or alignment.

RGB (Red, Green, Blue)

The basic components of color television system, also the primary colors of light. See also CMYK.

RMS (Root Mean Square)

The square root of the average square of the instantaneous values of an AC output. For a sine wave the RMS value is 0.707 times the peak value. The equivalent value of alternating current, I (electric current), that will produce the same heating in a conductor with resistance, R, as a DC current of value I.

RoHS (Restriction of Hazardous Substances Directive)

The European Union directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment (commonly referred to as the Restriction of Hazardous Substances Directive or RoHS). It restricts the use of the six hazardous materials: lead (Pb), mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE) in all electrical and electronic products offered for sale beginning July 1, 2006 in Europe and January 1, 2007 in California.

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S

Semiconductor

Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.

Semicrystalline

See Polycrystalline Silicon.

Siemens Process

A commercial method of making purified silicon.

Silicon

A semi-metallic chemical element that makes an excellent semiconductor material for photovoltaic devices. It crystallizes in face-centered cubic lattice like a diamond. It's commonly found in sand and quartz (as the oxide).

Sine Wave

A waveform corresponding to a single-frequency periodic oscillation that can be mathematically represented as a function of amplitude versus angle in which the value of the curve at any point is equal to the sine of that angle.

Solar Cell

See Photovoltaic Cell.

Solar Constant

The average amount of solar radiation that reaches the earth's upper atmosphere on a surface perpendicular to the sun's rays; equal to 1353 Watts per square meter or 492 Btu per square foot.

Solar Energy

Electromagnetic energy transmitted from the sun (solar radiation). The amount that reaches the earth is equal to one billionth of the total solar energy generated, or the equivalent of about 420 trillion kilowatt-hours.

Solar Insolation

See Insolation.

Solar Irradiance

See Irradiance.

Solar Noon

The time of the day, at a specific location, when the sun reaches its highest, apparent point in the sky; equal to true or due, geographic south.

Solar Spectrum

The total distribution of electromagnetic radiation emanating from the sun. The different regions of the solar spectrum are described by their wavelength range. The visible region extends from about 390 to 780 nanometers (a nanometer is one billionth of one meter). About 99 percent of solar radiation is contained in a wavelength region from 300 nm (ultraviolet) to 3,000 nm (near-infrared). The combined radiation in the wavelength region from 280 nm to 4,000 nm is called the broadband, or total, solar radiation.

Spectrometer

An optical instrument for measuring the absorption of light by chemical substances; typically it will plot a graph of absorption versus wavelength or frequency, and the patterns produced are used to identify the substances present.

Spectroscopy

The study of spectra, especially experimental observation of optical spectra.

Spherical Aberration

The blurring of an image that occurs when light from the margin of a lens or mirror with a spherical surface comes to a shorter focus than light from the central portion. Parallel light rays that pass through the central region of the lens focus farther away than light rays that pass through the edges of the lens. The result is many focal points, which produce a blurry image.

Sputtering

A process used to apply semiconductor material to a substrate by a physical vapor deposition process where high-energy ions are used to bombard elemental sources of semiconductor material, which eject vapors of atoms that are then deposited in thin layers on a substrate.

Square Wave

A waveform that has only two states, (i.e., positive or negative). A square wave contains a large number of harmonics.

Substrate

The underlying layer of material upon which semiconductor material or a photovoltaic cell is applied.

Superconductivity

The abrupt and large increase in electrical conductivity exhibited by some metals as the temperature approaches absolute zero.

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T

Telecentric Lens

A parallax corrective lens maintaining a constant viewing angle at any point across the clear aperture of the objective lens. Because their images have constant magnification and geometry, telecentric lenses are used for metrology applications, when a machine vision system must determine the precise size of objects independently from their position.

Thin-Film

A layer of semiconductor material, such as copper indium diselenide or gallium arsenide, a few microns or less in thickness, used to make photovoltaic cells.

Triplet Lens

A lens with three optical components.

Two-Axis Tracking

A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal).

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U

Ultraviolet

Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.

USB (Universal Serial Bus)

USB was designed to allow multiple computer peripherals to be connected using a single standardized interface and to improve the plug-and-play capabilities by allowing these peripherals to be connected and disconnected without rebooting the computer or turning off the device (i.e. hot-swapping).

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V

Vacuum Evaporation

The deposition of thin films of semiconductor material by the evaporation of elemental sources in a vacuum.

Valence Band

The highest energy band in a semiconductor that can be filled with electrons.

VESA (Video Electronics Standards Association)

An organization to help standardize how Personal Computers implement video technologies. The first standard this organization created was the 800x600 pixel Super VGA (SVGA) display and its software interface. It also defined the VESA Local Bus.

VGA (Video Graphics Array)

A resolution displayed on a monitor of 640 x 480 pixels. Also refers to a 15-pin video graphics port on a personal computer.

Vignetting

A fall-off in illumination of the image. This can occur when the sensor that is used is larger than the specified maximum sensor size of the lens, or can naturally occur due to limitations of the geometry of the system.

Volt

A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.

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W

Wafer

A thin sheet of semiconductor (i.e. photovoltaic material) made by cutting it from a single crystal or ingot.

Watt

The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).

Waveform

The shape of the phase power at a certain frequency and amplitude.

Wavelength

The peak-to-peak distance covered by one cycle of an electromagnetic wave. It is inversely related to frequency. The longer the wavelength, the lower the frequency; conversely, the shorter the wavelength, the higher the frequency.

Waveplate

An optical element that exhibits the characteristic of birefringence. Orthogonal components of light that enter a waveplate will experience a relative phase shift upon output. The axes of the material exhibit different index characteristics and are generally referred to as the fast (low index) and slow (high index) axes.

WEEE (Waste Electrical and Electronic Equipment)

The European Union directive (2002/96/EC) making manufacturers responsible for financing the recycling of end-of-life equipment.

White Balance

A function in cameras that allows for calibration of colors in different lighting conditions using a reference white.

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X

X-Ray

A form of electromagnetic radiation having wavelengths in the range of approximately 0.1-10 nm, similar to light but of shorter wavelength and capable of penetrating solids and of ionizing gases.

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Y

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Z

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