Need a refresher on the latest lighting terms from LA’s own self-proclaimed “Light Reverend”?
Lighting Designer and LightShow West speaker, Steven L. Klein IALD, offers his latest iteration of Klein’s Lighting Lingo Glossary.
Directional lighting to emphasize a particular object or to draw attention to a part of the field of view.
The dissipation of light within a surface or medium.
The process by which the eye changes focus from one distance to another.
The process by which the visual system becomes accustomed to more or less light than it was exposed to during an immediately preceding period. It results in a change in the sensitivity of the eye to light.
Alternating Current (AC)
Flow of electricity which cycles or alternates direction many times per second. The number of cycles per second is referred to as frequency. Most common frequency used in this country is 60 Hertz (cycles per second).
One of the material systems for manufacturing LEDs that produce light in the red and amber portions of the visible light spectrum.
The preferred LED (Light Emitting Diode) chip technology containing Aluminum, Indium, Gallium, and Phosphorous to produce red, orange and amber-colors.
A process and originally patented trademark word of the ALCOA CORP, which is an electrochemical brightening of high purity aluminum in the manufacture of aluminum products.
Fill light, general non-specific, background, light in a space.
The unit for measuring rate of flow of electrical current: Current (Amps) = Power (Watts) / Voltage (Volts)
The system defined by the American National Standards Institute for the binning specifications for light emitting diodes.
The opening in the ceiling of a recessed device usually described in terms of size, 3”, 4” etc, and finish such as
specular clear alzak, or satin pewter, or multi-groove baffle, etc.
An opaque or translucent element that serves to shield a light source from direct view at certain angles, or serves to absorb unwanted light.
An auxiliary device consisting of induction windings wound around a metal core and sometimes includes a capacitor for power correction. It is used with fluorescent and HID lamps to provide the necessary starting voltage and to limit the current during operation.
Candlepower distribution which serves to reduce glare and veiling reflections by having its maximum output in the 30 degree to 60 degree zone.
The systematic dividing of distribution of performance parameters (Flux, Wavelength or CCT, and Vf) in to small finite groupings that may be selected to optimize assembly performance.
Black Body / Black Body Radiator
An object that absorbs all electromagnetic radiation falling on it. Because it reflects no light, a black body appears black. As a black body is heated to incandescence, it radiates light in a sequence of colors, from red to orange to yellow to white to blue, depending on its temperature. This color sequence describes a curve within a color space, known as the black-body curve.
Black Body Curve
A curve within a color space describing the sequence of colors emitted by a black-body radiator at different temperatures
An electrical circuit running from a service panel having its own overload protection device.
An attribute of visual perception in which a source appears to emit a given amount of light. "Brightness" should be used only for non-quantitative references to physiological sensations and perceptions of light. "Brightness" was formerly used as a synonym for the photometric term "luminance" and (incorrectly) for the radiometric term "radiance."
Lighting slang usually and erroneously used in place of “Lamp”. (Bulbs grow in gardens stupid!)
Lighting slang for the recessed housing portion of a recessed down light.
The unit of measurement of luminous intensity of a light source in a given direction.
Luminous intensity expressed in candelas.
Candlepower Distribution Curve
A curve, generally polar, representing the variation of luminous intensity of a lamp or luminaire in a plane through the light center.
An electric energy storage device which when built into or wired to ballast changes it from low to high power factor.
A number indicating cavity proportions calculated from length, width and height.
Popularly referred to as energy-saving lamps, compact fluorescent lamps have a poor image because of perceived deficiencies in colour, power and speed to full output. but massive improvements have been made in all these areas thanks to substantial investment by the big lamp manufacturers.
See International Commission on Illumination.
CIE 1931 Color Space
A color space created by the International Commission on Illumination (CIE) in 1931 to define the entire gamut of colors visible to the average viewer.
CIE Chromaticity Diagram
A horseshoe shaped line connecting the chromaticities of the spectrum of colors. (See Color Definition, Chroma).
To refer to the genetically fixed inner autonomous rhythmnicity the term ‘Circadian Rhythm’ has been coined from two Latin words: ‘circa’ meaning approximately, and ‘dies’, meaning the day. The hormonal oscillation in response to changes in environmental light and darkness. It is generally accepted that autonomous circadian rhythms exist in all eukaryotic beings.
In principal, each single cell is capable of developing circadian rhythms. In a multicellular organism the circadian rhythms of the individual cells, tissues and organs must be reasonably synchronized with one another and adapted to the diurnal rhythms of their environment. Mammals and humans have developed a circadian system in order to fulfill this task. The system comprises three paired centers in the nervous system, which are connected by crossed and uncrossed nerve paths
the retina, the suprachiasmatic nucleus, and the intergeniculate leaflet.
A safety device to prevent excess current flow, which can be reset once tripped.
Coefficient of Utilization (CU)
The ratio of the luminous flux (lumens) from a luminaire calculated as received on the work-plane to the luminous flux emitted by the luminaire’s lamps alone.
Cold Cathode Lamp
An electric –discharge lamp whose mode of operation is that of a glow discharge.
The color of uniformly illuminated objects described using three terms:
Color Rendering Index (CRI)
Measure of the degree of color shift objects undergo when illuminated by the light source as compared with the color of those same objects when illuminated by a reference source of comparable color temperature.
Color Spectrum / Visible Spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye, typically between 390nm and 750nm.
The absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source. The description used to describe the effect of heating an object until it glows incandescently, the emitted radiation, and apparent color, changes proportional to the temperature; easily envisioned when considering hot metal in a forge that glows red, then orange, and then white as the temperature increases.
The transfer of heat through matter by communication of kinetic energy from partical to partical. Example: use of metal such as copper to transfer heat. (See Heat Sink)
Conformal Phosphor Coating
Phosphor application process that uniformly coats the LED chip with phosphor.
A device that controls the output of color-changing and tunable white lighting fixtures. Controllers typically have software components for configuring fixtures and designing and editing light shows, and hardware components for sending control data to fixtures.
The difference in brightness (luminance) of an object and its background.
The transfer of heat through the circulatory motion in a fluid (liquid or gas) at a non-uniform temperature. (Example
air flow over a car radiator)
Cool Beam Lamps
Incandescent PAR lamps that use a special coating (di-chroic interference filter) on the reflectorized portion of the bulb to allow heat to pass out in the back while reflecting only visible energy to the task, thereby providing a “cool beam” of light. Predecessor to the MR16 series of di-chroic lamps.
Correlated Color Temperature The absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source. Usually specified in Kelvin (K). The lower the Kelvin temperature, the warmer the light feels, or appears.
See Color Rendering Index.
Outdoor luminaires that restrict all light output to below 85 degrees from vertical.
The angle at which a lamp is not directly visible in a reflector.
Dali is the Digital addressable Lighting interface is a protocol for lighting controls and dimming agreed by major manufacturers. it is set out in the technical standard iEc 62386. The aG-Dali is a working group set up by the manufacturers and institutions to promote Dali technology and applications.
The amount of light a lighting fixture or lighting installation delivers to a target area or task surface, measured in footcandles (fc) or lux (lx).
Llight emitting semiconductor Chip.
An object with irregularities on a surface causing scattered reflections.
Digital Addressable Lighting Interface (DALI)
A digital communications protocol for controlling and dimming lighting fixtures, originally developed in Europe.
Special fluorescent lamp ballast, which when used with a dimmer control, permits varying light output.
A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material (Carbon, Silicon, Gallium, Geranium, Arsenic) with a p-n junction connected to two electrical terminals. The most common function of a diode is to allow an electric current to pass in one direction (called the diode’s forward direction), while blocking current in the opposite direction (the reverse direction). Today most diodes are made of silicon.
Direct Current (DC)
Flow of electricity continuously in one direction from positive to negative.
Glare resulting from high luminances or insufficiently shielded light sources in the field of view. It usually is associated with bright areas, such as luminaries, ceilings and windows which are outside the visual task or region being viewed.
Direct-View Lighting Fixtures
Lighting fixtures intended for viewing, rather than for illumination. For example, arrays of direct-view fixtures or nodes are used in large-scale video displays, traffic signals, and signage applications.
A lamp in which light (or radiant energy near the visible spectrum) is produced by the passage of an electric current through a vapor or a gas.
Glare producing discomfort. It does not necessarily interfere with visual performance of visibility.
A digital communications protocol for controlling lighting fixtures, originally developed to control stage lighting.
An ambient illumination technique using luminaries that are mounted on or in the ceiling.
Electronics used to power illumination sources.
See Lamp Efficacy.
See Luminaire Efficiency.
An electronic low voltage dimmer, used to dim LED lighting fixtures with electronic transformers.
Equivalent Sphere Illumination (ESI)
The level of sphere illumination that would produce task visibility equivalent to that produced by a specific lighting environment.
Caused by factors inside the organism.
Organic polymer frequently used for a dome or lens, often prone to optical decay over time, resulting in poor lumen maintenance. High quality LEDs contain no epoxy in the optical system and deliver superior lumen maintenance.
An organism in which the cells have a distinct nucleus containing genetic material and separated from cytoplasm by a nuclear membrane. Examples
Protozoa, plants, animals, human beings.
Extended Life Lamps
Incandescent lamps that have an average rated life of 2500 or more hours and reduced light output compared to standard general service lamps of the same wattage.
Plastic or glass fibers of clear optical quality such that light entering one end of it can be transmitted to the other end by the process of ‘total internal reflection’ (TIR).
A system designed for lighting a scene or object to a luminance greater than its surroundings. It may be for utility advertising or decorative purposes.
A low-pressure mercury electric-discharge lamp in which a fluorescing coating (phosphor) transforms some of the ultraviolet energy generated by the discharge into light.
Flux / Luminous Flux
Luminous flux is the measure of the perceived power of light, adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.
The unit of illuminance when the foot is taken as the unit of length. It is the illuminance on a surface one square foot in area on which there is a uniformly distributed flux of one lumen.
Foot Lambert (fl)
A unit of luminance of a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square foot.
A widely accepted printed circuit board (PCB) material which is fiberglass reinforced epoxy laminates that are flame retardant.
Freedom From Binning
Describes the case where the entire production of white LEDs can be described by a single CCT and within a declared number of MacAdam ellipses. No subdivision or color binning of the LEDs is required for use in the intended application.
Replaceable safety device to prevent excess current flow.
See Ambient Lighting.
An effect that occurs when lighting fixtures in the OFF state faintly glow as a result of residual voltage in the circuit.
A photometric device for testing the luminous intensity distribution, efficiency, and luminous flux of luminaires.
A lighting of vertical surfaces technique where the light source is placed close to a textures surface for the express purpose of raising texture in the vertical surface, and drawing attention to it.
The sensation produced by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted to cause annoyance, discomfort, or loss in visual performance and visibility.
Flexible metallic tubing for the protective enclosure of electric wires.
Connection of electrical components to earth for safety.
Relamping of a group of luminaries at one time to reduce relamping labor costs.
The process of removing heat from a luminaire by passing return air through the lamp cavity.
A part of the thermal system that conducts or convects heat away from sensitive components, such as LEDs and electronics.
High-brightness is a term that is often applied to an LED but has no measured meaning and does not indicate any level of performance.
High Intensity Discharge (HID) Lamp
A discharge lamp in which the light producing arc is stabilized by wall temperature, and the arc tube has a bulb wall loading in excess of three watts per square centimeter. HID lamps include groups of lamps known as mercury, metal halide, and high-pressure sodium.
High Output Fluorescent Lamp
Operates at 800 or more milliamperes for higher light output than standard fluorescent lamp (430MA).
High Power LED
A high power LED, sometimes referred to as a power LED, is one that is driven at a current of 350 mA or higher.
High Pressure Sodium (HPS) Lamp
High intensity discharge (HID) lamp in which light is produced by radiation from sodium vapor. This includes clear and diffuse-coated lamps.
Hot / Cold Factor
The relative light output performance at a temperature compared to the light output at a nominal or test temperature. For LUXEON products this is the relative light output at 100C Tj compared to 25C Tj. For “Hot Tested” products like LUXEON A it is the relative light output at 100C Tj compared to 85C Tj.
LED performance testing and specification at an elevated temperature of 85°C.
The intensity of light falling on a surface area. If the area is measured in square feet, the unit of illuminance is footcandles (fc). If measured in square meters, the unit of illuminance is lux (lx).
Illuminating Engineering Society of North America (IES)
The recognized technical authority on illumination, communicating information on all aspects of good lighting practice to its members, to the lighting community, and to consumers through a variety of programs, publications, and services.
Inboard Power Integration
An approach to power management that integrates the power supply directly into a fixture’s circuitry, creating an efficient power stage that consolidates line voltage conversion and LED current regulation.
A lamp in which light is produced by a filament heated to incandescence by an electric current.
Electromagnetic radiation with wavelength range from 700 nm – 3000 nm.
The preferred LED (Light Emitting Diode) semiconductor material system containing Indium, Gallium, and Nitrogen to produce green, blue and white-colored LED light sources.
Intergeniculate Leaflet (IGL)
The retina and the suprachiasmatic nucleus are connected to each other via this additional neural pathway. Nerve fibers extend via the optic nerve to the IGL, a center located in the lateral geniculate body. Nerve fibers from the IGL reach the suprachiasmatic nucleus via the geniculohypothalamic tract. It is assumed that zeitgebers of the circadian systems other than light also influence the suprachiasmatic nucleus via this path.
A device used for a variety of optical, photometric, or radiometric measurements.
Inverse Square Law
The law stating that the illuminance at a point on a surface varies directly with the intensity of a point source and inversely as the square of the distance between the source and the point. If the surface at the point is normal to the direction of the incident light, the law is expressed by Fc=CP / D (squared).
An IP (index of protection) rating tells you the level of protection that a luminaire or other piece of equipment provides against things getting in – including dust, dirt and water as well as hands and fingers. For example, a fitting rated IP22 is protected against insertion of fingers and will not be damaged by exposure to dripping water.
A series of lines plotted on any appropriate set of coordinates, each line connecting all the points on a surface having the same illumination.
A metal box in which circuit wiring is spliced. It may also be used for mounting luminaries, switches or receptacles.
Junction temperature, noted as Tj, is the temperature of the LED’s active region.
Term and symbol (K) used to indicate the comparative color appearance of a light source when compared to a theoretical blackbody. Yellowish incandescent lamps are 3000K. Fluorescent light sources range from 3000K to 7500K and higher.
Unit of electrical power consumed over a period of time. KWH=watts/1000xhours used.
An artificial source of light (also a portable luminaire equipped with a cord and plug).
The ratio of lumens produced by a lamp to the watts consumed. Expressed as lumens per watt (LPW).
Lamp Lumen Depreciation (LLD)
Multiplier factor in illumination calculations for reduction in the light output of a lamp over a period of time.
Electromagnetic radiation energy that is capable of exciting the retina and producing a visual sensation. The visible portion of the electromagnetic spectrum extends from about 380 to 770 nm.
Leading Edge Dimmer
A type of dimmer that regulates power to lamps by delaying the leading edge of each half-cycle of AC power. Compatible with many LED fixtures.
A light emitting diode is a PN (positive/negative) junction opto-semiconductor that emits single-color light when operated in a forward biased direction. This converts electrical energy into visible light energy.
An assembly of LED packages or dies on a printed circuit board or substrate, possibly with optical elements and additional thermal, mechanical, and electrical interfaces that are intended to connect to the load side of an LED driver.
LED Chip (Chip)
The light producing semiconductor device that may or may not be incorporated into an LED.
An electronic circuit that converts input power into a current source — a source in which current remains constant despite fluctuations in voltage. An LED driver protects LEDs from normal voltage fluctuations, overvoltages, and voltage spikes.
LED Light Engine
An integrated assembly comprised of LEDs or LED arrays, LED driver, and other optical, thermal, mechanical, and electrical components.
A complete lighting unit consisting of LED-based light emitting elements and a matched driver together with parts to distribut light, to position and protect the light emitting elements, and to connect the unit to a branch circuit. The LED based light emitting elements may take the form of LED packages, (components), LED arrays (modules) LED Light Engine, or LED lamps. The LED luminaire is intended to connect directly to a branch circuit.
See LED array.
Life Performance Curve
A curve that represents the cvariation of a particular characteristic of a light source (such as luminous flux, intensity , etc.) throughout the life of a source. Also referred to as Lumen Maintenance curve)
Light Emitting Diode (LED)
A Light Emitting Diode (LED) is a solid-state semiconductor device that converts electrical energy directly into light. On its most basic level, the semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.
Used in luminaries to redirect light into useful zones.
Lighting designed to provide illuminance over a relatively small area or confined space without providing any significant general surrounding lighting.
A series of baffles used to shield a source from view at certain angles or to absorb unwanted light. The baffles usually are arranged in a geometric pattern.
Long Life Lamps
See Extended Life Lamps.
Low Pressure Sodium Lamp
A discharge lamp in which light is produced by radiation of sodium vapor at low pressure producing a single wavelength of visible energy, i.e., yellow.
Low Voltage Lamps
Incandescent lamps that operate at 6 to 12 volts.
The unit of luminous flux. It is the luminous flux emitted within a unit solid angle (one steradian) by a point source having a uniform luminous intensity of one candela.
Describes the percentage of light lost relative to the initial lumen output. See lumen maintenance for more information.
The luminous flux at a give time in the life of the LED. This is expressed as a percentage of the intial luminous flux.
Lumen Maintenance Curve
A graph illustrating the predicted average light output behavior over time of a single LED or solution.
The total lumens emitted of a light source, system, or solution.
A complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps and to connect the lamps to the power supply.
Luminaire Dirt Depreciation (LDD)
The multiplier to be used in illuminance calculations to relate the initial illuminance provided by clean, new luminaries to the reduced illuminance that they will provide due to dirt collection on the luminaries at the time at which it is anticipated that cleaning procedures will be instituted.
The ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein.
The amount of light reflected or transmitted by an object.
Light output of a source divided by nominal wattage, given in lumens per watt (lm/W).
Often used as an objective measure of the useful power emitted by a light source.
This Philips proprietary phosphor system embeds phosphor in a ceramic platelet that can be mass manufactured with very high degrees of uniformity and consistency.
The metric unit of illuminance. One lux is one lumen per square meter (lm/m). Lux is the international unit of illuminance – a measure of how much luminous flux (in lumens) is spread over a given area (in square metres). In other words, it tells you how much light is arriving at a surface. 1 lm/m2 equals 1 lx. Multiply an illuminance figure in lux by an amount of time in hours and you have a measure of exposure in lux hours – useful if you’re looking after delicate objects or surfaces that can’t be exposed to too much light.
A MacAdam ellipse is the region on a chromaticity diagram which contains all colors which are indistinguishable, to the average human eye, from the color at the center of the ellipse.
Maintenance Factor (MF)
A factor used in calculating illuminance after a given period of time and under given condition. It takes into account temperature and voltage variations, dirt accumulation on luminaire and room surfaces, lamp depreciation, maintenance procedures and atmosphere conditions.
The material, such as aluminum indium gallium phosphide (AlInGaP) and indium gallium nitride (InGaN), used within an LED to produce light of a specific color.
A high intensity discharge (HID) lamp in which the major portion of the light is produced by radiation from mercury. Includes clear, phosphor-coated and self-ballasted lamps.
Metal Halide Lamp
A high intensity discharge (HID) lamp in which the major portion of the light is produced by radiation of metal halides and their products of dissociation-possibly in combination with metallic vapors such as mercury. Includes clear and phosphor coated lamps.
Vertically downward directly below the luminaire or lamp; designated as 0 degrees.
One billionth (10-9) of a meter, or ten Ångstroms.
Luminous tubes that light up when ions of neon gas are excited by the passing of an electric arc. Noble gasses found in the section 7a of the Periodic chart.
Measurement of display screen brightness. 1 nit = 1 cd/m2.
NTSC Color Space
The range of colors within the CIE Chromaticity Diagram included when combining phosphor based RGB sources in CRTs such a televisions and computer monitors.
The difference between lamp cut off and visual cut-off. If a reflector produces light at an angle greater than the shielding angle, the light is in the offending zone.
Onboard Power Integration
An approach to power management that integrates the power supply into a fixture’s housing, eliminating the need for an external power supply.
Organic Light-emitting Diodes (OLED)
Organic light-emitting diodes (OLEDs) are based on organic (carbon based) materials. In contrast to LEDs, which are small point sources, OLEDs are made in sheets which provide a diffuse area light source. OLED technology is developing rapidly and is increasingly used in display applications such as cell phones and PDA screens. However, OLEDs are still some years away from becoming a practical general illumination source. Additional advancements are needed in light output, color, efficiency, cost, and lifetime.
See Junction Box.
Parabolic Aluminized Reflector lamps which offer excellent beam control, come in a variety of beam patterns from very narrow spot to wide flood, and can be used outdoors unprotected because they are made of “hard” glass that can withstand adverse weather.
A grid of baffles that redirect light downward and provide very low luminaire brightness.
PC Amber (Phosphor Converted)
PC amber is a method of making amber colored LEDs from royal blue LED chips. It requires the use of special phosphors and results in a more reliable, less temperature sensitive, and more consistent amber LED.
A coating of phosphorescent material which photons from a royal blue LED pass through causing those photons to exit with a different color property.
This is the process by which photons from an LED chip are converted to a different color. White LEDs and some colored LEDs are made using phosphor conversion.
The science of measuring visible light in units that are weighted according to the sensitivity of the human eye. It is a quantitative science based on a statistical model of the human visual response to light. In other words, human perception of light under carefully controlled conditions.
is a process by which light is converted into electrical signals in the rod cells, cone cells and photosensitive ganglion cells of the retina of the eye. It is divided into an activation process and an inactivation process.
Planckian Black Body Locus
The line on the CIE Chromaticity Diagram that describes the color temperature of an object when heated from approximately 1,000K to more than 10,000K.
Area on an LED chip where the positively and negatively charged regions meet. When current is applied, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths. In short, the area on a chip where light is produced.
Point Method Lighting Calculation
A lighting design procedure for predetermining the illuminance at various locations in lighting installations, by use of luminaire photometric data.
The process by which the transverse vibrations of light waves are oriented in a specific plane. Polarization may be obtained by using either transmitting or reflecting media.
The active power divided by the apparent power (i.e., product of the rms input voltage and rms input current of a driver).
Ratio of watts over volts times amperes. Power factor in lighting is primarily applicable to ballasts. Since volts and watts are usually fixed, amperes (or current) will go up as power factor goes down. This necessitates the use of larger wire sizes to carry the increased amount of current needed with Low Power Factor (L.P.F.) ballasts. The addition of a capacitor to L.P.F. ballast converts it to H.P.F. ballast.
Power Factor Correction
In an electronic device, such as an LED lighting fixture, a system of inductors, capacitors, or voltage converters to adjust the power factor of electronic devices toward the ideal power factor of 1.0.
Preheat Fluorescent Lamp
A fluorescent lamp designed for operation in a circuit requiring a manual or automatic starting switch to preheat the electrodes in order to start the arc.
In a diode’s p-n semiconductor junction, p-type material is positively charged. Atoms in the p-type material have electron holes — electrons missing from their outer rings.
Pulse Width Modulation (PWM)
A method, used by LED drivers, to regulate the amount of energy to the LEDs. PWM turns LEDs on and off at high frequency, reducing total ON time to achieve a desired dimming level.
Reflectorized lamps available tin spot (clear face) and flood (frosted face).
Energy transmitted through electromagnetic waves. (Ex: Heat radiated by the sun and by incandescent lamps.)
The total energy emitted by a light source across all wavelengths, measured in watts.
The field that studies the measurement of electromagnetic radiation, including visible light. Note that light is also measured using the techniques of photometry, which deal with brightness as perceived by the human eye, rather than absolute power.
Radiance and spectral radiance
Radiometric measures that describe the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle in a specified direction. They are used to characterize both emission from diffuse sources and reflection from diffuse surfaces. The SI unit of radiance is watts per steradian per square meter (W·sr-1·m-2). Radiance characterizes total emission or reflection, while spectral radiance characterizes the light at a single wavelength or frequency.
Rapid Start Fluorescent Lamp
A fluorescent lamp designed for operation with ballast that provides a low-voltage winding for preheating the electrodes and initiating the arc without a starting switch or the application of high voltage.
Light bouncing off a surface. In specular reflection, the light strikes and leaves a surface at the same angle. Diffuse reflected light leaves a surface in all directions.
Sometimes called reflectance factor. The ratio of reflected light to incident light (light falling on a surface). Reflectance is generally expressed in percent.
Glare resulting from specular reflections of high luminances in polished or glossy surfaces in the field of view. It usually is associated with reflections from within a visual task or areas in close proximity to the region being viewed.
A phosphor conversion technique in which photons from a royal blue LED pass through a phosphor material that is not attached to the LED chip.
Second of three centers of the circadian system, the retina of the eye phylogenetically forms part of the diencephalons. There are indications that the circadian system in the retina may process its own receptor and processing structures. The suprachiasmatic nucleus receives information from the retina via the retinohypothalamic tract to synchronize the circadian rhythm with the day-night cycle.
The process by which the direction of a ray of light changes as it passes obliquely from one medium to another in which its speed is different.
RGB Color Model
An additive color model in which red, green, and blue light are added together in different proportions to produce a broad range of colors, including white.
A method of producing white light by combining the output from red, green, and blue LEDs.
Also known as "visual purple" it is a vertebrate class of G-Protein coupled photoreceptors. It is a pigment of the retina that is responsible for the first events in the perception of light.
A cable comprised of flexible plastic sheathing inside of which are two or more insulated wires for carrying electricity.
Room Cavity Ratio (RCR)
A number indicating room cavity proportions calculated from length, width and height.
Rough Service Lamps
Incandescent lamps designed with extra filament supports to withstand bumps, shocks and vibrations with some loss in lumen output.
See standard deviation of color matching.
A semiconductor has electrical conductivity intermediate to that of a conductor and an insulator. Semiconductors differ from metals in their characteristic property of decreasing electrical resistivity with increasing temperature. Carbon and germanium (germanium, like silicon, is also a semiconductor) have a unique property in their electron structure: Each has four electrons in its outer orbital. This allows them to form nice crystals. The four electrons form perfect covalent bonds with four neighboring atoms, creating a lattice. While silicon crystals look metallic, they are not, in fact, metals. All of the outer electrons in a silicon crystal are involved in perfect covalent bonds, so they can’t move around. A pure silicon crystal is nearly an insulator — very little electricity will flow through it. Semiconductor materials are useful because their behavior can be manipulated by the addition of impurities, known as doping. The comprehensive theory of semiconductors relies on the principles of quantum physics to explain the motions of electrons through a lattice of atoms. (see P/N Junction)
Lighting slang meaning elliptical beam signature as seen on a vertical surface.
A series of overlapping elliptical beam signatures. A symmetrical wall-wash technique when multiples are grouped.
Determining the quality of a reflector, it is the angle at which lamp and lamp image in a reflector are the same.
A description of the devices that do not contain moving parts or parts that can break, rupture, shatter, leak or contaminate the environment.
Spectral Luminous Efficiency Function
A bell-shaped curve describing the sensitivity of a human eye with normal vision to the spectrum of visible light. Also known as the eye-sensitivity
Standard deviation of color matching (SDCM)
Describes the difference between two colors. A difference of one to three SDCM “steps” is virtually imperceptible, a difference of four SDCM steps is just noticeable, and a difference of more than four SDCM steps is readily visible.
Sound Transmission Class (STC)
A number rating system for room-to-room sound transmission through air handling luminaries. The higher the STC number, the lower the level of sound transmission.
Ratio of the distance between luminaire centers to the mounting height above the work-plane for uniform illumination.
Spectral Energy Distribution (SED) Curves
A plot of the level of energy at each wavelength of a light source.
The illumination on a task from a source providing equal luminance in all directions about that task, such as an illuminated sphere with the task located at the center.
The standard unit of solid angle. Describes two-dimensional angular spans in three-dimensional space.
Subtractive Color Model
A color model that applies to reflective surfaces such as paints, dyes, and inks. Combining red, green, and blue in equal amounts produces black.
Suprachiasmatic nucleus (SCN)
A small accumulation of nerve cells in the hypothalamus, the SCN is located directly above the optic chiasma and is considered to be the circadian pacemaker (or inner clock).
Lighting directed to a specific surface or area that provides illumination for visual tasks.
Controlling the operating temperature of the product through design, examples includes heat sinks and improved airflow.
Thermal Pad Temperature
The measured temperature of the thermal pad during tesing. The thermal pad aides in the conduction of heat away from the component being cooled and into the heatsink. For more information refer to LUXEON® Rebel and LUXEON® Rebel ES Assemby and Handling Guide application brief 32.
This technology refers to an LED package using a lead frame to provide electrical connections. Typical thru-hole LEDs are three and five millimeters in diameter and have a narrow viewing angle and low power-handling abilities due to the lack of a dedicated thermal path. Thru-hole LEDs are installed into holes drilled in the printed circuit board (PCB) and are then placed in a wave solder oven to make connections with electrical connections on the bottom side of the circuit board.
Trailing Edge Dimmer
A type of dimmer that regulates power to lamps by delaying the end of each half-cycle of AC power. Compatible with many LED fixtures.
A device to raise or lower electric voltage.
The passage of light through a material.
Tunable White Light
White-light LED fixtures that combine channels of warm white and cool white LEDs to produce a range of color temperatures.
A gas filled tungsten incandescent lamp containing a certain proportion of halogens.
Electromagnetic radiation with wavelength shorter than that of visible light.
The amount of light a lighting fixture delivers in an application, minus any wasted light.
Regular reflections superimposed upon diffuse reflections from an object that partially or totally obscure the details to be seen by reducing the contrast. This is sometimes called reflected glare.
Visual Comfort Probability (VCP)
The rating of a lighting system expressed as a per cent of people who, when viewing from a specified location and in a specified direction, will be expected to find it acceptable in terms of discomfort glare.
The line on an Isolux chart that has a value equal to 10% of the maximum illumination.
The field of view that can be perceived when the head and eyes are kept fixed.
Rods and cones of the retinas of both eyes are the receptors of visual perceptions. The signals of the receptors are pre-processed in the neuronal layers of the retina and passed via the optic nerve and the optical tract to the lateral genticulate body and from there via optic radiation to the occipital cortex of the telecephalon. The nerve fibers from the nasal retinal halves cross in the optic chiasma to the opposite side, while the fibers from the temporal halves of the retinas extend without crossing to the lateral genticulate body.
The unit for measuring electric potential. It defines the force or pressure of electricity.
Wall Plug Efficiency
This typically refers to the effectiveness of converting electrical power to light output. It is defined as the ratio of the radiant flux to the input electrical power.
Wall Wash Lighting
A smooth even distribution of light over a wall.
A description of light with a correlated color temperature between 3000K and 3500K, usually perceived a slightly yellow.
The unit for measuring electric power. It defines the power or energy consumed by an electrical device. The cost of operating an electrical device is determined by the watts it consumes times the hours of use. It is related to volts and amps by the following formula: Watts = Volts x Amps.
is the distance between repeating units of a wave pattern. It is commonly designated by the Greek letter lambda (λ). In a sine wave, the wavelength is the distance between the midpoints of the wave:
The Coordinated Color Temperature (CCT) defined by a line perpendicular to the Planckian Black Body Curve and intersecting the measured chromaticity.
Coined from two German words meaning time-giver, this word refers to external synchronizing factors, such as light, noise, food, exercise, etc.
Zhaga (not an acronym) is an industry-wide co-operation to standardise specifications for the interfaces of LED light engines. The aim is to enable interchangeability between products made by diverse manufacturers by defining interfaces for a variety of application-specific light engines. Currently, all Zhaga members are manufacturers.
Zonal Cavity Method Lighting Calculation
A lighting design procedure used for predetermining the relation between the number and types of lamps or luminaires, the room characteristics, and the average illuminance on the work-plane. It takes into account both direct and reflected flux.