adaptation – The process by which the retina of the eye becomes accustomed to more or less light than it was exposed to during an immediately proceeding period. It results in a change in the sensitivity of the eye to light.
ANSI (American National Standards Institute) – The organization that develops voluntary guidelines and produces standards for the electrical and other industries.
average life – Value for life expectancy of a lamp.
ballast – A device used with an electric-discharge lamp to obtain the necessary circuit conditions (voltage, current and wave form) for starting and operating; all fluorescent and HID light sources require a ballast for proper operation. Dimming ballasts are special ballasts which when used together with a dimmer will vary the light output of a lamp.
ballast factor, BF – The measured ability of a particular ballast to produce light from the lamp(s) it powers. Ballast factor is derived by dividing the lumen output of a particular lamp/ballast combination by the lumen output of the same lamp(s) on a reference ballast.
base – End of the lamp that inserts into the lamp socket.
beam spread – (In any plane) the angle between the two directions in the plane in which the candlepower is equal to a stated percent (usually ten percent) of the maximum candlepower in the beam.
brightness – See luminance.
bulb – Outer jacket or envelope of a lamp.
burning position – Position that lamps are designed to operate.
candlepower distribution – A curve that represents the variation in luminous intensity (expressed in candelas) in a plane through the light center of a lamp or luminaire; each lamp or lamp/luminaire combination has a unique set of candlepower distributions that indicate how light will be spread.
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.
CCT rating – CCT rating is based on operation at rated watts in the designated operating position. For universal lamps, CCT is rated in the vertical position. All other operating positions will lead to higher values of CCT.
center beam candlepower, CBCP – The intensity of light produced at the center of a reflector lamp, expressed in candelas.
chromaticity – The aspect of color that includes consideration of its dominant wavelength and purity.
coefficient of utilization, CU – The ratio of the luminous flux (lumens) from a luminaire received on the work-plane to the lumens emitted by the luminaire’s lamps alone.
color uniformity – Consistency of color from lamp to lamp.
correlated color temperature, CCT – A specification of the color appearance of a lamp relating its color to that of a reference source heated to a particular temperature, measured in degrees Kelvin (K); CCT generally measures the “warmth” or “coolness” of light source appearance.
current, I – A measure of the flow of electricity, expressed in amperes (A).
current crest factor – Ratio of peak to rms value of lamp current: mh values range from 1.4-1.8. Cannot go above 1.8 or it reduces lamp life.
cut-off angle – (Of a luminaire) the angle from the vertical at which a reflector, louver or other shielding device cuts off direct visibility of a light source. It is the complementary angle of the shielding angle.
diffuser – A device to redirect or scatter the light from a source by the process of diffuse transmission.
direct glare – Glare resulting from high luminance or insufficiently shielded light sources in the field of view, or from reflecting areas of high luminance. It is usually associated with bright areas such as luminaires, ceilings and windows that are outside the visual task or region being viewed.
direct lighting – Lighting by luminaires distributing 90 to 100 percent of the emitted light in the general direction of the surface to be illuminated. The term usually refers to light emitted in a downward direction. (See accent lighting.)
disability glare – Glare resulting in reduced visual performance and visibility. It is often accompanied by discomfort.
discharge lamp – Light-producing device that depends on electric arc, rather than filament, to create illumination.
discomfort glare – Glare producing discomfort. It does not necessarily interfere with visual performance or visibility.
double-ended – Lamps that have two bases opposite one another for series electrical connection, mounting connection and heat dissipation.
efficacy – Efficiency of a light source expressed in lumens per watt (LPW or lm/W).
energy – A measure of work done by and electrical system over a given period of time, often expressed in kilowatt-hours (kWh).
enhancing reflections – Reflections which enhance appearance described in such terms as sparkling, glittering, etc.
ESCO – Energy Saving Service Company
filament – A tungsten wire purposely positioned inside a lamp bulb that when heated, electrically generates radiation in the visible, infrared and ultraviolet ranges.
fixture – See luminaire.
floodlight – A reflector lamp with a relatively wide beam pattern.
footcandle, FC – A unit of illuminance equal to 1 lumen per square foot.
formed body arc tube – Arc tube formed by quartz sculpting process, has 1/3 less quartz mass than standard arc tubes, 3rd starter electrode eliminated. Ballast requires external ignitor with 3-4 KV to start lamp.
frequency – The number of times per second that an alternating current system reverses from positive to negative and back to positive, expressed in cycles per second or hertz, Hz.
high intensity discharge (HID) lamps – A general group of lamps consisting of mercury, metal halide and high pressure sodium lamps.
illuminance – Light arriving at a surface, expressed in lumens per unit area; 1 lumen per square foot equals 1 footcandle, while 1 lumen per square meter equals 1 lux.
incandescent filament lamp – A lamp in which light is produced by a filament heated to incandescence by an electric current.
indirect lighting – Lighting by luminaires distributing 90 to 100 percent of the emitted light upward.
infrared radiation, IR – Is a type of electromagnetic radiation given off by incandescent and fluorescent lighting.
initial lumens – The light output of a HID lamp at rated power on a reference ballast after 100 hours of operation.
lamp life – An average rating, in hours, indicating when 50% of a large group of lamps have failed, when operated at nominal lamp voltage and current. Manufacturers use 3 hours per start for fluorescent lamps and 10 hours per start for HID lamps when performing lamp life testing procedures. Every lamp type has a unique mortality curve that depicts its average rated life.
lamp lumen depreciation factor, LLD – The multiplier to be used in illumination calculations to relate the initial rated output of light sources to the anticipated minimum rated output based on the re-lamping program to be used.
lamp voltage – Voltage which lamps operate when they are fully warmed up.
lens – A glass or plastic element used in luminaries to change the direction and control of the distribution of light rays.
level of illumination – See illuminance.
light – Radiant energy that is capable of producing a visual sensation.
light center length, LCL – The distance from the center of the visible arc discharge to the bottom of the contact of the base.
light emitting diode, LED – Semiconductor diodes, electronic devices that permit current flow in only one direction. The diode is formed by bringing two slightly different materials together, forming a junction. When a forward voltage is applied, current flow begins and energy is radiated in the form of light.
light loss factor, LLF – A factor used in calculating illuminance after a given period of time and under given conditions. It takes into account temperature and voltage variations, dirt accumulation on luminaire and room surfaces, lamp depreciation, maintenance procedures and atmosphere conditions. Formerly called maintenance factor.
light on centers, LOC – Distance between LED lights.
lighting design lumens, LDL – Number of lumens at 2,000 hours of operation.
louver – A series of baffles used to shield a source from view at certain angles or to absorb unwanted light. The baffles are usually arranged in a geometric pattern.
lumen, lm – A unit of luminous flux; the overall light output of a luminous source is measured in lumens. Amount of light lamp emits once it’s started.
lumen depreciation – The decrease in lumen output of a light source over time; every lamp type has a unique lumen depreciation curve (sometimes called lumen maintenance curve) depicting the pattern of decreasing light output.
lumen maintenance – Lumen output provided by lamp at given point in, or percentage of, its life.
lumens per watt, LPW – Lumen (light) output divided by lamp watts consumed (i.E. Amount of electricity used); also known as efficacy.
luminaire – A light fixture; the complete lighting unit, including a lamp, reflector ballast, socket, wiring, diffuser, and housing.
luminaire efficiency – The ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein.
luminance, L – Light reflected in a particular direction; the photometric quantity most closely associated with brightness perception, measured in units of luminous intensity (candelas) per unit area (square feet or square meters).
luminance contrast – The relationship between the luminance of and object and its immediate background.
luminance ratio – The ratio between the luminance of any two areas in the visual field.
luminous flux – The time rate of the flow of light.
lux, lx – A unit of illuminance equal to 1 lumen per square meter.
matte surface – A non-glossy, dull surface as opposed to a shiny (specular) surface. Light reflected from a matte surface is diffused.
mili-candela, MCD – The measurement of light output of a LED in thousandths of a candela.
open rated lamp, medium base – Designed for open fixtures; has narrower neck than standard medium base lamps to fit into an exclusionary medium socket for open fixture use.
power factor – A measure of the effectiveness with which an electrical device converts volts-amperes to watts; devices with power factors >0.90 are “high power factor” devices.
reference ballast – A ballast specifically constructed to have certain prescribed characteristics for use in testing electric-discgage lamps and other ballasts.
reflectance, rho – There percentage of light reflected back from a surface, the difference having been absorbed or transmitted by the surface.
reflected glare – Glare resulting from specular reflections of high luminance in polished or glassy surfaces in the field of view.
reflection – The process by which flux leaves a surface or medium from the incident side.
refraction – The process by which the direction of a ray of light changes as it passes obliquely from one medium to another.
refractor – A device used to redirect the luminous flux from a source, primarily by the process of refraction.
resistance, R – A measure of resistance to flow of the current, expressed in ohms.
restrict time – The time to re-ignite the arc of a HID lamp.
shielding angle – The complementary angle of the cut-off angle of a luminaire.
shroud – Glass cylinder surrounding the arc tube to protect against hot arc tube particles from breaking the glass bulb if an arc tube rupture occurs; reduces risk of using mh lamps in open fixtures.
Special (SPC) – Items not stocked in TCP’s warehouse. These items have longer lead times than stocked (STK) items. Contact our customer service department at 800-324-1496 for additional details.
spectral power distribution, SPD – A curve illustrating the distribution of power produced by the lamp, at each wavelength across the spectrum.
spotlight – A reflector lamp with a narrow mean pattern used to illuminate a specifically defined area.
Stocked (STK) – Item is in stock and applicable to standard shipping.
supplementary lighting – Lighting used to provide an additional quantity and quality of illumination that cannot be readily obtained by the general lighting system and that supplements the general lighting level usually for specific task requirements.
Special Order (SPO) – Items marked SPO require a lead time of 4-6 weeks, and utilize a premium delivery option. Contact our customer service department at 800-324-1496 for additional details.
visual comfort probability, VCP – A discomfort glare calculation that predicts the percent of observers positioned in the least favorable part of the room who would be expected to judge a lighting condition to be comfortable. VCP rates the luminaire in its environment, taking into account such factors as illuminance level, room dimensions and reflectances, luminaire type, size and light distribution, number and location of luminaires, and observer location and line of sight. The higher the VCP the more comfortable the lighting environment.
visual field – The location of objects or points in a space where the head and eyes are kept fixed.
visual task – Those details and objects which must be seen for the performance of a given activity, including the immediate background of the details or objects.
voltage, V – A measure of the electrical potential, expressed in volts (V).
watt, W – A unit of electrical power equal to 1 joule per second.