Glossary of Lighting Terms

  • Foot-Candle
    is the amount of light reaching a object. The commonly used unit of measurement of lighting level (illumination) is the foot-candle (fc). The international unit of measurement of lighting level (Illumination) is the lux (lx). The relationship between the lux and the foot-candle is 1 fc = 10.76 lux.
  • General Lighting
    is substantially uniform lighting of a space without providing for special local lighting requirements like task lighting or accent lighting.
  • Glare
    direct glare is caused by light coming directly to the eye from a light source. Indirect glare is light reflected from a surface in the direction of the eye. Both can harm vision and cause visual discomfort or disability.
  • Halogen Lamp

    a type of incandescent lamp that contains halogen gases (such as iodine, chlorine, bromine, and fluorine), which slow the evaporation of the tungsten filament. Also, sometimes called a tungsten halogen lamp or a quartz lamp.

    HID Lamp

    high intensity discharge (HID) lamps have a longer life and provide more light (lumens) per watt than most other light sources. Available in mercury vapor, metal halide, high pressure sodium, and low pressure sodium types.


    Illuminance (E )is the ratio beetween thaw luminous flux and the area to illuminated. Unit :lm/sq.m

    Incandescent Lamp

    A light source which generates light using a thin filament wire (usually tungsten) heated to white heat by an electric current passing through it.

    Instant Start Ballast

    A type of fluorescent lamp-ballast circuit designed to start fluorescent lamps as soon as the power is applied. Originally, instant-start circuits were developed to eliminate separate mechanical starter devices.
    Inverse Square Law is a law that states that the illuminance (E) at a point on a plane perpendicular to the line joining the point and a source is inversely proportional to the square of the distance (d) between the source and the plane, E = I/d2

    Kilowatt Hour (kwh)

    The standard measure of electrical energy and the typical billing unit used by electrical utilities for electricity. A 100-watt lamp operated for 10 hours consumes 1000 watt-hours (100*10) or 1 kilowatt-hour.

    Luminance (L)

    In a given direction,at a given point of a real or imaginary surface.
    Quotient of the luminous flux transmitted by an elementary beam passing through the given point and propagating in the solid angle containing the solid angle, the area of the section of that beam containing the given point, and the angle between the normal to that section and the direction of the beam. Unit: cd / sq. m

  • Luminous Flux
    indicates all the radiated power emitted by a light source in all directions. Evaluated at spectral eye sensitivity. Unit of measurement: LUMIN [lm].
  • Luminous Intensity
    A light source generally emits its luminous flux F in different directions.Luminous intensity is the luminous flux emitted through unit solid angle.(1 Steradian) in a particular direction. Unit of measurement: CANDELA [cd]
  • Luminaire

    A complete lighting unit consisting of a lamp (or lamps), ballast (or ballasts) as required together with the all necessary parts designed to emit / produce and distribute the light. Also position and protect the lamp & accessories and connect them to the power supply.

  • Luminaire Efficiency
    The ratio of total lumens emitted by a luminaire to those emitted by the lamp or lamps used.
  • Layers of Light
    Layers of light in a given space are created by introducing task lighting (lighting by which people perform tasks), accent lighting (lighting used to highlight specific objects), decorative lighting (lighting created by very attractive light sources), and ambient lighting (lighting that fills the space).
  • Louver
    A type of “screen” made of translucent or opaque material and geometrically designed to prevent lamps from being viewed directly within a given angle. Louvers are intended to minimize direct or indirect glare.
  • MR16 Lamp

    A halogen reflector lamp that measures 16/8 inches in diameter and which directs a sharp, well-defined beam of light.

    MR11 Lamp

    A halogen reflector lamp that measures 11/8 inches in diameter and which directs a sharp, well-defined beam of light.

  • Neodymium
    A rare earth element discovered in 1885 with an atomic number of 60 in the Periodic Table of Elements. It is a fairly common silvery metal that is used to make slightly purple glass envelopes for incandescent light bulbs, eye protection goggles for welding and glass blowing, laser rods, filters to color correct light for art displays, and lenses used by astronomers to calibrate spectrometers,optical instruments used for analysing light.
  • Opaque
    A term that describes a material that does NOT transmit ANY visible light.

  • Power Factor

    In an electrical circuit,is the ratio of the Power in Watts to the product of the r.m.s values of voltage and current for sinusoidal waveforms. It is equal to the cosine of the angle of phase difference between voltage and current.

  • Rapid Start Ballast
    A fluorescent lamp-ballast circuit which uses continuous cathode heating, while the system is energized, to start and maintain lamp light output at efficient levels. Rapid start ballasts may be either electromagnetic, electronic or of hybrid designs. Full-range fluorescent lamp dimming is only possible with rapid start systems.
  • Rated Life
    The rated life of a lamp signifies the time at which 50% of a large quantity of these lamps will have burned out. That means that 50% of these lamps will burn out BEFORE the rated life and 50% will burn out AFTER the rated life. The rated life does NOT mean that every one of the lamps will last at least that long. Also, please note that the Actual Life of a Lamp = the Rated Life of that Lamp x (Rated Voltage/Operating Voltage) raised to the 12th power. For example, the Actual Life of a certain Lamp that is designed to be used with 130 volts is equal to the Rated Life of that Lamp (let’s say 1000 hours) x (130 volts/ 120 volts) raised to the 12th power. The Actual Life of this Lamp is, therefore, equal to (1000 hours) x (1.083) raised to the twelfth power = (1000 hours) x (2.61) = 2610 hours. That means that an incandescent lamp that has a rated life of 1000 hours and is designed to be used 130 volts BUT is used with 120 volts instead will have an “Actual Life” of 2610 hours.
  • Starter
    an electrical device used in conjunction with a ballast for the purpose of starting an electric discharge lamp like a fluorescent lamp or an HID lamp.
  • Task Lighting
    lighting that is specifically installed to light an area where a task is performed.
  • Troffer
    a large recessed luminaire (light fixture) usually installed with the opening flush with the ceiling.
  • Total Harmonic Distortion (THD)
    A measure (in percent) of power quality. THD indicates the distortion of the alternating current wave form. Low values (<20%) are preferred.
  • Voltage
    the difference in electrical charge between two points in a circuit expressed in volts; the electric pressure that exists between two points and is capable of producing a flow of current when a closed circuit is connected between the two points; the rate at which energy is drawn from a source that produces a flow of electricity in a circuit; synonyms: electrical potential, electromotive force, EMF; Formulae: volts = amps x ohms, V = I x R, voltage = electrical current x electrical resistance.
  • Voltage Drop
    the loss of voltage caused by the electrical resistance of the wire and the light fixtures in the circuit. It can become especially noticeable in low voltage circuits (where the operating voltage is 12 or 24 volts). Voltage drop may be minimized by using a thicker wire with a lower gauge wire, shortening the distance between the low voltage transformer and the light fixtures, and/or using a DC transformer.
  • Wattage
    the amount of electrical power consumed by a lamp or light fixture measured in “watts”. One watt is equal the power dissipated by 1 ampere of electrical current flowing across a resistance of 1 ohm or the power produced by 1 ampere of electrical current under an electromotive force of 1 volt. One horsepower is equal to 746 watts. Formulae: watts = volts x amps, P = V x I, electrical power = electromotive force x electric current.