Glossary - lighting matters

Defines the way of pointing or directing an adjustable light. It is calculated always from vertical. For example an aiming angle of 30 degrees is effective for lighting paintings.

The overall lighting in an area or room also known as general lighting.

Opening of a fixture through which light exists and can enter.

A tube enclosed by the outer glass envelope of an HID lamp and made of clear quartz or ceramic that contains the arc stream.

Architectural lighting defined to provide sufficient light for the purposes of illuminating the outside landscape, monument, building as well as balancing factors of initial and operating cost, appearance, and energy efficiency.

Inert gas used in incandescent and fluorescent lamp types. In incandescent light sources, argon slows down evaporation of the filament.

An average rating, in hours, indicating when 50% of a large group of lamps are likely to fail, when operated at nominal lamp voltage and current. Every lamp type has a unique mortality curve that depicts its average rated life which is typically different from the actual life.

The horizontal angular distance between a fixed reference direction and a position contained within a circle in the horizontal plane. Often referenced as the horizontal angles of a candela distribution.

Translucent element used to prevent glare, and control light distribution at certain angles. They are often painted black to absorb light.

That part of the lamp that inserts into a lamp socket.

Clear glass, often with a high lead content, with edges that are cut on an angle to add depth and a glittery appearance.

Hand blown glass is created by blowing air into a molten balloon of glass.

Glass elements held together by metal strips, typically brass or copper; include Leaded Glass, which has a heavier look.

Brightness is a person's subjective attribute of any light sensation giving rise to the perception of luminous magnitude, including the whole scale of qualities of being bright, light, brilliant, dim or dark.

Built-in lighting generally refers to lighting equipment mounted into coves and cornices, behind valences, or integrated into furniture and bookcases.

The everyday term for an incandescent lamp. Also refers to the outer shell of the lamp (See also Incandescent Lamp).

Darkening or discolouration of an incandescent lamp due to tungsten particles collecting on the inside of the glass as the filament burns and diminishes over its life.

Glass consisting of a layer of clear glass fused to a layer of opal or other tinted glass. Cased glass transmits light more efficiently than opal, with more lustre and better diffusion. Cased glass can be blown or moulded.

Pouring or forcing metal or glass into a prepared mould or any part manufactured in this manner.

Metal band encircling the cathode of a fluorescent lamp, used to collect the evaportating particles from the cathode, greatly reducing end-blackening.

A number indicating cavity proportions from length, width and height. This value used in the coefficient of utilisation calculation for a given luminaire in a space with specified room reflectance and dimensions.

A blown glass tube of various shapes placed around flame to protect it against wind. In today’s usage, it is for ornamentation and light diffusion.

The CIE normalised colour system is an attempt by the International Lighting Commision (CIE) to represent colours based on the human colour perception. The direct effect of the human colour reception mechanism forms the basis.

The ratio of the luminous flux () from a luminaire calculated as received on the work-plane to the luminous flux emitted by the luminaire's lamps alone.

A small fluorescent lamp that is often used as an alternative to incandescent lighting. The lamp life is about ten times longer than incandescent lamps and is 3 to 4 times brighter. Also referred to as PLI DL, CFL or BIAX lamps.

The relationship between the luminance of an object and its background.

Light sources mounted above a ledge or in a horizontal recess that distribute light upward for ambient lighting.

Fine quality transparent glass. May be used in table lamps, chandeliers and floor lamps in a variety of styles and cuts.

The angle from a fixture's vertical axis at which a reflector or other shielding device cuts off direct visibility of a lamp. It is the complementary angle of the shielding angle.

Deck lights typically mount to the outside of a home or to the railing of a wooden deck. Since they are located near where people sit, good shielding and proper mounting height are important to reduce glare.

Film that reflects visible light and transmits infrared light. Reflector lamps with dichroic coatings, such as most MR16s provide a cooler beam because most of the heat goes out the back. Dichroic PAR lamps are often called “cool beam.”

Lighting that casts all, or at least 90%, of its light downward. The term can also refer to the distribution of light or the fixtures that produce this type of lighting.

A direct ceiling lighting unit, usually small, can be recessed, where most of the light is directed downward. May feature an open reflector and/or shielding device.

Incandescent lamp with an elliptically-shaped reflector shell. Focuses light immediately in front of the lamp which reduces absorption and increases efficiency.

Darkening around the ends of a fluorescent tube caused by particles evaportating from the cathode and adhering to the glass. Lamps made with cathode guards greatly reduce this occurrence.

Fixture, usually recessed, which can be rotated to point in a desired direction.

Wire used in incandescent lamps, usually made of tungsten and often coiled, that emits light when heated by an electrical current.

In incandescent lamps, usually argon or krypton with trace nitrogen. In fluorescent lamps may be argon. Halogen is used in halogen incandescent lamps.

Luminaire without lamps.

The wide distribution of a reflectorised lamp, abbreviated FL. Also a fixture with a widespread light throw.

Floodlights create a widespread distribution of light, perfect for illuminating a wall, sign or large object. A floodlight should be well shielded to avoid stray light and glare.

A glass tube coated on the inside with a fluorescent substance that gives off light when mecury vapour in the tube is excited by a stream of electrons from the cathode.

Globe-shaped incandescent lamp, generally for exposed use.

Uniform light throughout an area , also known as Ambient lighting. General lighting provides an area with overall, non-specific illumination. General lighting radiates a comfortable level of brightness, enabling one to see and walk about safely. A basic form of lighting that replaces sunlight, general lighting is fundamental to lighting a home.

Glare is the visual perception of interference caused by differences in the light density of the souroundings.

Directional light at an acute angle, which emphasises texture. The sources of grazing light must be close to the surface. See also Wall Grazing.

A regenerative cycle of tunsten and halogen atoms which prevent blackening of the lamp envelope during the life of the lamp.

Incandescent lamp with halogen gas fill and a quartz glass capsule. The quartz capsule requires a separate glass shield or enclosure. Due to the halogen cycle, halogen lamps operate at higher internal temperatures, producing more lumens per watt and brighter light than an ordinary incandescent; lamp life is also extended. Halogen lamps include A, MB, T, PAR and MR types.

Abbreviation for high intensity discharge. Generic term describing mercury vapour, metal halide, high pressure sodium, and (informally) low pressure sodium light sources and luminaires.

Fluorescent lamps designed to be used with an 800 milliampere ballast. Able to operate at low temperatures (down to zero) and still produce high light levels.

HPS lamps are high intensity discharge light sources which produce light by an electrical discharge through sodium vapour operating at relatively high pressures and temperatures.

These outdoor accent lights provide maximum concealment because the source is recessed into the ground. Both line and low voltage sources are available.

A lamp in which light is produced by a filament heated to incandescence by an electric current.

Luminaires that distribute all or most light upward to ambient (90 - 100 % of their light upward to be reflected by the ceiling).

Incandescent lamp with a light etching or sprayed-on diffusing coating on the inside of the bulb. Designated as IF.

Recessed down-lighting suitable for direct burial in ceiling thermal insulation. Called Type IC.

A heavy inert gas used in incandescent lamps that allows the filament to glow hotter and brighter and last longer.

This term describes the technical implementation of an artificial light source. The lamp is inserted into the lighting unit, which distributes and channels the light emitted by the lamp and protects against glare.

The peak lamp current divided by the RMS (average) lamp current. Lamp manufacturers require <1.7 for best lamp life. An LCCF of 1.414 is a perfect sine wave.

Socket inside a housing, which holds the lamp in place and connects it to the electrical source.

Fine quality glass having a high content of lead oxide.

Small pieces of glass joined at the edges with metal, traditionally lead.

Radiant energy that is capable of producing a visual sensation.

The distance from a reference point, usually the bottom of the lamp base, to the centre of the light source (filament).

Measured values of luminous intensity of point-like light source in all directions are applied to space from the light source as the radius-vectors. Linking these endpoints we get photometric luminance surface called light intensity distribution curve.

The performance of any light fixture depends on the light source, or bulb, that’s used. Different sources produce different effects.

Synonymous with lamp.

This term describes the strength of the illumination in a room or at specific places. It is also used when the light density is given as a lighting parameter instead of the lighting strength, this being the case for street lighting.

The entire body of the unit, including all components required for attachment, operation and protection, is described as a lighting unit.

Grid type of optical assembly used to control light distribution from a fixture. Can range from small-cell plastic to the large-cell anodised aluminium louvres used in parabolic fluorescent fixtures.

Low pressure sodium vapour lamps are mercury-free low pressure discharge lamps in which the sodium vapour discharge in the glass tube emits a monochromatic yellow light after ingnition.

A complete lighting unit including lamps, housing, lens and ballast if required. All the necessary components to make what we commonly refer to as a 'fixture'.

Glass shaped by mechanically forcing air into molten glass so that it takes the shape of a mould.

Lamp or fixture surface finish producing a diffuse, lightly textured dull reflection.

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum ( < Greek "hydr-" water and "argyros" silver). Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, mercury switches, and other devices though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out.It is used in lighting: electricity passed through mercury vapor in a phosphor tube produces short-wave ultraviolet light which then causes the phosphor to fluoresce, making visible light.

A high intensity discharge light source operating at a relatively high pressure (about 1 atmosphere) and temperature in which most of the light is produced by radiation from excited mercury vapour. Phosphor coating on some lamp types add additional light and improve colour rendering.

A high intensity light source in which the light is produced by the radiation from mercury, plus halides or metals such as sodium, scandium, indium and dysprosium. Some lamp types may also utilise phosphor coatings.

Base used on high-wattage incandescent and HID lamps.

Monochromatic is also called monochrome, means of a single colour. In monochromatic light, the light emission lies in a very narrow frequency of wavelength band.

The term mood lighting has established itself in LED lighting technology bacause it is possible to create moods using LEDs.

A low voltage quartz reflector lamp family of which the most popular is MR16. MR lamps surround a halogen capsule with a computer-designed glass, or metal reflector with many surfaces or facets. These compact lamps require a glass cover, either integral or with the fixture.

A reference direction directly below a luminaire, or 'straight down' (0 degree angle).

Full spectrum incandescent lamps. Also known as daylight or natural light. Uses a colored glass shell to filter out yellow light produced by standard incandescent lamps.

Low pressure arc discharge lamps that operate at high voltage. Used for decoration and signage purposes.

A system of dimming controls that are wired and programmed to respond together, usually to link controls in several rooms.

Abbreviation for National Institute of Standards and Technology.

Classic lighting is the popular paper lantern or shade style. Chinese and Japanese motifs may also be used to decorate table and floor lamps.

Lighting system that is used in an exterior space. Outdoor lighting can enhance the beauty of your home, making it safer and more secure.

PAR is an acronym for parabolic aluminised reflector. A PAR lamp that may utilise either an incandescent filament, a halogen filament tube or HID arc tube is a precision pressed-glass reflector lamp. PAR lamps rely on both the internal reflector and prisms in the lens for the control of the light beam.

A type of fluorescent fixture that has a louvre composed of aluminium baffles curved in a parabolic shape. The resultant light distribution produced by this shape provides reduced glare, better light control, and is considered to have greater aesthetic appeal.

Traffic lights using incandescent lamps have a reflector that bundles the emitted light. Under conditions where the sun presents an unfavourable angle of incidence, these refelctors give the impression that the corresponding lamp of the traffic lights is illuminated. This effect is called  a phantom light.

Refers to vision involving the cones of the eye; used in reference to the adaptation of the eye to illuminance of more than 3.4 candelas per square metre.

A compact fluorescent lamp with a double twin tube configuration

A gas filled tungsten incandescent lamp containing a proportion halogens in an insert gas whose pressure exceeds three atmospheres.

The point in hours where 50% of a lamp type initially started will still be functioning.

If the principle of thermal equilibrium is infringed in a physical system, there are processes that restore the ballance of the system. In semiconductors in contrast to metals, this takes place through so-called re-combination processes.

Upgrading a fixture, room or building by installing new lighting fixtures, parts or equipment.

On a ceiling fan, a switch that reverses the blade direction and airflow.

Scotopic vision is the vision of the eye under low light conditions. In the human eye cone cells are nonfunctional in low light – scotopic vision is produced exclusively through rod cells which are most sensitive to wavelengths of light around 498 nm (green-blue) and are insensitive to wavelengths longer than about 640 nm (red). See also Photopic Vision.

An illumination technology using phosphor-coated glass tubes filled with radioactive tritium gas. The exit sign uses no electricity and thus does not need to be hard-wired.

The angle measured from the ceiling plane to the line of sight where the bare lamp in a luminaire becomes visible. Higher shielding angles reduce direct glare. It is the complementary angle of the cut-off angle. (See also Cut-OFF Angle).

Accent lighting technique that creates a dramatic outline by back lighting. Also used in landscape lighting.

High Pressure Sodium abbreviation term.

Low Pressure Sodium abbreviation term.

A graph of the radiant power emitted by a light source as a function of wavelength. SPDs provide a visual profile of the colour characteristics of the light source throughtout the visible part of the spectrum.

Reflectorised lamp with a narrow light distribution.

Step Lights are recessed into walls and stairs so they illuminate the treads of stairs or pathways.

A solid angle sub-tending an area on the surface of a sphere equal to the square of the sphere radius.

Crystal of the ultimate chemical purity, saturated with more than 30% lead oxide, cut and polished with ultimate precision by a machine. This is the finest crystal available and also the most expensive.

Condition where rotating machinery or other rapidly moving objects appear to be standing still due to the alternating current supplied to light sources. Sometimes called 'strobe effect.'

The Toxicity Characteristic Leaching Procedure (TLCP) test, specified in the Resource Conservation and Recovery Act (RCRA) of 1990, is used to characterise fluorescent lamp waste as hazardous or non-hazardous waste. The TCLP test measures the ability of the mercury in a lamp to leach from a landfill into ground water under very aggressive and reactive conditions.

The upward inclination of a light source from a level horizontal position.

Tinted glass is clear glass with a pigment or colour added. This produces colour throughout the piece, which will not chip or peel. Also clear or opal glass with a thin film of coloured glass or plastic coating.

Indirect floor lamp that sends all, or most, of its light upward.

A long recessed lighting fixture, usually installed flush with the ceiling.

A gas filled tungsten incandescent lamp containing certain proportions of halogens in an inert gas.

Commonly refers to ceiling and wall fixture lighting that is plain and durable. Utility fixtures usually feature plastic lenses and diffusers instead of glass. The housing may also be of moulded plastic.

A fixture installed behind a horizontal shielding over a window or along a wall.

Fixture used at a mirror or over a vanity bathroom mirror. Ideally a long, well-diffused light source.

Abbreviation for visual comfort probability. A rating system for evaluating direct discomfort glare. This method is a subjective evaluation of visual comfort expressed as the percent of occupants of a space who will be bothered by direct glare. VCP allows for several factors: luminaire luminances at different angles of view, luminaire size, room size, luminaire mounting height, illuminance, and room surface reflectivity. VCP tables are often provided as part of photometric reports.

Fluorescent lamps designed to be used with a 1500 milliampere ballast.

A lighting technique in which light is aimed down a wall for a grazing effect. For dramatic shadows, especially on textured surfaces such as brick, draperies or stone.

Lighting directed on a wall or vertical surface to emphasise that plane, enhance the surface texture, or bounce light back into the room. Increasing wall brightness generally makes a room seem more spacious.

A lighting technique in which a wall is evenly washed with light.

A heavy, colourless, and relatively inert gaseous element that occurs in air as about one part in 20 million by volume and is used especially in thyratrons and specialised flashtubes.

The direction directly above the luminaire (180 degree angle).