Theme

Glossary

The following terms are used throughout our site or are predominant within the lighting industry.

2D Lamps
Compact fluorescent lamp with quadrant-like shape.
Absence Detection
A type of occupancy detection, requires user intervention before activation, turns off after delay period.
Acrylic
Polymethyl methacrylate, transparent plastic used in lenses.
Activiva Lamps
Special lamp with increased blue spectrum to increase well being.
Additive Colour Mixing
The use of different colours of light to produce another colour, as used with LED RGB systems.
Anti Ligature
A luminaire with no ligature points suitable for use in specialist hospital and custodial environments.
Anti Vacuum Breathing Device
A device on high power discharge floodlights to reduce condensation due to the pressure differences when switched and off.
Asymmetric
This relates to the distribution of light from a luminaire. The distribution is biased to one direction. In relation to floodlights, they can be kept at a low til angle and still throw light to where it is required, this helps reduce sky glow.
Ballast Lumen Factor (BLF)
The ratio of the light output of the lamp when the ballast under test is operated at its design voltage, compared with the light output of the same lamp operated with the appropriate reference ballast supplied as its rated voltage and frequency
Cat 1 Louvre
A louvre that usually has a luminance limit of 200cd/m2 at an elevation of 55°. These were withdrawn in the Lighting Guide 3: Addendum 2001.
Cat 2 Louvre
A louvre that usually has a luminance limit of 200cd/m2 at an elevation of 65°. These were withdrawn in the Lighting Guide 3: Addendum 2001.
Central Battery System
A emergency lighting system in which the batteries for a number of luminaires are housed in one location, usually for all the emergency luminaires in one lighting sub-circuit, sometimes for all emergency luminaires in a complete building.
Ceramic Lamps
A type of high intensity discharge metal halide lamp with a compact ceramic arc tube.
Colour Rendering
A general expression for the appearance of surface colours when illuminated by light from a given source compared with their appearance under light from a reference source.
Colour Temperature (K)
The temperature of a 'full radiator' which emits radiation of the same chromaticity as the radiator being considered.
Constant Current
A term used to describe a system that can vary the voltage across an electric circuit to maintain a constant electric current, as used with high power LEDs.
Contrast
Describes the difference in appearance of two parts of a visual field seen simultaneously or successively.
Cross Ward Glare
In multi bedded hospital wards, discomfort glare caused by luminaires used by patients and or nursing staff on the opposite side of the ward.
Cut-off Angle
The angle above which no reflection of the light source is visible in the reflector.
Diffuse Reflection
Reflection in which the reflected light is diffused and there is no significant specular reflection, as from matt paint.
Digital Addressable Lighting Interface (DALI)
Digital control protocol used in lighting systems. The protocol allows luminaires to be controlled individually by addressing individual units.
Digital Multiplex (DMX)
This digital control protocol is primarily used for lighting control in the entertainment market but can be used to control specific LED drivers.
Digital Serial Interface (DSI)
Digital control protocol created by Tridonic Atco used for controlling lighting. Luminaires can not be addressed as with a DALI system.
Direct / Indirect
A type of lighting system that combines both downward lighting and upward lighting components.
Disability Glare
Glare produced directly or by reflection that impairs the vision of objects without necessarily causing discomfort.
Discomfort Glare
Glare which causes discomfort, for example the sensation caused by viewing a snowfield under bright sunlight.
Downlighter
Direct lighting luminaire from which light is emitted only within relatively small angles to the downward vertical.
Downward Light Output Ratio (DLOR)
The ratio of the total light output of a luminaire below the horizontal under stated practical conditions to that of the lamps or lamps under reference conditions.
EULUMDAT (LDT)
Internationally recognised photometric file format containing intensity data measured under reference conditions.
Fluorescent Lamp
A gas discharge lamp that uses electricity to excite mercury vapour. The excited mercury atoms produce short-wave ultraviolet light that cause a phosphor to fluoresce, producing visible light.
Glare
The discomfort or impairment of vision experienced when part of the visual field are excessively bright in relation to the general surroundings.
High Frequency
A type of electronic control gear that uses high frequency current to run fluorescent lamps. The frequencies used are approximately 30kHz to 40kHz.
HPI Lamps
Metal Halide lamp that uses a quartz arc tube.
Ignitor
Piece of control gear that causes the ignition of discharge lamps by creating voltage peaks.
Illuminance
The luminous flux density at a surface, i.e. the luminous flux incident per unit area.
Induction Lamps
A lamp that uses a high frequency generator and a ferrite core to induce current in a fluorescent chamber. Operating frequency depends on manufacturer, Philips uses 2.65MHz, Osram uses 250 kHz.
Infrared (IR)
Invisible radiation longer than that of visible light.
Inverse Square Law
Describes the reduction of illuminance at a point proportional to the square of the distance from the light source.
Ingress Protection (IP)
The Ingress Protection or IP rating classifies the degree of protection from dust and moisture. This system is recognised by most European countries.
Lamp Lumen Maintenance Factor (LLMF)
The proportion of the initial light output of a lamp that is produced after a stated period of operation.
Lamp Survival Factor (LSF)
The percentage of functioning lamps in an installation after a stated period of operation.
LED Lamps
Light Emitting Diode. Electro-luminescence emitter which generates light through recombination of charge carrier pairs in a semi-conductor.
LG2
Society of Light and Lighting, Lighting Guide 2: Hospital and health care buildings.
LG4
Society of Light and Lighting, Lighting Guide 4: Sports
LG5
Society of Light and Lighting, Lighting Guide 5: Lecture, teaching and conference rooms.
LG6
Society of Light and Lighting, Lighting Guide 6: The outdoor environment.
LG7
Society of Light and Lighting, Lighting Guide 7: Office lighting
LG10
Society of Light and Lighting, Lighting Guide 10: Daylight and window design.
LG11
Society of Light and Lighting, Lighting Guide 11: Surface reflectance and colour.
LG12
Society of Light and Lighting, Lighting Guide 12: Emergency lighting design guide.
Light Output Ratio (LOR)
The ratio of the total light output of a luminaire under stated practical conditions to that of the lamp or lamps under reference conditions.
Lumen (lm)
The SI unit of luminous flux, used in describing a quantity of light emitted by a source or received by a surface.
Luminaire Maintenance Factor (LMF)
The proportion of the initial light output from the luminaire that occurs after a set period of time due to dirt deposition on and in the luminaire.
Luminance (cd/m2)
The physical measure of the stimulus which produces the sensation of brightness measured by luminous intensity of the light emitted or reflected in a given direction from a surface element, divided by the projected area of the element in the same direction.
Luminous Efficacy (lm/w)
The ratio of the luminous flux emitted by a lamp to the power consumed by the lamp.
Luminous Flux (lm)
The light emitted by a source, or received by a surface.
Luminous Intensity (cd)
A quantity which describes the power of a source or illuminated surface to emit light in a given direction.
Lux
The SI unit of illuminance, equal to one lumen per square metre.
Magnetic
Control gear for SON and Metal Halide lamps, uses a copper and iron to regulate the current being supplied to the lamp.
Maintained Emergency
A luminaire containing one or more lamps, all of which operate from the normal supply or from the emergency supply at all material times.
Maintenance Factor (MF)
The ratio of the illuminance provided by an installation at some stated time, with respect to the initial illuminance.
MHN Lamps
Metal Halide lamp that uses a compact quartz arc tube.
Mixed Reflection
Partly specular and partly diffused reflection, as from smooth, glossy paint.
Mounting Height
Usually the vertical distance between a luminaire and the working plane, In some cases the floor may be the effective working plane.
Multi Wattage Control Gear
Electronic control gear for fluorescent lamps that has an output capable of driving lamps of different wattages from the same piece of control gear.
Nickel Cadmium Battery (NiCad)
Battery used in emergency lighting products.
Nickel Metal Hydride Battery (NIMH)
Battery used in emergency lighting products, require special charge circuits to ensure optimum battery life.
Night Light
In hospitals and health care buildings, the lighting at night needs to achieve two things, first to provide enough light for the safe movement around the ward area and, secondly, to allow the nursing staff the ability to discern facial features and a patients general condition.
Non maintained Emergency
A luminaire containing one or more lamps which operate from the emergency supply only upon failure of the normal mains supply.
Optiview Lamps
Linear fluorescent lamps dedicated to the health care market giving an increase in light above 600nm.
Patient Reading Light
As used in hospital wards. Patient controlled light to allow for the user to be able to perform local tasks, care should be used to avoid cross ward glare.
PIR
Passive infra-red. A method of detection used in presence detection systems. Measure heat movement against the back ground heat.
PLC Lamps
Compact long arc low pressure mercury discharge lamp. Envelope consists of four parallel narrow fluorescent tubes.
PLL Lamps
Compact long arc low pressure mercury discharge lamp. Envelope consists of two parallel narrow fluorescent tubes linked by a bridge.
PLR Lamps
Compact long arc low pressure mercury discharge lamp. Envelope consists of six parallel narrow fluorescent tubes.
PLS Lamps
Compact long arc low pressure mercury discharge lamp. Envelope consists of two parallel narrow fluorescent tubes.
PLT Lamps
Compact long arc low pressure mercury discharge lamp. Envelope consists of six parallel narrow fluorescent tubes.
Polar Lamps
Fluorescent lamps which perform better at a lower temperature than standard fluorescent lamps.
Power Factor
In an electric circuit the power factor is equal to the ratio of the root mean square power in watts to the product of the root mean square values of the voltage and current; for sinusoidal waveforms the power factor is also equal to the cosine of the angle of phase difference between voltage and current.
Presence Detection
A type of occupancy detection. Turns on as soon as occupancy has been detected and turns off after a delay period after the last occupancy has been detected.
Reflectance
The ratio of the luminous flux reflected from a surface to the luminous flux incident on it. Except for matt surfaces, reflectance depends on how the surface is illuminated but especially on the direction of the incident light and its spectral distribution.
Room Index (K)
An index related to the dimensions of a room and used when calculating the utilisation factor and other characteristics of the lighting installation.
Room Surface Maintenance Factor (RSMF)
The proportion of the illuminance provided by a lighting installation in a room after a set period of time compared with that when the room was clean.
Secura Lamps
Fluorescent lamps with a protective coating around the lamp to prevent lamp contamination resulting from breakage.
SON Lamps
High pressure Sodium lamps.
Spacing to Height Ratio (SHR)
The ratio describes the distance between the luminaire centres in relation to their height above the working plane. For a regular square arrangement, it is the distance between adjacent luminaires divided by their height above the working plane.
Spacing to Height Ratio Maximum (SHR MAX)
The SHR for a four by four square array of luminaires that gives a ratio of minimum to maximum direct illuminance of 0.7 over the central region between the four innermost luminaires.
Spacing to Height Ratio Maximum Transverse (SHR MAX TRANS)
The SHR in the transverse plane for continuous lines of luminaires that gives a ratio of minimum to maximum direct illuminance of 0.7 over the central region between the two inner rows.
Spacing to Height Ratio Nominal (SHR NOM)
The highest value of SHR in the series 0.5, 0.75, 1.0 etc., that is not greater than SHR MAX.
Specular Reflection
Reflection without diffusion in accordance with the laws of optical reflection as in a mirror.
Subtractive Colour Mixing
The process of changing the colour of a light source by placing coloured filters between the source and the viewer in order to subtract the wavelength of the filter from original source of light.
Sustained Emergency
An emergency luminaire that contains two or more lamps as least one of which is energised from the emergency supply and the remainder from the normal supply. The lamp energised from the the emergency supply in a combined emergency luminaire is either maintained or non-maintained.
Switch Start
A control gear arrangement for fluorescent lamps, uses a choke to limit the current flow through the lamp and a starter to produce a high voltage pulse to initiate the arc.
Symmetric
Relates to the distribution of light from a luminaire. The distribution is the same on opposing axes
T12 Lamps
Linear fluorescent lamps having a diameter of 12 1/8ths on an inch (1 1/2 inch). These are due to be phased out in the governments ban the bulb campaign.
T5 Lamps
Linear fluorescent lamps with a diameter of 5 1/8ths of an inch (approximately 16mm). All T5 lamps are triphosphor.
T8 Lamps
Linear fluorescent lamps with a diameter of 8 1/8ths of an inch (1 inch). T8 lamps can be either Halophosphate or triphosphor, halophosphate variants are due to be phased out in line with governments ban the bulb campaign.
TCP/IP
The Internet Protocol Suite (commonly known as TCP/IP) is the set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP). In lighting it is starting to be used in control systems to allow wide area communications.
T Grid
A type of ceiling system that uses an inverted T section on which sits ceiling tiles. The size of the T bar can be either 24mm or 15mm. The ceiling tiles can be replaced by a luminaire that sits on the T bar.
TP(a) Flexible
Thermoplastic material used in diffusers. The material must not be more than 1mm thick and comply with the type C requirements of BS 5438, test 2, 1989.
TP(a) Rigid
Thermoplastic material used in diffusers and can be made from PVCu or Polycarbonate. Diffusers made from polycarbonate at least 3mm thick achieving Class 1 rating when tested to BS 476 pt 7.
TP(b)
Thermoplastic material used in lighting diffusers. Diffusers these are usually styrene, acrylic or polycarbonate less than 3mm thick.
Ultraviolet (UV)
Invisible radiation beyond short-wave light (<380nm wavelength). Technical light sources only emit a limited amount of (UV) radiation.
Uniformity
The ratio of the minimum illuminance (or luminance) to the average illuminance (or luminance) over a specified surface. The ratio usually applies to values on the task area over the working plane.
Upward Light Output Ratio (ULOR)
The ratio of the total light output of a luminaire above the horizontal under stated practical conditions to that of the lamp or lamps under reference conditions.
Uplighting
A method of lighting a space by bouncing the light off the ceiling before it illuminates the task area. This produces an aesthetically pleasing environment.
Utilisation Factor (UF)
The proportion of the luminaires flux emitted by the lamps which reaches the working plane.
Voltage (V)
Physical quantity which sets charge carriers in an electrical conductor in motion to produce an electric current.
Watch Lighting
In health care wards, localised lighting at the bedhead to allow staff to continuously monitor and observe patient's progress during critical period such as post-operative care or during critical illness.
Watt (W)
The watt is a derived unit of power in the international system of units (SI). It measures rate of energy conversion. One watt is equivalent to 1 Joule of energy per second.
Wavelength (NM)
The wavelength of a sinusoidal wave is the spatial period of the wave - the distance over which the wave's shape repeats.
Working Plane
The horizontal, vertical or inclined plane in which the visual task lies. If no information is available, the working plane may be considered to be in the horizontal plane at 0.8 m above the floor.
Xtra Lamps
Long life lamps that can be used on high frequency control gear.
Xtreme Lamps
Linear fluorescent long life lamps that are recommended to run on dedicated high frequency control gear.