Common Lighting Terms & Definitions
12/12 – Light being turned “On” for 12 hours per day and “Off” for 12 hours per day.
18/6 – Light being turned “On” for 18 hours per day and “Off” for 6 hours per day.
ALTERNATING CURRENT (AC) – An electric current reversing its direction regularly at certain intervals.
AMBIENT LIGHTING – Also can be referred to as general lighting. This is the all around, uniform illumination that lights up every home.
AMP – Watts Divided by Volts. The unit used to measure electric current. The amount of current sent through one ohm by one volt.
ANSI – American National Standards Institute. The organization that develops voluntary guidelines and produces performance standards for the electrical and other industries.
AVERAGE RATED LIFE – An average rating in hours that indicates when 50% of a large group of lamps have failed when operated at nominal lamp voltage and current.
AUTO-SENSING VOLTAGE – typically referring to a driver in the lighting markets. Quality drivers typically have a circuit which auto selects the input voltage and rectifies it to a DC voltage for use by the LEDs. Typical ranges are 90 thru 308 volts. This feature makes applying the wrong voltage and blowing the luminaire less likely.
BALLAST – A device that provides the necessary starting voltage and appropriate current to a fluorescent or high intensity discharge (HID) luminaire.
BALLAST FACTOR – A ratio used to calculate the expected real-world performance of a lamp. Calculated as the difference between the expected performance of a lamp with a commercial ballast versus the measured performance of that lamp with a reference ballast. Rated Lamp Lumens x Ballast Factor = Net Lumens.
BASE – That part of the light bulb which is placed inside the socket (Usually, these are screw-in and made of either aluminum or brass). For HID bulbs they might be ceramic. For compact fluorescent, they mostly have either two or four pins. The two-pin versions are designed for preheat and have an internal starter. The four pin types (which are dimmable) do not have an internal starter and it needs a ballast to be operated. Slimline fluorescents have only one pin at either end of the lamp. (See also Fluorescent and HID).
BTU – The British thermal unit is a traditional unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is part of the British Imperial system of units. Its counterpart in the metric system is the calorie, which is defined as the amount of heat required to raise the temperature of one gram of water by one degree Celsius. Heat is now known to be equivalent to energy, for which the metric unit is the joule; one BTU is about 1055 joules. While units of heat are often replaced by energy units in scientific work, they are still important in many fields.
COB – COB (Chips on Board) is a new technology of LED packaging for LED light engine. Multi LED chips are packaged together as one lighting module. When it’s lit up, it looks like a lighting panel.
CRI – Color Rendering Index. The ability of a light source to accurately render an object’s color in comparison with a natural light source. Measured on a scale of 1 -100 with 100 being the ideal. The CRI runs from 1 (for Low Pressure Sodium lamps) to 100 (for the Sun). A CRI somewhere in the 80’s will give you good and true color portrayal.
COLOR TEMPERATURE – A numerical scale used to describe the color of light. Light with a lower Kelvin rating will have a more yellow hue, while light with a higher kelvin rating will have a more blue tint. Also known as Kelvin Temperature.
COMPACT FLUORESCENT LAMP (CFL) – These are small long living fluorescent lights that can be used as an alternative to incandescent bulbs.
cUL – (Canadian Underwriters Laboratory) – A wholly independent organization that apply strict tests to electrical manufacturer’s products. When and if they pass these tests, the makers can designate them as ‘cUL Listed’. Numerous insurance companies want to see these labels to ensure manufacturers adhere to these standards to minimize the public’s risk.
DAMP LOCATION – A UL listing (see UL) for fixtures that are used in locations where there is moisture present.
DAYLIGHT SENSOR – A device which senses the amount of daylight in a room and controls the luminaire accordingly.
DIRECT – A direct source of light which is cast downwards from a fixture to provide lighting with uniform levels of illumination. Open, louvered, and lensed fixtures can all be “direct”. Also see Indirect and Direct/Indirect.
DID (Direct/Indirect) – A source of light in which light is cast both upwards and downwards from a fixture to provide a combination of direct and indirect illumination.
DIMMER – A control switch that reduces the illumination of a lamp by lessening the electricity available to it. These may be incremental, or full range with rotary or slide controls.
DIRECT CURRENT (DC) – An electric current that flows continuously in only one direction without any alterations.
DESIGN LIGHTING CONSORTIUM – The DLC® is a non-profit organization whose mission is to drive efficient lighting by defining quality, facilitating thought leadership, and delivering tools and resources to the lighting market through open dialogue and collaboration. Having lights listed on this site shows the real, honest lumen output, electrical load. Most utility companies use this site to verify that LED lights qualify for municipality rebates.
DOWNLIGHTING – Light which is cast downward from a fixture. This is the most common and direct form of lighting.
DRIVER – s an electrical circuit used to power a light-emitting diode (LED). The circuit must provide sufficient electrical current to light the LED at the required brightness, but must limit the electrical current to prevent damaging the LED. The voltage drop across an LED is approximately constant over a wide range of operating electrical current; therefore, a small increase in applied voltage greatly increases the current. Very simple circuits are used for low-power indicator LEDs. More complex, current source circuits are required when driving high-power LEDs for illumination to achieve correct current regulation.
EFFICACY – A measure expressed in lumens per watt representing the efficiency of a lamp/ballast system or luminaire. A guide to the efficiency of a light bulb expressed in lumens per watt (LPW). The higher the number, the more light given out for energy used.
ECM – Energy Conservation Measures. A term commonly used by ESCOs in lighting audits/designs.
ESCO – Energy Service Company. A company dedicated to helping commercial and industrial clients reduce their energy consumption.
EXTENDED LIFE LAMP – Light bulb with an average rated life of 2500+ hours.
FC-FOOT-CANDLE. A unit of measure for the density of light as it reaches a surface. One foot-candle is equal to 1 lumen per square foot.
FLUORESCENT – A lighting system which works by creating electric arcs inside a gas rich tube to produce ultraviolet light, then converting this to visible light by its passage through a layer of phosphor on the inside of the glass tube. Contains mercury and requires proper disposal (not a trash can).
FULL SPECTRUM – Light bulbs with this designation accurately imitate natural light and are thought by some to be beneficial to health by reducing stress, depression and headaches, amongst other things.
HALOGEN LAMP – A type of bulb which contains halogen gases, usually iodine, or chlorine, bromine, or fluorine, to extend the life of the tungsten filament through a recycling system known as the halogen cycle. They are also made of quartz glass, or ‘hard glass’ because they have to be hotter to work properly. Halogen bulbs are brighter and produce more lumens per watt (LPW).
HEAT SIGNTUARE – The apparent temperature difference method of defining infrared signature gives the physical temperature difference (e.g. in kelvins) between the object of interest and the immediate background if the recorded radiance values had been measured from perfect blackbody sources. Problems with this method include differences in radiance across the object or the immediate background and the finite size of the detector’s pixels. The value is a complex function of range, time, aspect, etc.
HEAT SINK – A component or integral part of a luminaire that conducts or convects heat away from LED components.
HI-BAY – Lighting used in industrial applications where the ceiling height is greater than 20 feet. Common in big box retail, industrial, warehouse and manufacturing spaces.
HID – High Intensity Discharge lamps. A group of type of lamps that include mercury vapor, high pressure sodium, low pressure sodium and metal halide. They are long lasting and energy efficient.
HPS – High Pressure Sodium HID Lighting.
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 1lux.
INCANDESCENCE – Light produced by the electrical heating of a material.
INDIRECT – An indirect source of light which is cast upwards from a fixture and bounced down to provide lighting with minimal glare and more uniform levels of illumination.
INITIAL LUMENS – The lumens produced by a lamp after an initial burn in period (usually 100 hours).
INPUT WATTS – The total wattage required by both the ballast and the lamp in a luminaire.
INSTANT START – Ballast starting type. Applies high voltage across the lamp with no preheating of the cathode.
IP RATING – The IP Code, International Protection Marking, IEC standard 60529, sometimes interpreted as Ingress Protection Marking, classifies and rates the degree of protection provided against intrusion (body parts such as hands and fingers), dust, accidental contact, and water by mechanical casings and electrical enclosures. Examples are below.
IP51 – Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment. Dripping water (vertically falling drops) shall have no harmful effect on the specimen when mounted in an upright position onto a turntable and rotated at 1 RPM.
IP56 – Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment. Protection against Water projected in powerful jets (12.5 mm nozzle) against the enclosure from any direction shall have no harmful effects.
JUNCTION – The p-n junction in a diode, an LED for instance, where positively charged and negatively charged materials exchange electrons, emitting photons and generating heat.
JUNCTION TEMPERATURE – The temperature in the vicinity of an LED’s p-n junction. Controlling junction temperature is critical for achieving the optimal balance between lumen output and lumen maintenance.
KELVIN TEMPERATURE – A numerical scale used to describe the color of light. Light with a lower Kelvin rating will have a more yellow tint, while light with a higher kelvin rating will have a more blue tint.
KILOWATT -1000 Watts.
KILOWATT HOUR – 1000 Watts used continuously for one hour.
LAMP – The source of light in a fixture, typically called a “light bulb.”
LAMP DISPOSAL – Refers to the proper recycling of lamps containing mercury (like fluorescent bulbs) or other hazardous materials.
LED – Light Emitting Diode – LED is a semiconductor devise that emits visible light of a certain color.
LED DRIVER – An electronic device which converts input power into a constant current source despite fluctuation in voltage. It protects LEDs from voltage fluctuations. In simple terms, an electronic device which feeds input power to the LED to produce light.
LLD – Lamp Lumen Depreciation Factor. 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 relamping program to be used. (See also Lumen Depreciation and Mean Lumens).
LENS – A glass or plastic element used in luminaries to seal a fixture or control the exiting light.
LLF – Light Loss Factor. 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, etc.
LO-BAY – Lighting used in industrial applications where the ceiling height is 20 feet or less. Common in big box retail and industrial settings.
LOW VOLTAGE – Lamps that use 6, 12, or 24 volts instead of 120, and require a transformer connected between them and the standard 120 volt power source.
LM-79 – The approved method by IES for making photometric measurement of LED light products. LM-79 measures total luminous flux, luminous intensity distribution, electrical power, efficacy and color characteristics (chromaticity, CCT, and CRI).
LM-80 – A measurement standard developed by IES which allows user to evaluate and compare the lumen maintenance of LED components from different manufacturer at standard operating condition. LED packages, arrays or LED modules can be tested at three junction temperatures typically at 55°C, 85°C & a manufacturer specified temperature for 6000 hours. The approved method of measuring lumen maintenance is only for LED light source not complete luminaire.
LPW – Lumens Per Watt. The number of lumens produced by a light source for each watt of electrical power supplied to the light source. This is used to measure the overall efficacy of a luminaire.
LUMEN DEPRECIATION – The decrease in lumen output of a light source over time; every lamp type has a unique lumen depreciation curve (sometimes called a lumen maintenance curve) depicting the pattern of decreasing light output.
LUMEN MAINTENANCE – Lumen maintenance is the standard lighting term for the percentage of initial lumens that a light source maintains over time. For instance, P-2’s QHC maintains 70% of initial lumens over 60,000 hours and specified as L70 over 60,000 hours (or 30% of deterioration in the amount of light produce by QHC over a period of 60,000 hours). Lumen maintenance is often specified as L50, L70, L80, or L90. In each case, L stands for lumen maintenance and the number is the percentage of light output remaining.
LUMENS – A unit of luminous flux; overall light output; quantity of light, expressed in lumens.
LUMINAIRE – A complete lighting unit which contains a lamp, housing, ballast, sockets and any other necessary components.
LUMINAIRE EFFICIENCY – The ratio of lumens emitted by a luminaire to the total lumens emitted from the light source within the luminaire.
LUX – A unit of illuminance equal to 1 lumen per square meter.
MEAN LUMENS – The average lumen output of a lamp over its rated life. Mean lumen values for fluorescent and HID lamps are typically measured at 40% of their rated lives.
MH – Metal Halide (HID) lighting.
MULTI-VOTAGE – The ability for an electrical device to operate on more than one source voltage. This is optional on some LEDs and allows the item to run for example on 120, 230 or 277 VAC, single phase.
NEMA (National Electrical Manufacturers Association) – An organization for promoting harmony and agreement within the industry, and deciding on the designation of new products.
PAR (PHOTOSYNTHETICALLY ACTIVE RADIATION) – Designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis. This spectral region corresponds more or less with the range of light visible to the human eye. PPF and YPF sensors were the least accurate for narrow-band sources (narrow spectrum of light) and most accurate broad-band sources (fuller spectra of light). They found that PPF sensors were significantly more accurate under metal halide, low-pressure sodium and high pressure sodium lamps than YPF sensors (>9% difference). NOTE: Both YPF and PPF sensors were very inaccurate (>18% error) when used to measure light from red-lightemitting diodes, such as red LED chip(s) in an LED light.
PHOTOPIC LUMENS – A type of light measured in lumens. It is generally detected by common light meters and accounts for part of the human eye’s perception of brightness.
POWDER COATING – a type of coating that is applied as a free-flowing, dry powder. The main difference between a conventional liquid paint and a powder coating is that the powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form. The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a “skin”. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional liquid paint. Powder coating is mainly used for coating of metals. This is environmentally greener and maintains a tougher finish.
POWER FACTOR – A measure of the effectiveness with which an electrical device converts volt-amperes to watts;devices with power factors (< 0.90) are “high power factor” devices.
RAPID START – A method of starting typically associated with magnetic ballasts; where a low filament voltage is applied to preheat the cathodes.
RE-STRIKE – Refers to the restarting of a previously operating lamp shortly after turnoff. Metal halide lamps typically require a minimum of 4-15 minutes to restart after turn-off.
REFLECTOR – A device for reflecting light in a chosen direction from its surface. Depending on the brightness desired, they may be either diffuse, glossy, matte, or specular. (See Diffused Lighting, Gloss, Matte and Specular).
RLO – Relative Light Output. The ratio of light output between a fixture’s potential light output at optimum ambient temperatures and actual light output at actual ambient temperatures. For example, if a fixture at its optimal temperature of 75°F produces 10,000 Lumens and 8,000 Lumens 50°F, that fixture’s RLO at 50°F is 8,000 Lumens ÷ 10,000 Lumens, or 80%.
SOLID-STATE LIGHTING – A description of the devices that do not contain moving parts or parts that can break, rupture, shatter, leak or contaminate the environment.
S/P RATIO – The ratio of scotopic to photopic lumens produced by a light source. An appropriate S/P ratio will provide for a more comfortable atmosphere and better perceived brightness.
SPD (Spectral Power Distribution) – An illustration of how the power output of a given bulb changes in each different wavelength across the spectrum.
SPECULAR – A highly polished or mirrored surface.
T5 – 5/8″ diameter fluorescent lamps. “T” stands for tubular, while the number “5” stands for the 5 in 5/8”. Therefore a T8 lamp would be a Tubular 8/8”, or 1” diameter lamp.
T8 – 1″ diameter fluorescent lamps.
T12 – 1 1/2″ diameter fluorescent lamps.
THERMAL CHARACTERISTICS – The manner in which a luminaire manages heat, either dissipating heat or retaining it.
THERMAL ANALYSIS – Thermal analysis is a branch of materials science where the properties of materials are studied as they change with temperature. In LED lighting, this analysis is important to know how long the light will last in a given ambient temperature and the percentage output that it is run at.
THD – Total Harmonic Distortion. A measure of the distortion of an electrical wave form. Excessive THD (defined by ANSI as greater than 32%) may cause adverse effects to the electrical system.
UL (Underwriters Laboratory) – A wholly independent organization that apply strict tests to electrical manufacturer’s products. When and if the products pass these tests, the manufacturer can designate them as ‘UL Listed’. Insurance companies want to see these labels to ensure manufacturers adhere to these standards to minimize risk. Many insurance companies do not cover losses from non-UL rated electrical devices such as lighting fixtures.
UPLIGHTING – A source of light which is cast upwards to illuminate a ceiling cavity for aesthetic reasons. When combined with reflective ceiling materials, uplighting can function as a source of indirect lighting.
VOLTS – The unit of electrical force or pressure that creates current.
WIRELESS CONTROL – the ability to control the light via remote control without a wire. “On” or “Off” is one of the functions on the controller, 0-100% intensity of light output is another function.