Glossary of Lighting Terms

  • Ambient Temperature-Describes the temperature of the air around a light fitting. The performance of an LED light is affected more by ambient temperatures than other forms of light. Heat-sinking helps maintain the lifespan of LED lights.

    ANSI-American National Standards Institute.

    Amperes or Amps-Measure of electrical current flow in a circuit.  Amps are considered when sizing electrical wiring.

    Ballast-A device used to manage the power to fluorescent or HID lamps. It controls the steady state power to a lamp, and may provide the means for these light sources to start.

    Ballast factor-Ballast factor (BF) is a scalar term that defines the power consumed and light output from a ballast.  Electronic T8 ballast comes in four common values: Low (L, 0.77), Normal (N, 0.88), Normal+ (N+, 1.00), or high (H, 1.18).  For example, a Normal ballast factor powering an ANSI stardard 32W T8 lamp will produce full light from the lamp, but consume only .88 the power (28W).  A Low ballast factor will produce 12% less light and consume 12% less power than Normal ballast factor ballast.

    Beam Angle-As defined by IES LM-79, the beam angle is the angle at which light decreases to 50% of its maximum, with the maximum typically occurring at nadir (center-down).  Beam angle may be defined along two axis of the light source.  A standard TLED has a beam angle of around 120 degrees.  Beam angle should not be confused with Beam Angle Aperture.

    Bulb Base-Used to secure a bulb in place and connect it to a source of electricity. There are many types and sizes. Different types of light bulbs are often identified by their base. These are normally either a screw or bayonet. For example: E26 is the most common “Edison” screw base for bulbs.  GU10 have a standard 2-pin fitting, G24 bases are common in un-ballasted fluorescent bulbs.

    Burn hours-The time in hours that the tube is on or burning.

    CFL-Compact Fluorescent Lamp. A small fluorescent light, used as a more efficient alternative to incandescent lighting.

    CCT-Correlated Color Temperature.  For predominantly white light sources, CCT is the temperature of a blackbody with equivalent color cast, as defined by ANSI 78.377. .   Color temperature describes whether a light source appears ‘warm’ or ‘cool’ – indicated by the CCT. Lamps with a warm appearance have a CCT of 2700-3500K, and are considered appropriate for domestic settings; cooler lamps might be 4000K, and are used more often in offices and retail. The higher the color temperature, the ‘cooler’ the appearance.  5000K are generally used in industrial high bay applications.  The Sun has a CCT of 5700.

    CRI-Color Rendering Index. A quantitative measure of the ability of a light source to accurately reproduce colors, as compared with an ideal or natural light source. Light sources with a high CRI are desirable in color-critical applications. Higher CRI allows the eye to see with better definition. The maximum level of CRI is 100.

  • Dali-The Digital Addressable Lighting Interface is a protocol for lighting controls and dimming agreed by major manufacturers. Originally developed by Philips, it is now an open technical standard, IEC 62386.

    Diffuser-A diffuser is applied to a light source to spread light more evenly. It is made of translucent glass or plastic, and gives a much softer light. This is useful for general lighting, where the light needs to be less directed.

    Direct fit-A plug-and-play, or ballast-compatible, linear LED one-for-one swap out of the original linear fluorescent lamp. This lamp works directly with the existing fluorescent ballast, so there is no rewiring nor ballast change required.  Being a ballast compatible lamp, the ballast efficiency (ballast factor) is crucial for the lamp’s true energy efficiency.  Safety standard: UL type A.

    Direct wire-Also known as line voltage or ballast-bypass linear LED retrofit, works straight off the line voltage flowing directly to the sockets, bypassing the incumbent fluorescent ballast.  A direct wire lamp is powered by the most efficient internal driver designed specifically for the TLED system.  Ballast factor loss is not a concern in direct wire retrofit.  Safety standard: UL type B.

    Directional Light Source-Describes a light source which points light in a specific direction. This is useful for providing extra light to a task, or for decorative or highlighting purposes. LEDs provide a good directional light source.

    DLC QPL-DesignLights™ Consortium Quality Products List. The list provides the necessary information for energy efficiency program administrators to use internally to determine whether the LED fixture qualifies for possible incentives. It identifies a qualified fixture and lists its attributes including:
    • Manufacturer
    • Brand
    • Model
    • Product Type
    • Luminaire Efficacy
    • Light Output
    • Rated Lifetime
    • Power Factor
    • Color Temperature
    • Date Qualified
    • Others

    DOE-The United States Department of Energy.

    Efficacy-Ratio of the amount of light produced by a lamp to the power required to produced it. Measured in lumens per watt (lm/W).

    EIA-The United States Energy Information Administration.

    EISA-Energy Independence and Security Act of 2007.

    Flicker-Flicker is a generic term for temporal light modulation, or a change in brightness over time.  Flicker is associated with photosensitive epilepsy, and is known to cause headaches, irritability, eye strain.

    Flicker-free-Although there is no industry standard for flicker-free definition, since the publication of IEEE 1789-2015, it is commonly accepted that <5% flicker is flicker free.  At Energy Focus, there are products certified by UL (with UL Verified Mark) to be as low as <1% flicker.

    Flicker percentage-Flicker percentage, or percent flicker, is an IES measurement method to characterize amount of flicker in output of a light source.  The lower the percent flicker the higher quality of light. This could result in health and wellness benefit for the users.

    Foot-candle-A non-standard measurement of illuminance or light intensity.  A unit of illumination (now little used) equal to that given by a source of one candela at a distance of one foot (equivalent to one lumen per square foot or 10.764 lux).

    Fluorescent-A type of light sources based on exciting a mercury plasma, typically in a glass tube. Fluorescent lights contain mercury gases which are released if the lamp is broken. Mercury gas can be dangerous, so LEDs provide a safer and more environmentally friendly option.

    GaN-Gallium Nitride, the semiconductor most prevalent in the fabrication of the LED chips used in white LEDs.

    Haitz's Law-Haitz's law is an observation and forecast about the steady improvement, over many years, of light-emitting diodes (LED). It states that every decade, the cost per lumen (unit of useful light emitted) falls by a factor of 10, and the amount of light generated per LED package increases by a factor of 20, for a given wavelength (color) of light.

    Halogen lamp-Also known as a tungsten halogen, quartz-halogen or quartz iodine lamp, is an incandescent lamp consisting of a tungsten filament sealed into a compact transparent envelope that is filled with a mixture of an inert gas and a small amount of a halogen such as iodine or bromine.

    Heat Sink-A heat sink is used to take heat away from certain parts of an electronic circuit. Because LEDs are sensitive to heat, a heat sink is often an important part of an LED luminaire. Heat sinks help to preserve the lifespan of LED lights.

    HID-HID stands for High Intensity Discharge. It describes a kind of light source used in warehouses (high bays), football stadiums, and large public areas. They are typically very bright and are also energy efficient. They are often used as car headlights.

    HPS-High Pressure Sodium. A traditional lighting method for outdoor lighting, recognizable by a heavy orange glow.

    HO-High output lamps. Usually double output of standard lamp, around 3000-5000 lumens, common in high bay application.

  • IALD-International Association of Lighting Designers

    IES-Illuminating Engineering Society. Comprised of volunteer members from lighting manufacturers, designers, and test agencies, the IES creates the standards by which light and light products are measured and characterized.

    IES file (.ies extension)-The photometric file itself is an ASCII (delimited text) file. There are three formats: IES; EULUMDAT; and TM-14. In 1986 the Illuminating Engineering Society of North America (IESNA) created the standard LM-63-86, “IES Recommended Standard File Format for Electronic Transfer of Photometric Data.”  It is used for lighting design.

    Incandescent-A lamp that produces light by a filament heated to incandescence by an electric current and is not colored and meets certain other shape, size and wattage specifications.  The oldest electric lighting technology, widely used in residential lighting; poor efficiency, short lifespan; gradually being phased out in most countries.


    Kalvin temperature-A unit of measure for temperature based upon an absolute scale (i.e. 3,500K).

    kWh-The kilowatt-hour is a unit of energy equal to 1,000 Watt- hours. That’s what a 1,000W device uses in one hour – or what a 1W device uses in 1,000 hours. It’s the unit of measure used to compile your electricity bill.

    Lamp holders-Also known as sockets or tombstones (G13 base for TLED).  A device intended to hold an electric light bulb mechanically and provide electrical connections to the lamps and support it in the lighting fixture. The use of sockets allows lamps to be safely and conveniently replaced (re-lamping).

    Leading Edge Dimmer-Leading edge dimmers are the most common type of phase-cut dimmer, often as a replacement for a wall switch and are used to vary the amount of voltage to a screw-base light source.

    LED-Light Emitting Diode. A semiconductor device that emits visible light when an electric current pass through it. LED lighting is more energy-efficient than incandescent and fluorescent lighting. Widely regarded as the future of lighting. Semiconductor based, long-life span, highly efficient, versatile, durable.

    LED chip or die-The LED chip is a semiconductor device that emits incoherent optical radiation that may be in the ultraviolet, visible, or infrared wavelength regions. There is not a standardized process to make LED chips that takes the substrate and grows a layer of crystals with a complex combination of gases at a particular temperature. The process is complex, capital-intensive and requires high-caliber human resource capacity.

    LED Driver-An LED driver is a device which controls the amount of power to an LED, protecting it from sudden increases in voltage. Drivers are required to use low voltage LED bulbs. Similar in concept to a ballast, though a driver may be integrated into an LED bulb.

    LED light engine-A subsystem of a LED luminaire that includes one or more LED packages, or a LED array, or LED module; and LED driver; electrical and mechanical interfaces; and an integral heat sink to provide thermal dissipation.

    LED package-LED packages refer to the assembly of one or more LEDs, including the mounting substrate, encapsulant, phosphor if applicable, electrical connections, and possibly optical components, along with thermal and mechanical interfaces.

    LFL-A linear fluorescent lamp.  Generally comes in tubular form factor T12/ T8/ T5 with the numeric number indicating the diameter size in millimeter.

    Light-emitting diode (LED) chip Lm/W-When voltage is passed over the chip, electrons cross and emit energy in the form of light Lumens per Watt.

    LM-79 report-Measures an LED luminaire or integral lamp as a whole system according to a standard process using specified equipment. The testing report issued according to a standard format will provide:
    • Total Luminous Flux
    • Luminous Intensity Distribution
    • Electrical Power Characteristics
    • Luminous Efficacy (calculated)
    • Color Characteristics (CRI, CCT)

    LM-80 report-Used for measuring lumen maintenance of LED light sources. LM-80 applies to the LED package, array, or module alone, and is not a complete system. It is testing a component level based on data gathered from an LED manufacturer.

    LM-70 report-Used to measure the hours needed to reach 70% lumen maintenance. The data is collected over a period of 6000 to over 10,000 hours.

    Lumen Units of luminous flux-Luminous flux is a measurement of the visible intensity of a source of light. Lighting fixtures are measured by their lux output which is lumens per square meter.

    Luminaire-This is the complete lighting unit that integrates LED components and is directly connected to an electrical branch circuit. It consists of a light source and driver, along with parts to distribute the light, and to connect, position, and protect the light source. Luminaires can contain from one up to several hundred LED packages.

    Lumen depreciation-The luminous flux lost over time, and thus the complement of lumen maintenance.

    Luminous efficacy-Used to describe the efficiency of a light source. It compares light output (measured in lumens) to the amount of power used (measured in Watts). This gives the unit lm/W, which stands for lumen per watt. LED lights have a high number of lm/W.

    Lumen maintenance-Characterizes the amount of light produced from a light source or from a luminaire when it is brand new to the amount of light output at some time in the future, when the aged light source will likely be producing less light.

    Lux-Lux is the international unit of illuminance – a measure of how much luminous flux (in lumens) is spread over a given area (in square meters). In other words, it tells you how much light is arriving at a surface. 1 lm/m2 equals 1 lx. Multiply an illuminance figure in lux by an amount of time in hours and you have a measure of exposure in lux hours – useful if you’re looking after delicate objects or surfaces that can’t be exposed to too much light.

    MTBF-Mean time between failures is a measure of how reliable a hardware product or component is. For most components, the measure is typically in thousands or even tens of thousands of hours between failures. High MTBF are required for military usage.

  • NGLIA-Next Generation Lighting Industry Alliance.

    NIST-National Institute of Standards and Technology.

    OLED-An organic light-emitting diode (OLED), the electroluminescent material comprising the emissive layer of the diode is an organic compound. The organic material is electrically conductive due to the delocalization of pi electrons caused by conjugation over all or part of the molecule, and the material therefore functions as an organic semiconductor. The organic materials can be small organic molecules in a crystalline phase, or polymers.
    Phosphor conversion  A method used to generate white light with LEDs. Blue, or near ultra-violet LEDs are covered in phosphor, which glows white in reaction to the light produced by the LED.

    PIR-Passive Infrared detection device. In lighting, it is connected to a luminaire. A PIR detection device turns the light on or off when there is a large change in infrared activity, usually when someone enters or exits a room. This helps to save energy. PIRs are frequently used in security lighting.

    Power Factor (PF)-Power factor is a measurement of consumption efficiency.  It describes the ratio of real power consumed by a load to apparent power, or the Volt-Amp delivered to the load.

    Reflector Lamp-A bulb which has been silvered on its inside layer. It produces a soft-edged beam and is generally smaller in size than other lamps. Reflector lamps are available in a variety of colors and bases, so are suitable for any application.

    Resistance-A material’s opposition to the flow of electric current measured in ohms.

    Retrofit-A term used when new components are installed to upgrade existing lighting infrastructure.  Most commonly, when portions of a light fixture housing are kept, while electronics and light source are replaced.

    RGB-Stands for red, green, and blue; the three basic colors of light.

  • SiC-Silicon Carbide, a semiconductor related to GaN.

    SSL-Solid State Lighting is a term which refers to lights based on semiconductor opto-electronic devices. LEDs are a type of Solid State Lighting.

    Starter Switch-A starter switch is required to start fluorescent lamps. Unlike other forms of lighting, fluorescent lights need a starter switch to produce light and control their power.  Electronic ballasts are often used as alternatives.

    THD-Total Harmonic Distortion is a measurement of a electrical signal pollution that a load presents to a power system. THD is one characteristic used to describe the power quality of electric power systems such as ballast or driver.  High THD can cause disruptions in power service. THD is typically requires a special measurement device, though in some cases, lamps with poor THD will create noise that can be heard.

    TLED-Tubular LED, also known as linear LED, describes the form factor of the fluorescent replacement LED system.

    Troffer-A troffer is a rectangular light fixture that fits into a modular dropped ceiling grid (i.e. 2' by 2' or 2' by 4').  Troffer fixtures have typically been designed to accommodate standard fluorescent lamps (T12, T8, or T5), and can now be easily retrofitted with TLEDs to reduce even more power consumption.

    UL-Underwriters Laboratories. A global independent safety science company that provides safety-related certification, validation, testing, inspection, auditing, advising and training services to a wide range of manufacturers, retailers, policymakers, regulators, service companies, and consumers.

    UV light-Ultra violet light is found in sunlight and artificial light such as fluorescents.

    Volts-Unit of electro motive force.

    Watts-The standard delivered units of electrical power or energy per unit of time, measured in Joules per second. It is the starting point for how you are charged for energy.

    ZigBee-ZigBee is a global specification for digital radio communication that is suitable for applications that require a low data rate, long battery life and secure networks. Among those applications is lighting control. No special devices are needed to connect equipment to the lighting network. ZigBee is simpler and cheaper to implement than other wireless networks, such as Bluetooth.