Glossary of LED Lighting Terms

The temperature of the air surrounding the device.

A measure of electrical current. Amps = Watts/Voltage

An average rating, in hours, indicating when a large group of lamps have failed, when operated at nominal lamp voltage and current. The life of an LED is defined as the operating time in hours for the lamp to reach L70 which designates 70% lumen maintenance (or 30% reduction in initial lumen output).

Refers to a lamp, such as an LED, with a special phosphor or coating to give it a color rendering profile similar to natural daylight.

A lamp’s ability to render an object’s true colors based on a scale of 100.

A numerical measurement of the color appearance of a light source measured in degrees Kelvin (K). It also refers to the way color groups are perceived (psychological impact of lighting) with “warm” colors at the red/orange/yellow end of the spectrum and “cool” colors at the blue end.

Chromaticity is the quality of a colour or light in reference to its purity and its dominant wavelength, or in simple terms, its departure from white light. The CIE Chromaticity Chart is a standard color space. In 1931, CIE defined a human color standard, based on measurements of the color-matching abilities of the average human eye. Using data from laboratory measurements, a system of three primaries, XYZ, was developed in which all visible colors can be represented using only positive values of X, Y and Z. The Y primary is identical to Luminance, X and Z give color (chroma) information.

A measure of the rate of flow of electricity, expressed in amperes (Amps).

A two-terminal semiconductor device having a positive-negative (p-n) junction which mainly allows energy to travel in one direction.

An LED driver is a self-contained power supply that has outputs which match the electrical characteristics of the LEDs.

An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. Electrolytic capacitors produce excessive amounts of heat that often lead to failures in most LED lamps. They are used in relatively high-current and low-frequency electrical circuits, particularly in power supply filters, where they store charge needed to moderate output voltage and current fluctuations in rectifier output. They are also widely used as coupling capacitors in circuits where AC should be conducted but DC should not. There are two types of electrolytics: aluminum and tantalum.

A unit of illuminance or light falling onto a surface measured as the light level on a surface one foot from a standard candle.

A heat sink is an object that absorbs and dissipates the heat generated by the operation of an LED lamp.

Light falling on a surface, expressed in lumens per unit area; 1 lumen per square foot equals 1 footcandle, while 1 lumen per square meter equals 1 lux.

The measured luminous output of a new LED light source.

IC-based CFLs operate by controlling the voltage and current by adjusting the output frequency which provides stable operation of the CFL. Controlling the current produces less stress on the cathode and the electronic components, which results in long life, smoother dimming, and less noise.

Light temperature term – using the symbol (K) – to indicate the comparative color appearance of a light source when compared absolute black. Warm incandescent lamps are 2700K. Halogen and other light sources range from 3000K to 7500K and higher.

Short for light-emitting diode. An LED is an electronic semiconductor device that emits light when an electric current passes through it. LEDs are considerably more efficient than incandescent and halogen bulbs, and rarely burn out.

An electronic circuit that converts input power into a current source — current should remain constant despite fluctuations in voltage. Most LED drivers use an Electrolytic Capacitor to achieve constant surrent. The LED driver protects LEDs from normal voltage fluctuations, over voltages, and voltage spikes.

A lens is an optical device that refracts light, converging or diverging the beam.

A low voltage lighting system usually operates on 12 volts. An electric or magnetic low voltage transformer is used to convert line voltage, or high voltage, (110/120 Volt) from a home or commercial building and steps it down to 12 Volts.

A measure of luminous flux or quantity of light emitted by a LED lamp.

The gradual decline in light output from a solid state light source over time due to LED darkening.

A measurement of how a lamp maintains its light output over time. Generally, lumen maintenance is a comparison of the amount of light produced from an LED lamp when it is brand new to the amount of light output at a specific time in the future.

A measure of the efficacy (efficiency) of a light source. The number is achieved by dividing lumens produced by watts consumed.

The light output (lumens) of a light source divided by the total power input (watts) to that source. It is expressed in lumens per watt.

A unit of illuminance or light falling onto a surface. One lux is equal to one lumen per square meter.

An inorganic chemical compound processed into a powder and deposited on the inner glass surface of fluorescent tubes, CFL’s, LED’s and some mercury and metal-halide lamp bulbs.

The length of time of a statistically large sample between first use and the point when 70% of the LEDs on a lamp have failed.

Lighting devices that do not rely on chemical reactions to produce light.  Most SSL lamps do not contain filaments or parts that can break, rupture, shatter, leak or contaminate the environment.

The method of controlling the operating temperature of the product by designing a path for heat to leave the body of the lamp using heat sinks and improved airflow.

A measurement of the electromotive force in an electrical circuit or device expressed in volts.

A unit of electrical power. Lamps are rated in watts to indicate the rate at which they consume energy.