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Glossary of LED Terms

Glossary of LED Terms

A | B | C | D | E | F | I | L | M | N | O | P | R | S | T | V | W | Z |

Active component

A component that changes the amplitude of a signal between input and output.

Ambient Temperature (Ta)

The surrounding temperature within an environment.


The positively charged terminal or electrode toward which electrons flow.


Abbreviation for “American Wire Gauge.” A gauge that assigns a number value to the diameter of a wire.


Use of an LED as a light source to illuminate a lens or legend from behind without protrusion through the panel.


The faceted collar of a panel-mount LED indicator visible from the front.

Bi-Color LED

A single LED device containing two different colored LED dice. The different colored dice can be illuminated independently or together.


During fabrication, LEDs grow in the form of a crystal wafer. A 2-inch diameter wafer can carry more than 20,000 LED chips. Color and intensity variations are common across a wafer. LEDs can be “binned” into various groups by wavelength, luminous intensity, voltage drops, and other characteristics.

Bridge Rectifier

A circuit using four diodes to provide full wave rectification by converting an AC voltage to DC voltage.


A unit of luminous intensity equal to 1/60th of the normal intensity of one square centimeter of a blackbody radiating at the temperature of solidification of platinum.

Candle Power

Luminous intensity expressed in candelas.


The terminal or electrode that is negatively charged and from which electrons flow.

CIE Chromaticity Diagram

In 1931 (Commission Internationale de l’Eclairage (CIE) established the X-Y-Z tristimulus system for measuring color properties, based on the assumption that every color is a combination of three primary colors: red, green and blue. The CIE Chromaticity Diagram is a two dimensional color space that defines all of the colors perceived by the human eye. Pure colors are located on the extreme outer edges of the diagram and white is located in the center.

Continuous Forward Current

The maximum continuous operating current the LED can withstand without diminishing its operating life.


Measured in amperes, it is the flow of electrons through a conductor. Also know as electron flow.

Current-Limiting Resistor

A resistor is added in series between the power source and the LED to regulate the current delivered to the device (see Ohm’s Law).


The chip within the LED package; the plural form is dice.

Diffused Encapsulation

Glass particles are suspended within the epoxy lens of the LED diffusing the light over a wide viewing area. The encapsulation may be white or colored to match the LED output.


A two terminal device that conducts in only one direction.

Dominant Wavelength (λd)

A measure of the hue sensation perceived by the human eye.


The conversion of electrical energy into light via non-thermal means.

Electrostatic Discharge (ESD)

A sudden redistribution of static charge which can be damaging to sensitive components.

Flow Soldering

Flow or wave soldering technique in large scale electronic assembly to solder all the connections on a printed circuit board by moving the board over a wave of molten solder.

Foot Candle

A measure of illumination in which one unit equals the amount of light delivered by a one-candela light source to a one square-foot surface one foot away.

Forward Bias

A P-N junction bias which allows current to flow through the junction. Forward bias decreases the resistance of the depletion layer.

Forward Current

Current through a diode in the direction of its greatest conduction.

Forward Voltage (Vf)

The operating voltage of the LED. The typical rating is the voltage at which the LED will light. The maximum rating is the voltage that, if exceeded, will diminish LED lifetime.

Fresnel Lens

A thin optical lens consisting of concentric rings of segmental lenses and having a short focal length.

Incandescent Lamp

A light source where voltage passes through a filament to create heat which, in turn, creates light.

Lamp Size

Industry standard classifications for lamps sizes are based on descriptive designators referring to the diameter of the lamp. “T-1” is the base designation for a 1/8” diameter lamp. Other designations are based on the T-1 standard, i.e., T-1¾ is 1¾ multiplied by 1/8, or .219”.

Lead Frame

Lead Frame

Light-Emitting Diode (LED)

A light-emitting diode (LED) is a solid-state semiconductor device that converts electrical energy directly into light.

Luminous Flux

is defined as the total electromagnetic energy emitted by the light source into a sphere (360°) surrounding the light source.

Luminous Intensity (Iv)

Luminous Intensity is equal to the amount of luminous flux emitted into a very small solid angle at a defined angular orientation from the light source. The measurement for luminous intensity is the lumen or candela.

Mean Spherical Candle Power (MSCP)

The average luminous intensity of a lamp illuminating in all directions. The measurement is made by placing the lamp in the center of a sphere.

Millicandela (mcd)

One thousandth of a candela.

Nanometer (nm)

The nanometer (one-billionth of a meter) is the measurement unit for peak wavelength. Visible light falls in the range of 380 to 700nm.


Unit of resistance symbolized by the Greek capital letter omega (O).

Ohm’s Law

Relationship between voltage, current and resistance. Ohm’s law states that current in a resistance varies in direct proportion to voltage applied and inversely proportional to resistance.

Operating Current

The amount of current an LED is designed to draw from the power source.

Operating Temperature

The temperature range over which an LED is designed to operate safely.

P-N Junction

The positive-negative junction of a semi-conductor diode. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.

Passive Component

A Component that does not amplify a signal. Resistors and capacitors are examples.

Peak Forward Current

Forward current driven during pulse operation.

Peak Wavelength (λpk)

Peak Wavelength is defined as the single wavelength of saturated color at the peak of the radiated spectrum.


An instrument for measuring a property of light, especially luminous intensity or flux. A photometer uses special colored filters to replicate the response of the human eye. Light intensity is measured in candle power, usually by comparison with a standard source.

Power Dissipation

Amount of heat energy generated by a device in one second when current flows through it.

Printed Circuit Board

Insulating board containing conductive tracks for circuit connections.


Symbolized “R” and measured in ohms. Opposition to current flow and dissipation of energy in the form of heat.


Component made of material that opposes flow of current and therefore has some value of resistance.

Reverse Breakdown Voltage

Amount of reverse bias that will cause a P-N junction to break down and conduct in the reverse direction.

Storage Temperature

The temperature range over which an LED is designed to be stored safely in the off-state.

Surface-Mount (SMT) LED

SMT LEDs are soldered to the surface of the circuit board. The LED die is integrated into the package design. SMT components can be assembled faster and with better quality than through-hole components.

Through-Hole LED

This kind of package is soldered “through holes” to the circuit board. The LED chip is seated in a reflector and light is emitted by a lens integrated into the package. Different radiation characteristics are produced as a function of chip-to-lens spacing and the shape of the lens.

Tinted Encapsulation

Color added to the LED epoxy lens to identify the LED color when it is in the off-state. The tint does not affect the luminous intensity or viewing angle.

Tri-Color LED

A single LED device containing two different colored LED dice and three leads. The different colored dice can be illuminated independently or together with a common anode or cathode.

Viewing Angle

Viewing Angle is the total cone angle in degrees encompassing the central, high luminous intensity portion of the LED beam from the on-axis peak to the off-axis point where the LED intensity is 50% of the on-axis intensity. This off-axis point is known as theta one-half (? 1/2). Two times ? 1/2 is the LEDs’ full viewing angle; however, light is visible beyond the ? 1/2 point.

Voltage Drop

Voltage or difference in potential developed across a component due to current flow.

Voltage (V)

Term used to designate electrical pressure or force that causes current to flow.

Waterclear Encapsulation

An LED lens without tint or color. The LED color cannot be determined in the off state.

Wavelength (λ)

Distance between two points of corresponding phase and is equal to waveform velocity divided by frequency.

Zener Diode

Semiconductor diode in which reverse breakdown voltage current causes the diode to develop a constant voltage. Used as a clamp for voltage regulation.

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