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Glossary of LED Component Terms

Below is a list of definitions of various types of technologies used in optoelectronic industry, the components they are made of and other useful definitions you may come across when browsing this website or other sources on LED industrial .

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Active component:

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


One of the material systems for manufacturing LEDs that produce light in the red and amber portions of the visible light spectrum.


The preferred LED (Light Emitting Diode) chip technology containing Aluminum, Indium, Gallium, and Phosphorous to produce red, orange and amber-colors.

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.


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


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.


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

Bi-Color LED:

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

Bridge Rectifier:

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


Often used incorrectly with respect to illumination as a synonym for luminous flux, an objective measurement of the visible power of a light source. The term is correctly used when describing screen brightness in a display or television.


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.

Color temperature

The description used to describe the effect of heating an object until it glows incandescently, the emitted radiation, and apparent color, changes proportional to the temperature; easily envisioned when considering hot metal in a forge that glows red, then orange, and then white as the temperature increases.

Continuous Forward Current:

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

Cool White:

A description of a range of correlated color temperatures.


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.


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.


A hard rugged epoxy surrounding the LED die, provides diffusion & lensing of the LED light.


Organic polymer frequently used for a dome or lens, often prone to optical decay over time, resulting in poor lumen maintenance. High quality LEDs such as LUXEON contain no epoxy in the optical system and deliver superior lumen maintenance.

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.

Flux / Luminous Flux:

Luminous flux is the measure of the perceived power of light, adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light

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.

ward 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.

High Power LED

A high power LED, sometimes referred to as a power LED, is one that is driven at a current of 350 mA or higher.


High-brightness is a term that is often applied to an LED but has no measured meaning and does not indicate any level of performance.


The intensity of light falling on a surface area. If the area is measured in square feet, the unit of illuminance is footcandles (fc). If measured in square meters, the unit of illuminance is lux (lx).

Incandescent Lamp:

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

Infrared (Near):

Electromagnetic radiation with wavelength range from 700 nm – 3000 nm.


The preferred LED (Light Emitting Diode) semiconductor material system containing Indium, Gallium, and Nitrogen to produce green, blue and white-colored LED light sources.

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”.

LED Array:

An assembly of LED packages or dies on a printed circuit board or substrate, possibly with optical elements and additional thermal, mechanical, and electrical interfaces that are intended to connect to the load side of an LED driver.

LED Chip (Chip):

The light producing semiconductor device that may or may not be incorporated into an LED.

Light-Emitting Diode (LED):

A Light Emitting Diode (LED) is a solid-state semiconductor device that converts electrical energy directly into light. On its most basic level, the semiconductor is comprised of two regions. 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.

LED Luminaire:

A complete lighting unit consisting of LED-based light emitting elements and a matched driver together with parts to distribut light, to position and protect the light emitting elements, and to connect the unit to a branch circuit. The LED based light emitting elements may take the form of LED packages, (components), LED arrays (modules) LED Light Engine, or LED lamps. The LED luminaire is intended to connect directly to a branch circuit.

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.

Luminous Flux:

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

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.

Organic Light-emitting Diodes (OLED):

Organic light-emitting diodes (OLEDs) are based on organic (carbon based) materials. In contrast to LEDs, which are small point sources, OLEDs are made in sheets which provide a diffuse area light source. OLED technology is developing rapidly and is increasingly used in display applications such as cell phones and PDA screens. However, OLEDs are still some years away from becoming a practical general illumination source. Additional advancements are needed in light output, color, efficiency, cost, and lifetime.

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.

RGB Color Model:

An additive color model in which red, green, and blue light are added together in different proportions to produce a broad range of colors, including white.

RGB White:

A method of producing white light by combining the output from red, green, and blue LEDs.


Surface-mount LEDs.

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.

Thermal management:

Controlling the operating temperature of the product through design, examples includes heat sinks and improved airflow.

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.

Tunable White Light:

White-light LED fixtures that combine channels of warm white and cool white LEDs to produce a range of color temperatures.

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 (V):

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

Voltage Drop:

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

Warm White:

A description of light with a correlated color temperature between 3000K and 3500K, usually perceived a slightly yellow.

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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