Light for Plants

LED and Lighting Terms Glossary


The positively charged electrode by which electrons leave an electrical device.

Application Specific (AS) LED Module

Sunlite’s modules have a very thin insulating layer and no air gap between the LED chip and the integrated glass lens.  These modules are easy to assemble and replace, and made specific to each application.

Can light

Can light is a light fixture that is installed into a hollow opening in a ceiling.  Also called a canister light, recessed light, or downlight.


The SI unit of luminous intensity.  One candela (cd) is 1 lumen per square meter.


The negatively charged electrode by which electrons enter an electrical device.

Chips on Board (COB) LED Module

A module that has multiple LED chips sharing the same package.  In a chips on board module, the LED chips are usually placed next to each other, creating a heat concentration problem.  COB has a thick insulating layer (as opposed to many insulating layers in a discrete module).  The optical lens in a COB module is typically flat, which creates a high reflection of the light being emitted by the package.

Color Rendering Index

Color Rendering Index (CRI) is a quantitative measure of the ability of a lamp or given light source to reveal (show) the colors of objects faithfully, as compared with an ideal or natural light source.  CRI is based on a 0-100 scale, and most LEDs have a CRI of 80 or higher.

Color Temperature

Color temperature (CCT) is a characteristic of emitted visible light, defined as the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source. It is measured in Kelvin (K).  Lower temperatures (2,700-3,000 K) are called warm colors (yellowish white through red), and higher temperatures (5,000+ K) are called cool colors (bluish white).

Color Tuning

Color Tuning refers to a change in the color temperature of white light, or the shade of white light.  Traditionally it was done using added color filters or with separately controlled warm and cool light fixtures.  Color Tuning can now be done through a single LED light fixture.

Compact Fluorescent Lamp (CFL)

A fluorescent light bulb that has been compressed into the size of a standard-issue incandescent light bulb; some types fit into light fixtures formerly used for incandescent lamps.  They typically last six times as long and use a quarter of the power of an equivalent incandescent light bulb.

Current Controlled Dimming

Current-controlled dimming controls LED brightness by varying the applied current using a 0-10V dimmer.  Current-controlled dimming is smooth and HD-video friendly. It can only dim to a minimum of 5% of light output.


Direct current, the unidirectional flow of electric charge, produced by power sources such as batteries.


In optics, a diffuser is a covering that diffuses, spreads out, or scatters light in some manner in order to give soft light.


A technology used by an LED driver to provide power and control to an LED board.

Dimming (PWM-Controlled)

PWM (Pulse Width Modulation) controlled dimming works by switching the LED on and off at a given frequency. LED is dimmed by reducing the time the light is on (the duty cycle).  PWM dims smoothly from 0% to 100% output.  Because of its digital nature, it can be easily incorporated in smart lighting control.  PWM is not HD video friendly.


A simple type of electronic device with two electrodes (terminals) that allows current to flow in one direction only.

Discrete LED Module

A module that has individually packed LEDs mounted on a PCB.  Each LED has its own optical lens and many insulating layers that act as barriers for heat dissipation.  Additional protection lenses are typically required with this type of LED module.

Edison Base

The “screw shaped” base of a light bulb originally designed by Thomas Edison.  It is used to hold the bulb in place and make contact with the power supply.


A piece of equipment or furniture that is fixed in position in a building or vehicle (a light fixture).

Fluorescent Lamp

A glass tube that radiates light when phosphor on its inside surface is made to fluoresce by ultraviolet radiation created from mercury vapor being bombarded  by electrons.


A unit of measure of the intensity of light falling on a surface equal to that given by a source of one candela at a distance of one foot.  Originally defined with reference to a standardized candle burning at one foot from a given surface.  Equal to 1 lumen per square foot.

Halogen Lamp

An incandescent lamp that has a small amount of a halogen gas such as iodine or bromine added.  They are able to operate at higher temperature than standard incandescent bulbs of similar power and operating life, thereby producing higher luminous efficacy and color temperature.

Heat Dissipation

Heat dissipation refers to how effectively generated heat is removed and eliminated from the LED and module.  60% of the power supplied to an LED is converted to heat.  More effective heat dissipation leads to increased LED efficiency and lifespan.


A body that holds, surrounds, and/or covers an LED light.  Sunlite housings are made of extruded aluminum.

Incandescent Lamp

A source of electric light that works by incandescence, the emission of light caused by heating a tungsten filament.  Commonly known as a light bulb.

Insulating Layers

Insulating layers are used to stabilize, connect, and protect the critical components of an LED module.  More insulating layers used in and around the LED module, PCB board, and fixture will greatly reduce heat dissipation, leading to decreased LED efficiency and lifespan.

Junction Box

A container for electrical connections, usually intended to conceal them from sight and to deter tampering.  A junction box may form part of an electrical conduit or wiring system in a building.


A light-emitting diode.

LED Chip

A semiconductor chip that is the heart of the LED.  It converts electricity into light at the PN junction.

LED Driver

A switching power supply that converts AC voltage to DC, or adjusts DC voltage supplied to an LED.

LED Driver (Fixed Current)

A fixed current driver supplies constant current to an LED.  Fixed current drivers are more costly and complicated than fixed voltage LED drivers, but they are efficient and good at minimizing brightness variation between LEDs.  Fixed current drivers can directly drive high-power LEDs.

LED Driver (Fixed Voltage)

A fixed voltage driver supplies constant voltage to an LED.  Fixed voltage drivers are simple and cost efficient. When a fixed voltage driver is used on LEDs in parallel, the current varies based on the different Vf (forward voltage) of each LED and the heat generated by the LED, resulting in a different brightness of each LED.  A fixed voltage LED driver is typically used for low-power LEDs (such as a tape light), or on high-power LEDs that have a constant current board to regulate current.

LED Light spectrum

The color of light emitted from an LED is determined by the PN junction material.  LEDs can naturally emit light from 360nm to 940nm.  White light is typically made by applying yellow, green, and red phosphors to blue LEDs.

LED Module

A unit that supplies a light source.  In addition to one or more LEDs it may contain other optical, mechanical, electrical, and electronic components.

LED Package (Through-the-Hole)

LED packages that are low power, such as the T-1¾ LED package or high flux LED package.

LED Package (Surface Mount Device (SMD)

SMD LED packages typically use low or medium power.

LED Package (High Power)

LED packages using surface mount technology (SMT), a method that involves mounting components directly onto the surface of printed circuit boards (PCBs).

LED Package (Application Specific (AS)

AS LED packages are specific to an application.  Sunlite has patented a method of mounting LED chips directly onto a heat sink, and makes application specific LED packages.  These AS-LED packages (modules) are used for specific applications and are easy to assemble and replace.

Surface Mount”Technology (SMT)

A method that involves mounting components directly onto the surface of printed circuit boards (PCBs).

LED Package (Application Specific (AS)

AS LED packages are specific to an application.  Sunlite has patented a method of mounting LED chips directly onto a heat sink, and makes application specific LED packages.  These AS-LED packages (modules) are used for specific applications and are easy to assemble and replace.

LED Wafer

LED wafer is a semiconductor wafer with light-emitting P-type and N-type semiconductor materials grown on a semiconductor substrate such as silicon or sapphire.  LED wafers are metalized and cut into LED chips.


A lifetime test used for LED lights and a measure of the usable light level, defined as the length of time at which the light fixture has dimmed to 70% of its original output.


The SI unit of luminous flux.  One lumen (lm) is equal to the amount of visible light emitted in a solid angle of 1 steradian, from a source that radiates in all directions whose intensity is 1 candela (cd).

Lumen Depreciation

The principle that every light source gets dimmer over time as it is used.  LEDs don’t fail in the same way as other lighting technologies.  They get dimmer and dimmer over time and other parts of a light fixture will likely fail before an LED goes completely out.

Lumen Maintenance

The difference between a fixture’s initial and end of life brightness.  For example, if a fixture has a lumen maintenance of 90%, that would mean that it lost 10% of its brightness during its rated lifespan.

Lumens per Watt

The SI units of Luminous Efficacy.  Lighting efficiency is measured in lumens per watt (lm/W).


A unit of illumination.  10.76 lux = 1 foot-candle.


Used in fabricating LED chips, Metal Organic Chemical Vapor Deposition (MOCVD) is a technique used to deposit very thin layers of atoms onto a semiconductor wafer.

Parallel circuit

A closed circuit in which the current divides into two or more paths before recombining to complete the circuit.  Each load connected in a separate path receives the full circuit voltage, and the total circuit current is equal to the sum of the individual branch currents.

Phase-Controlled Dimming

Phase-controlled dimming commonly uses a TRIAC dimmer.  TRIAC dimmers are designed for more resistive loads such as those of incandescent and halogen lamps.  It is not efficient for LED and will cause flickering.


A synthetic fluorescent or phosphorescent substance that exhibits luminescence when struck by light of certain wavelengths.

PN Junction

A PN junction is formed between a P-type semiconductor and an N-type semiconductor.  When current passes through the junction, electrons are pushed to the P-zone where they recombine with the electron hole to emit light.  The wavelength of the light and color emitted is determined by the materials of the PN junction.


A potentiometer is an instrument with a manually adjustable voltage divider or variable resistor used for measuring, comparing, or controlling power output.  A potentiometer is useful for testing LED products and color tuning.

Printed Circuit Board (PCB)

The circuit board base (or substrate) for physically supporting and wiring the surface-mounted and socketed components in most electronics.  PCBs generally have thermal properties to disperse heat.

Retrofit LED

Retrofit LEDs are direct replacements for conventional incandescent, halogen, and CFL lamps that can be fit into, or onto, existing equipment. Retrofit LEDs typically have a compact AC to DC driver built in.  Both the LED and the driver create heat that dissipates through the same heat sink.  Dimmable retrofit LEDs often have flickering problems.

Series circuit

A closed circuit in which the current follows one path.  In a series circuit, the current through each load is the same and the total circuit voltage is the sum of the voltages across each load.


A hard, unreactive, colorless compound that occurs as the mineral quartz and as a principal constituent of sandstone and other rocks.


Any of numerous compounds containing silicon, oxygen, and one or more metals.


A chemical element with semiconducting properties often used in making electronic circuits.


Polymers that include any inert, synthetic compound made up of repeating units of siloxane.

Smart Lighting

A smart lighting system automatically controls and adjusts light based on the surrounding environment and position or movement of nearby persons.  Smart lighting can be further integrated into an Internet of Things (IOT) system.

Solid State Lighting

Solid state lighting (SSL) refers to lighting applications that use light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), or light-emitting polymers. Unlike incandescent or fluorescent lamps, which create light with filaments and gases encased in a glass bulb, solid-state lighting consists of semiconductors that convert electricity into light.


A test of the lifetime value for an LED.  TM-21 values are generally reported as 6-times the number of LM-80 test hours (the elapsed operating time at which the specified percentage of the lumen maintenance is reached, expressed in hours).

Underwriters Laboratories (UL)

An American worldwide safety consulting and certification company headquartered in Illinois.  UL provides safety-related certification, validation, testing, inspection, auditing, advising, and training services to a wide range of clients.  Sunlite uses UL for testing its products.


A description of the smoothness of the lighting pattern or the degree of intensity o light and dark areas in the area to be lighted.  Uniformity is usually expressed as a ratio such as max to min.  The lower the ratio the more uniform the lighting design.

Visible Light Spectrum

The visible light spectrum generally refers to the spectrum from 400nm to 800nm.  Below 400nm is the UV spectrum; UV light generally fades and discolors material.  Above 800nm is the infra-red spectrum; infra-red causes radiant heat.