You have the questions, we have the answers. The terms listed here are common lighting terms. This page provides a brief definition of these terms and how they relate to products designed for lighting applications.
- Accent Lighting - Accent lighting is directional lighting used to emphasize a particular object, location or area.
- AlInGaP - Aluminum indium gallium phosphide is a semiconductor material used in the manufacture of HB LEDs in red, orange, green, and yellow color, to form the heterostructure emitting light. It is also used to make diode lasers.
- Ambient Light - Ambient light is the light diffused in the environment. When measuring a particular light source, the existing light in the environment, which is not being emitted from the source, is considered ambient light.
- Ampere (Amp) - The unit for measuring an electric charge per second, known as current.
- Backlight - A backlight is any light source used to illuminate a panel or legend from behind. LEDs are becoming the most common form of light source in backlighting, widely used in illuminating small LCD panels.
- Ballast - A ballast is a device intended to limit the amount of current in an electric circuit. They can be as simple as a series resistor as commonly used with small neon lamps or as complex as the computerized, remote-controlled electronic ballasts used with fluorescent lamps.
- Binning - Binning is a subdivision of the manufactured product into specific performance parameters such as flux, color, and forward voltage. Binning puts parts into smaller groups in order to meet specific requirements of assembly.
- Candela - The candela (cd) is the SI base unit for luminous intensity. The operational definition of the candela describes it as the luminous intensity in a given direction of a monochromatic light source of frequency 540*10^12 Hz and a radiant intensity of 1/683 watt per steradian in that direction. When measuring the luminous intensity of light sources with different spectral content, a standard luminosity function is used as a correction factor. For reference, the luminous intensities produced by a common candle and a 100W incandescent bulb are approximately 1cd and 120cd respectively. Note that LEDs are often rated in millicandela (mcd).
- Candle Power - Old definition of luminous intensity. One candle power was the intensity of a standard whale wax candle burning at 120 grains per hour. Candela is the same as candle power, 1 candela = 1 candlepower.
- CCFL - Cold cathode fluorescent lamps (CCFLs) refers to light sources such as neon lamps that are based on gas discharge principles, where the cathode of the lamp is not independently heated. CCFLs remain popular for LCD backlighting and computer case modification.
- Chromaticity - Chromaticity refers to the aspect of color quality in terms of, wavelength, hue, saturation, and purity.
- Color Temperature - Color temperature refers to the numerical value given to a color in Kelvin (K) that describes a color as "warm"or "cool". High color temperatures (> 4000 K) are considered cool and are blue-green in hue. Lower color temperatures (< 3000 K) are considered warm and are yellow-red in hue. Light between 3000 K and 4000 K is considered neutral or pure. Cool light produces higher contrast and is considered better for visual tasks. Warm light is preferred for living spaces because it is considered more flattering to skin tones and clothing.
- Contrast - Contrast is the relationship between the luminance of an object and its background.
- CRI - Color Rendering Index.
- Die - The die is the very center or the heart of the LED.
- Diffuse Lens - Diffuse lenses have a semi-transparent appearance which makes the LED appear dimmer, but gives a wider viewing angle of the light than "waterclear" lenses.
- Diffuser - A diffuser is an optical element used to mix light rays to improve uniformity.
- Dimmer - A control which varies the output of a light source by reducing the voltage or current to the lamp.
- Diode - Most modern diodes are based on semiconductor p-n junctions. In a p-n junction, conventional current can flow from the p-type side (the anode) to the n-type side (the cathode), but cannot flow in the opposite direction.
- Dominant Wavelength - The wavelength at which the human eye perceives the light emitted from the LED to be the strongest.
- Driver - Generally, any device used to condition or control some quantity in order to provide another device with an appropriate input. In the lighting sector, an LED driver is most often a device used to control the forward current flowing through one or more LEDs.
- Foot-Candle - A foot-candle is a unit of measurement for illuminance, or the intensity of light that is incident upon a surface. It can be defined as the intensity of light resulting from 1 lumen of luminous flux being distributed uniformly across a surface with an area of 1 square foot.
- HB LED - High Brightness Light Emitting Diodes (HB LEDs) is a loosely defined term generally referring to LEDs capable of producing large amounts of luminous flux for illumination applications, and which are generally operated at much higher power levels than LEDs used for indication purposes.
- Heat Sink - A heat sink is a metal device that uses thermal contact to absorb and dissipate thermal energy from a high temperature object to a lower temperature object that has a much greater heat capacity. This process acts as a cooling mechanism because of thermal equilibrium. Heat sinks are typically designed with many fins in order to maximize surface area for a rapid transfer of thermal energy to the surrounding cooler air.
- Incandescent - Relating to emission of light by a hot object due to its temperature. An incandescent lamp is one which produces light by heating a filament until it radiates electromagnetic energy in the visible spectrum.
- Infrared (IR) - The invisible portion of the electromagnetic spectrum which the wavelength is longer than visible light and extends from the range of 750 nm to 1 mm.
- Laser - An acronym of Light Amplification by Stimulated Emission of Radiation. A very high energy beam of light that remains very parallel throughout its length. Must use caution when operating, can cause permanent damage to the retina of the eye.
- LED - A light-emitting diode (LED) is a semiconductor diode that emits light when an electrical current is applied in the forward direction of the device. The effect is a form of electroluminescence where incoherent and narrow-spectrum light is emitted from the p-n junction. LEDs are widely used as indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. An LED is usually a small area (less than 1 mm²) light source, often with optics added to the chip to shape its radiation pattern and assist in reflection. The color of the emitted light depends on the composition and condition of the semi conducting material used, and can be infrared, visible, or ultraviolet.
- LED Circuit - The basic LED circuit is an electrical circuit used to power an LED. It consists of up to four components connected in series: a voltage source, a current limiting resistor, a LED, and optionally a switch to open and close the circuit. Two diodes may be placed in parallel in the circuit, but connected anode to cathode; the second diode may be used to protect the LED against reverse bias, which can damage the LED, or it may be another LED which is illuminated when the polarity of the voltage source is reversed. The LEDs used will have a forward voltage specified at the intended operating current. Ohm's law, V=IR, is used to calculate the resistor that is used to attain the correct current. The resistor value is computed by subtracting the forward bias voltage from the supply voltage, and then dividing by the desired operating current.
- Lens - An optical lens is an optical device with axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens is a lens consisting of a single optical element. A compound lens is an array of simple lenses (elements) with a common axis; the use of multiple elements allows more optical aberrations to be corrected than is possible with a single element. Manufactured lenses are typically made of glass or transparent plastic.
- Light Engine - A light engine is generally one or more high-brightness LEDs in a pre-fabricated array that is used for illumination applications.
- Light Pipe - A light pipe is an optical conduit that is used to pass light from one location to another. These devices come in many arrangements including single, multiple, and panel mount. Light pipes protect circuits from electrostatic discharge (ESD) by isolating the device’s front panel from the circuit board.
- Lumen - The lumen (lm) is the SI unit of luminous flux and is defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian.
- Luminous flux - The measure of the perceived power of light emitted in all directions. It differs from the measure of the total power of light emitted since luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. In other words, luminous flux is a weighted sum of the emitted power at all wavelengths in the visible band.
- Luminous Intensity - The measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd).
- MCPCB - A Metal Core Printed Circuit Board (MCPCB) incorporates a base metal material as a means for heat dissipation. The metal core usually consists of an aluminum alloy.
- Nanometer - Unit of measurement, abbreviated nm. 1 billion nm is equal to 1 meter.
- OLED - An organic light-emitting diode (OLED) is an LED whose emissive electroluminescent layer is composed of a film of organic compounds. The layer usually contains a polymer substance that allows suitable organic compounds to be deposited in rows and columns onto a flat carrier by a simple "printing" process. The resulting matrix of pixels can emit light of different colors. Such systems can be used in television screens, computer displays, and portable system screens such as PDA's, advertising, information and indication. OLEDs typically emit less light per area than inorganic solid-state based LEDs and can degrade over time, but they do not require a backlight to function and can therefore be very thin. They also draw far less power and can operate longer on the same battery charge.
- Optics - An optical lens transmits or refracts light, converging or diverging the beam. The viewing angle of a lens controls how narrow or wide the beam of light is from an LED. Lenses have either a clear or diffused package which refers to how quickly the light dissipates at the edge of the viewing angle.
- Package Size - The package size of a surface mount component is typically written as a four digit number in units of hundredths of an inch or tenths of a millimeter. For example, "0402 (1005 metric)" would be 0.04"x 0.02"(1.0 mm x 0.5 mm).
- Peltier - The Peltier (or thermoelectric) effect refers to a current that creates a temperature difference between an upper and lower conductor. These conductors are attempting to recreate the electron equilibrium that existed before current was applied by absorbing energy at one conductor and releasing it at the other. A Peltier device can be used for both heating and cooling but is much more economical to be used for only cooling.
- Photometer - A photometer is a device used for measuring luminous intensity or luminance.
- PWM - Pulse-Width Modulation (PWM) of a signal or power source involves the modulation of its duty cycle to either convey information over a communications channel or control the amount of power sent to a load. Pulse-width modulation uses a square wave whose pulse width is modulated resulting in the variation of the average value of the waveform.
- RGB - The term RGB stands for red, green, and blue, the three primary colors of light. When the three colors are mixed the result of the color of light appears white to the human eye. By adjusting intensities of each color can produce all of the other colors in the spectrum.
- Seven-Segment Display - A seven-segment display is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays. Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic devices for displaying numerical information.
- Steradian - The steradian (sr) is the SI unit of solid angle. It is used to describe two-dimensional angular spans in three-dimensional space, analogous to the way in which the radian describes angles in a plane. The name is derived from the Greek stereos for "solid" and the Latin radius for "ray beam".
- Thermal Grease - Thermal grease is a thermally conductive compound that aids in the bonding of a heat sink to a device where heat dissipation is required, such as a microprocessor.
- Thermal Pad - Thermal pads are used as an interface for heat dissipation between a component to be cooled and a heat sink. Many factors influence the decision to use thermal pad including thermal and electrical conductivity of the material, long-term stability, reliability, and ease of application. The fundamental characteristic of a thermal pad is how it can soften at higher temperatures. This allows it to conform to the surfaces that it is bonded to which increases surface area for heat transfer.
- Thermal Tape - Thermal tape is a thermally conductive adhesive used to mount a heat sink to a device where heat dissipation is required, such as a microprocessor.
- UV (Ultra-Violet) - The invisible portion of the electromagnetic spectrum with the wavelength between 1nm and 400nm.
- Viewing Angle - The viewing angle refers to the cone shaped pattern in front of the light source. The viewing angle is determined to front and sides of the LED at which the light output falls off 50 percent.
- Visible Spectrum - The light spectrum between 400 nm and 700 nm which is detectable by the human eye.
- Watt - The unit for measuring electrical power. Watt does not relate to the light output level, instead it defines the rate of energy consumed by the device.
- Wavelength - Wavelength is the distance between repeating units of a propagating wave of a given frequency. It is measured in meters (m) and is commonly designated by the Greek letter lambda (λ). The wavelength is related to the frequency by the formula: wavelength = wave speed / frequency. Wavelength is therefore inversely proportional to frequency. Higher frequencies have shorter wavelengths while lower frequencies have longer wavelengths, assuming the speed of the wave is the same. Visible light ranges from deep red, roughly 700 nm (10-9 m), to violet, roughly 400 nm.