What is Light?

Definition of Light
Light is electromagnetic radiation detectable by the human eye. Visible light occupies and is defined by a range of frequencies called the Visible Light Spectrum. The Visible Light Spectrum is usually expressed in terms of nanometers (nm) of wavelength rather than frequency in Hertz. In the lighting industry, the conventional range of the wavelengths for visible light is about 400 nm to 700 nm, as shown in the Visible Light Spectrum image.

Lighting Terminology
There is a unique vocabulary or terminology used to describe and measure various aspects of light. The Photometric Measurement of Light graphic lists some photometric terminology commonly used in the lighting business. For example, illuminance and luminance are common photometric terms that are similar but not the same.

What is an LED?

Light emitting diodes (LEDs) are solid-state lighting components with no moving, fragile parts. LEDs, which may last for decades, are much more energy efficient than light bulbs, depending on the application. In television sets, vacuum tubes were replaced with solid-state components; similarly the last remaining vacuum tube light bulbs are now being replaced by solid-state components.

Just picture a grain of sand emitting a bright light - usually red, amber, green or blue- when an electrical current is applied. Basically that's an LED. While the manufacturing process to develop an LED is somewhat complex, the principle is rather simple.

Why LED?

Long Useful Life - 70,000 Hours / 10 years have been reported
Energy Efficient - Compared to a conventional fluorescent lamp, it's up to 80 percent more efficient
Bright Solution - As much as 5 times brighter than traditional lights
High Endurance & Shock Resistant - LEDs have solid state components and are not fragile due to the absence of the filament and glass tube
Earth Friendly - It generates less CO2 because it consumes less power

LED Types

LEDs come in a huge variety and are available in different performance classes, various brightness levels, and package sizes, in the complete color range (including all shades of white), and in red, green, and blue.

LED products offer total solutions for illumination and lighting applications. Key products include high brightness and high power LEDs, PLCC surface-mount LEDs, and display backlighting module solutions. LEDs and display modules address a wide range of markets, including electronic signs and signals, automotive, solid state lighting, and LCD display backlighting.

High Brightness (HB) LEDs are specifically designed with small packages for space-limited applications such as display illumination. HB-LEDs offer long operating life and low power consumption and are well suited for many consumer and commercial lighting applications that have traditionally used conventional incandescent or other technologies.

Miniature

• Mostly single-die LEDs used as indicators, and they come in various-sizes from 2 mm to 8 mm, through-hole and surface mount packages

Mid-Range

• Medium power LEDs are often through-hole mounted and used when an output of a few lumen is needed. These LEDs are most commonly used in light panels, emergency lighting and automotive tail-lights. Due to the larger amount of metal in the LED, they are able to handle higher currents (around 100 mA). The higher current allows for the higher light output required for tail-lights and emergency lighting.

High Power (a.k.a. Solid-state lighting and LED lamp)

• High power LEDs (HPLED) can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for other LEDs. Since overheating is destructive, the HPLEDs must be mounted on a heat sink to allow for heat dissipation. If the heat from a HPLED is not removed, the device will fail in seconds. One HPLED can often replace an incandescent bulb in a torch, or be set in an array to form a powerful LED lamp.

Application Specific

• Flashing LEDs are used as attention seeking indicators without requiring external electronics.
• Bi-color LEDs are actually two different LEDs in one case. They consist of two dies connected to the same two leads antiparallel to each other. Current flow in one direction emits one color, and current in the opposite direction emits the other color. Alternating the two colors with sufficient frequency causes the appearance of a blended third color. For example, a red/green LED operated in this fashion will color blend to emit a yellow appearance.
• Tri-color LEDs are two LEDs in one case, but the two LEDs are connected to separate leads so that the two LEDs can be controlled independently and lit simultaneously. A three-lead arrangement is typical with one common lead (anode or cathode)
• RGB LEDs contain red, green and blue emitters, generally using a four-wire connection with one common lead (anode or cathode). These LEDs can have either common positive or common negative leads. Others however, have only two leads (positive and negative) and have a built in tiny electronic control unit
• Alphanumeric LED displays are available in seven-segment and starburst format. Seven-segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters. Seven-segment LED displays were in widespread use in the 1970s and 1980s, but rising use of liquid crystal displays, with their lower power needs and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.

LED Application Segments

• Lighting (General Illumination)
• Signage (including Traffic Signals)
• Display (LCD Backlighting)
• Automotive
• Amusement & Mobile Applications
  
• Flash