An LED is a light source made from semiconductor materials

An LED is a light source comprised of a small chip covered with transparent resin. The chip is composed of semiconductor materials, and emits light at the junction/connection area between the materials when current flows through. A semiconductor possesses a conductivity intermediate between a conductors and insulator. When a p-type semiconductor and n-type semiconductor are placed together and voltage is supplied, current flows through the movement of electrons/holes. When an electron meets a hole, it falls into a lower energy state and releases energy, in the form of light (photon).

The emitted color of an LED is determined by the constituent elements

The types of materials that comprise the LED determine the color within a specific range, based on the resulting energy (band) gap. A wider gap will create shorter wavelengths while a smaller bandgap will produce longer wavelengths. For example, in the diagram below we can see that for an AlGaInP system the emitted color can range from yellow to red and beyond.

Light is a component of electromagnetic radiation

Visible light is a part of the electromagnetic spectrum, situated between ultraviolet and infrared rays, and is perceived as color.

Two types of LEDs

LEDs are available in 2 basic types, a surface mount chip type and a leaded (through-hole) lamp style. Select the ideal solution based on intensity/brightness, directivity, and mounting constraints.

The main component is an ultra-compact chip on the order or microns

LED chips are made from a wafer base consisting of SiC (Silicon Carbide) and Al2O3 (Sapphire). This LED element is enclosed with resin together with a bonding wire and electrode.

There are 3 main ways to make a white LED

(1) Red LED + Green LED + Blue LED

White light can be emitted using an RGB LED. These units are also currently used in full-color displays since the red, green and blue elements can be used to make a wide range of colors.

(2) Near-Ultraviolet LED + Red/Green/Blue Fluorescence

This method uses a near-ultraviolet LED with a short wavelength similar to blue. The three different wavelengths of light resulting from the red, green, and blue phosphorescence creates white light with good color rendering properties.

(3) Blue LED + Yellow Phosphorescence

This method is the most widely used for lighting. A blue LED and yellow fluorescence are used to make white light, with red and green fluorescence added to maintain color rendering characteristics.
Topic 12

It is not possible to make white LEDs without flourescence

The fluorescent substances are extremely small particles that, when exposed to certain wavelengths, emits visible light. Yellow, green, and red fluorescence are added with a blue or near-ultraviolet LED to emit white light.
Two techniques are used to combine the blue LED and fluorescence:
1) The fluorescence is mixed with the resin and encloses the blue LED
2) The fluorescence is placed directly on the chip itself

20 million times faster response speed than incandescent bulbs

LEDs provide excellent responsiveness, making them ideal for stop lamps in cars that require instantaneous response. LEDs feature a response of 100ns or less, compared to incandescent light bulbs that require anywhere from 0.15 to 0.25 seconds to reach the specified light intensity.