There are three main types of LEDs: miniature, alphanumeric, and illumination.

[edit] Miniature LEDs

These are mostly single-die LEDs used as indicators, and they come in various-size packages:

• surface mount
• 2 mm
• 3 mm (T1)
• 5 mm (T1³⁄₄)
• 10 mm
• Other sizes are also available, but less common.

Common package shapes:

• Round, dome top
• Round, flat top
• Rectangular, flat top (often seen in LED bar-graph displays)
• Triangular or square, flat top

The encapsulation may also be clear or semi opaque to improve contrast and viewing angle.

There are three main categories of miniature single die LEDs:

• Low current — typically rated for 2 mA at around 2 V (approximately 4 mW consumption).
• Standard — 20 mA LEDs at around 2 V (approximately 40 mW) for red, orange, yellow & green, and 20 mA at 4–5 V (approximately 100 mW) for blue, violet and white.
• Ultra-high output — 20 mA at approximately 2 V or 4–5 V, designed for viewing in direct sunlight.

[edit] Multi-color LEDs

A “bi-color LED” is actually two different LEDs in one case. It consists of two dies connected to the same two leads but in opposite directions. Current flow in one direction produces one color, and current in the other direction produces the another color. Alternating the two colors with sufficient frequency causes the appearance of a third color.

A “tri-color LED” is also 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.

RGB LEDs contain red, green and blue emitters, generally using a four-wire connection with one common (anode or cathode).

[edit] Five- and twelve-volt LEDs

These are miniature LEDs incorporating a series resistor, and may be connected directly to a 5 V or 12 V supply.

[edit] Flashing LEDs

These miniature LEDs flash when connected to 5 V or 12 V. Used as attention seeking indicators where it is desired to avoid the complexity of external electronics.

[edit] Alphanumeric LEDs

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 increasing use of liquid crystal displays, with their lower power consumption and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.

[edit] Lighting LEDs

LED lamps (also called LED bars or Illuminators) are usually clusters of LEDs in a suitable housing. They come in different shapes, among them the light bulb shape with a large E27 Edison screw and MR16 shape with a bi-pin base. Other models might have a small Edison E14 fitting, GU5.3 (Bipin cap) or GU10 (bayonet socket). This includes low-voltage (typically 12 V halogen-like) varieties and replacements for regular AC mains (120-240 V AC) lighting. Currently the latter are less widely available but this is changing rapidly.

Seoul Semiconductor Co., Ltd produces LEDs that can run directly from mains power without the need for a DC converter. For each half cycle part of the LED diode emits light and part is dark, and this is reversed during the next half cycle. Current efficiency is 80 lm/W.^[37]