The picture to the left shows the configuration of a standard light diode. The chip is embedded in a reflecting tub. The right picture shows the reflector after the removal of the transparent plastic coating. The rectangular wire supporting the reflector, establishes the contact to the cathode and absorbs the lost heat. In the centre of the chip you can see part of the bond wire, which establishes the contact to the anode.

On the picture to the left the bond wire is shown as a horizontal line on the right side above the carrier. The cathode (-) is marked by a bevel at the left of the housing socket. The cathode connection of brand-new LEDs is shorter (standard rule: cathode = short). In most of the LEDs the reflector is the cathode, there is also a standard rule: the technical current direction is “indicated” by the arrow built by the electrode’s form (see picture to the right). Attention: in rare cases the configuration is just the other way round ! High-power LEDs are operated with higher power. This requires a higher performance in the heat elimination, expressed in specific construction types. The heat can either be carried off via the feeders, or the power is supplied via two bond wires and the heat is eliminated through a separated reflecting tub. The industrial processing of THD (through-hole-device) LEDs is complex and expensive. LEDs are therefore also produced in SMD (surface-mounted-device) housings.




An additional possibility is the direct “bonding” of the LED chip on a circular board (chip on board – COB). Multicolor light diodes consist of  several (2 or 3) diodes in one housing. The version with 2 connections has 2  LEDs in opposite directions connected in parallel. Depending on the polarity the one or the other diode is emitting light. An alternating voltage excites both diodes and produces an overlapping color.