Presented in Figure 1 are the architectural details of two popular LED package designs. The conventional lead-frame hemispherical 5-millimeter LED featured in Figure 1(a) is commonly used as an indicator lamp for electronic appliances. Epoxy resins are used to cast the encapsulant system in these LEDs, which also feature cylindrical and rectangular lens geometries. The die is secured in a conical reflector cup that is soldered to the cathode lead and the anode is connected to the die with a bonding wire. Light emerging from the sides of the LED is reflected by the cup into the epoxy BODY. A flat cast into the base of the epoxy dome serves as an indicator of lead polarity. Typically, these indicator LEDs contain a die that measures 0.25 to 0.3 millimeters on the side, while the lens diameter ranges from 2 to 10 millimeters. The high-power GaInN flip chip diode cross section illustrated in Figure 1(b) is build on an aluminum or copper heat sink slug that can be soldered onto a printed circuit board for more efficient heat removal. Encapsulating the die is a protective silicone layer designed to overcome total internal reflection of emitted wavefronts and direct them through the larger plastic lens. A gold wire serves to connect the large cathode lead to the die, which is mounted on a silicon chip for protection against electrostatic discharge. The anode (not shown) is similar in configuration to the cathode, but projects away from the package in the opposite direction. LEDs of this design are currently the preferred choice for illumination in fluorescence microscopy.