Surface-Mount Technology or SMT LEDs have no extending leads. Rather, they sit on the surface of the circuit board and are soldered so that the solder joint is on the top of the circuit board. SMT LEDs come in a wide range of sizes, varying from ultra-small 0.5 x 1.5 x 0.3mm LEDs to LEDs measuring 20 x 20 x 2.5mm or larger. Most SMT LEDs create a much more even illumination on the surface.