SMD stands for Surface Mounted Device and offers a number of advantages over their standard 'through-hole' counterparts. As the name suggests, an SMD is a type of LED that is mounted and soldered flat against a surface.
i) More energy efficient / powerful:
Firstly, SMDs offer a much better lumen to watt ratio (lm/W) than regular LEDs. This means they are cheaper to use and create more light for an equivalent amount of power. A 4 watt SMD bulb is capable of generating up to 350 lumens of light, which is about equivalent to a 60 watt halogen bulb. Even a 2 watt SMD bulb can manage 190 lumens; about the same as a 35 watt halogen.
ii) Wider beam angle:
Secondly, SMDs offer a much wider beam angle. One of the defining characteristics of LEDs is their directional light source. Most LEDs feature an epoxy enclosure that closes down the angle of light. With an SMD this enclosure is completely removed (the diode is exposed to the air) allowing the diode to distribute its light over a much wider area. An SMD by itself will emit light at an angle of 120 degrees.
The biggest advantage here is that manufacturers are able to develop bulbs for very specific applications by reintroducing optical lenses. The latest development in LED technology are 60 degree SMDs, which are perfect for general purpose lighting.
iii) Longer Life Expectancy:
SMDs generally last longer than older LED formats. This can be anything up to 50,000 hours, which is many times longer than an incandescent, and about twice, to three times as long as a compact fluorescent lamp (CFL). This virtually removes the maintenance cost and significantly lowers the replacement cost.
iv) Smaller / more compact:
Perhaps the biggest advantage offered by SMDs relates to their size. Standard LEDs come as packages. In addition to the diode (the actual light emitter) they also feature optical lenses and wire connectors, which take up a surprising amount of space.
With an SMD, this is all removed, leaving just the diode. This allows manufacturers of LED bulbs to make their bulbs to much smaller specifications, thereby improving their versatility.
An added benefit of SMDs, one that few people tend to realise, is that they are also easier and cheaper to produce. This is because they lend themselves much better to automated assembly.
In summary, SMDs are a vital development in terms of LED technology and will help LEDs secure a much greater portion of the global lighting market in the near future by offering consumers an option that is potentially much cheaper.