It is not hard for an LED lighting design to be more efficient than High Pressure Sodium or Fluorescent lighting, but most LED lighting on the market today is not as efficient as it could be. In the world of HPS and Metal Halide lighting, the energy bandits are the ballast and the bulb itself, each wasting power in the form of heat. Commercial LED lighting has its own energy bandits to deal with, first and foremost of these is the power supply. The best switching power supplies are only 90 to 95 percent efficient, lower quality supplies may be 80 percent efficient or less. Much of this loss is due to heat, but some is simply due to losses in the circuitry; the unavoidable consequence of an overly complicated design. LED lighting designs that use a external power pack can hope for about 70 percent efficiency at best from their power supply; that's before you even get to the light itself and its power gobbling resistors.
So how do you minimize the losses? By simplifying the circuitry and eliminating the energy bandits.
Build A Sun modules plug directly into any standard US 120 VAC outlet. There is no transformer because the device is designed to utilize the full voltage available, instead of having the voltage adapted to fit the needs of a low voltage DC circuit, as most commercial designs do.
LEDs typically run on around 3.5 volts dc, and it is common for manufacturers to string them together in series groups of three along with a resistor to allow them to be operated at 12 volts dc. Each group of three LEDs needs a resistor to limit the current and "eat up" the extra 1.5 volt difference between what the LEDs need and what the 12 volt supply provides. Several of these groups are connected in parallel to form light panels powered by 12 volts dc, which then need a 12 volt dc power supply to feed them.
Build A Sun modules contain a single fixed resistor, used for calibration measurements, and a variable resistor to adjust the current to the proper level. These are essentially the only losses between the power from your wall and the LEDs themselves. No complex or wasteful power supply, just power straight to the LEDs; 2.5 Watts to be exact.
The choice of LEDs is important when talking efficiency. Many people are confused by the sea of numbers associated with LED stats. Wattage rating generally refers to the power consumption of a light, but many equate it to the actual light output. Light output is further confused by the way manufacturers rate their products. Light fixture and bulb manufacturers tend to express light output in Lumens, which unfortunately cannot be verified by consumers without special equipment and/or calculations; it is simply a relatively arbitrary number, thrown out for consumers to make comparisons with. LED manufacturers tend to express output in millicandella; but this measure references to the light output of a candle, and most of us don't have much familiarity with candles any more. Common light meter apps available for smart phones measure output in Lux; and while this is again a somewhat ambiguous number to the average person, it is verifiable through free smart phone apps and therefore the measurement used on this site for stating the output of Build A Sun modules.
LEDs are made in so many styles, colors and sizes that the choices are easily overwhelming. There are standard LED types in 3mm, 5mm, 8mm, and 10mm; there are strip LEDs, COB LEDs, 1W, 3W and 5W LEDs; there are OLEDs and Piranha LEDs and new types and styles every month.
After wading through it all, the Piranha comes out on top here at Build A Sun. Designed for signage, they need to be bright, tough, and efficient. Many other LED forms run at a much higher current level, but the light output is not proportionally higher for the extra power cost; meaning reduced efficiency overall and more heat generated.