Last month, we described a simple linear supply for driving Lumileds' 1W Luxeon Star LEDs. Designed with low cost and simplicity in mind, it is ideal for experimentation as well as general-purpose fixed lighting applications.

The downside to this simplicity is that it's not very energy efficient. However, for portable and emergency lighting applications, efficiency is of paramount importance. In a low-efficiency lighting setup, much of the available energy is consumed by the power supply itself, where it's dissipated as heat.

Conversely, an efficient supply transfers the majority of the input power to the output, thereby maximising battery life.

This high-efficiency switchmode design can drive a single 1W Luxeon Star for more than 20 hours (continuous use) from a pair of alkaline "D" cells. It also includes a brightness control which, when set to the lower end of the scale, will extend useful battery life many times over.

The PC board is the same size as two "D" cells side-by-side, making it ideal for use in lanterns, emergency lights, beacons, etc. We envisage it being used anywhere that a portable, reliable and ultra-long-life light source is required.

It can drive green, cyan, blue and royal blue as well as white 1W LED varieties, most of which are available locally from the Alternative Technology Association (see panel).

Main Features High efficiency (>85%) Brightness control 2 x 'D' cell powered 20+ hours continous use Drives white, green & blue Stars