The end of daylight savings and no lights meant that 5:30 pm soccer practice would be totally dark. With field space severely limited this meant the end of practices. Next year we will be ready with portable battery powered field lighting, thanks to low cost, high power LEDs and lightweight long lasting lithium 36 volt battery packs from Dewalt.

I built two stadium lights. Placed on opposite sides of the field they do a nice job of lighting a decent size practice area for 10-12 kids. For a larger field or different sport, you may need several more. Each light draws ~.750 Amps, the Dewalt pack is good for 2.3 Amphours or not quite 3 hours. Still more than long enough for practice.

Needed 36 Volt Dewalt Lithium battery pack
These things are great, lightweight, fast charging, and very convenient after you have followed the directions to add standard power out wires. I will not detail how to disassemble the battery as this is readily available on the internet in several places.
http://www.slkelectronics.com/DeWalt/packs.htm
http://www.youtube.com/watch?v=qQJUEeKo7KQ
9 STAR LEDs (3 watts ~100 lumen each now available direct from China for around $2 per LED, ebay and other sources)
Most of these high power, high efficiency LEDs operate from 3.5 to 4.0 Volts. To save money we are not going to use the recommended constant current driver, but wire directly in series. (36 V / 9 LEDs) = 4.0 volts per LED.
CPU style heat sink
1 ohm, 10 watt resister (to add some safety margin)
18 inch long piece of aluminum angle (1/16" by 1 inch)
JB Weld Epoxy
1 inch hose clamp
10' x 1/2 pole (PVC pipe)
Screws, wire, solder

Step 1: Solder Leads to the Star LEDs

STAR LEDs are very nice to solder. They have wide solder pads, clearly marked + and -. Start with the plus side and solder one lead to one + pad.

Step 2: Continue Soldering All 9 LEDs and 1 Ohm Resister in Series

Solder your leds into a series circuit. The first wire goes to the + pad on the first LED. Solder the second wire to the - pad of the first LED and solder this same wire to the + pad of the second LED. The next wire goes from the - pad to the + pad of the third LED. Continue until all 9 LEDs are soldered in the string you see below. Next solder one terminal of the 1 ohm resister to the last wire and solder two 10' lead (+ and -) wires to the ends.

Step 3: Epoxy the STAR LEDs to the 18 Inch Aluminum Angle

3 watt LEDS at full power may generate enough heat to eventually destroy themselves unless applied to a heat sink. You could buy special thermal epoxy but JB Weld brand epoxy appears to have enough metal to bond the LEDs and work as transfer heat. Bond all your LEDs to the aluminum and clamp firmly in place for several hours.

Step 4: Add Heat Sink, Hose Clamp and Test Your Lights

With the LEDs on the aluminum angle will become quite warm. Adding a heat sink (from a CPU cooler) is a good idea to maintain efficiency and LED life. Bolt on a hose clamp for mounting your lights to a tall pole. Plug in and test your lights.