Hands-free
Dimmable with three settings
Run times: 2-3 hours (high), 4-6 hours (medium), 20-30 hours (low)
Uses 3 AA batteries
Options for other LED colours

This hat lamp was inspired by ProdMod, who designed a 3W LED video camera light.

Step 1: Materials

3W Hat Lamp

3W White LED
10 or 30 degree LED lens with holder
Heatsink (2cm x 2cm)
2 pin connectors
Heat shrink tubing
Clear Epoxy

Battery Holder with Brightness Control

1 ohm 1/2 watt resistor
10 ohm 1/4 watt resistor
3 AA rechargeable batteries
On-off-on switch
4 AA battery holder (with cover and on-off switch)

Hat Lamp Holder

Hat
Velcro straps

Tools

Drill
Scissors
Dremel with grinding disc
Soldering iron
Hot melt glue gun
Alligator clips (to hold parts when setting the epoxy)

Step 2: Remove Extra Battery Contacts

Remove the contacts so that there is more space for the components. Use the last contact already soldered to a red wire to make this a three cell holder. The remaining slot is for the brightness control switch.

Step 3: Grind Battery Contact Holder

Step 4: Drill a Hole for the Switch and Wiring

Drill a hole for the brightness control switch. A hot soldering iron may be used to enlarge the hole. Warning: When heating the plastic, do this in a ventilated area.

Step 5: Convert 4 AA Holder to 3 AA Holder

Wire the holder as shown.

Step 6: Brightness Control Switch

This hat lamp uses two switches. The switch included with the battery holder is the power switch. The on-off-on switch combined with the built-in switch allows three different brightness settings.

If using red/yellow/IR LEDs, a 2-ohm resistor is required. It can be soldered to the LED externally if you plan on using different colours.

Brightness settings (for 3.8V 3W LEDs)
Direct drive - 1000mA
1 ohm - 500mA
10 ohm - 100mA

Note: The recommended forward current for 3W LEDs is 700 mA, but you can drive them a little higher. These LEDs usually have enough internal resistance for 3 AA batteries if you drive them directly. If using Luxeon Rebel and certain Cree emitters, you may need a minimum resistor value of 0.5 ohms for the high setting to limit the current to 1000 mA.

Step 7: Mount LED to Heatsink

Mount the LED to the heatsink. I used JB weld and clamped it with crocodile clips overnight, minimizing the space between the base plate and the heatsink. To provide strain relief for the wires, glue the wire to the heat sink

Step 8: Solder 2-Pin Connector to LED

2-pin connectors allow your lamp to be detachable, giving you the option to use other colours such as red for dark adaptation. You can also use it to select beam sizes.

Step 9: Test the Hat Lamp

Step 10: Attach Lens and Holder to LED

Grind the bottom of the lens holder to make room for the wires and solder joints. Attach the lens to holder and holder to LED using clear epoxy. Use epoxy sparingly along the rim of the lens and lens holder. Quick setting epoxy is preferred. Wipe off any excess epoxy with rubbing alcohol.

Step 11: Attach Light to Hat Using Velcro

Cut narrow openings for the velcro straps to go through. They will be used to hold the heatsink and battery holder. A small grinding disc may be used to cut the fabric. Make sure it is a hat you don't mind ruining. Hot melt glue may be used to keep the velcro from peeling.

If you prefer keeping the battery holder in your pocket, use longer wires.