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How to Make an Infrared Floodlight

Something is nibbling at your garden every night, but every time you turn on the porch light, it dashes away before you can see it. If you make yourself an infrared (IR) floodlight, you can shine the invisible radiation into the garden and light up whatever is there, with the creature being none the wiser. There are dozens of ways to do this job depending upon your goals and constraints, but one example will serve to outline the process.

Things You'll Need

IR light-emitting diodes (LEDs)
Teflon or plastic disk
Cyanoacrylate glue or two-part epoxy
Drill
Resistor
12-volt power supply
Clamp-on reflector

Instructions

- 1
  Identify the key characteristics of your infrared source. As an example, you could select four 880-nanometer, 100-milliwatt, 50-degree viewing angle LEDs. The diodes have a voltage drop of 1.5 at a current of 20 milliamps. There are many other infrared sources you could select, such as a ceramic heater or a nichrome filament.
- 2
  Pick an electrically and thermally insulating mounting platform for the IR source. For the LEDs, this can be an 1/8-inch-thick piece of Teflon 2 inches in diameter.
- 3
  Attach your source to the mounting platform. For the LEDs of the example, drill four 5 mm holes through the Teflon, put a bead of glue around the mounting rim of the LEDs, and push them through the holes so the rim seats against the Teflon.
- 4
  Determine the electrical requirements for your specific source. The LEDs need 20 mA of DC current. With a 12-volt DC supply, they̵7;ll need a current-limiting resistor with a value of
  (voltage - 4 x (LED voltage drop))/current =
  (12 V - 4 x 1.5 V)/.02 = 300 Ohms.
- 5
  Attach your power supply to the infrared source. For the LEDs this means wiring one lead from the positive terminal of the power supply to the anode of one LED, connecting all the LEDs in series, then attaching one end of the 300-ohm resistor to the cathode of the final LED and completing the circuit by connecting the other lead of the resistor to the negative/common side of the power supply.
- 6
  Put your IR source in the bowl of the clamp-on reflector, routing the wires through the hole at the base of the bowl. For your LED assembly, you can glue the Teflon disk to the surface of the reflector bowl. The LEDs are directional beams, so the primary benefit to the reflector is as a convenient holder for your floodlight, but other sources will also use the reflector bowl to send infrared radiation in the right direction.

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