We have found these IR flashlights to be useful for testing eye tracking setups or even using them as permanent illuminators. They are very powerful (5W). Compact. And have variable focus.

940nm IR Flashlight Single Mode Zoomable Night Vision Light for Hunting

ABCLIGHT 850nm Infrared Flashlight 5W IR Light Single Mode with Adjustable Focus IPX54 Waterproof IR Flashlight for Hunting Night Observation

GaiGaiMall IR LED Illuminator Flashlight Zoomable 850nm Infrared Flashlight Night Vision Device for Hunting, Search& Rescue, Military Use.

They are powered by 3 AAA batteries. But that can be replaced by a 5V DC power adaptor such us :

Facmogu 2 Pack DC 5V 2A Power Adapter, AC 100-240V to DC 5V 2A 10W Power Supply Transformers, 5.5 x 2.5mm DC Jack Also Compatible with 5.5x2.1mm Socket

These cables are very helpful to build

MILAPEAK (Real 18AWG) 10 Pairs 12V 5A DC Power Pigtail Barrel Plug Connector Cable, 2.1mm x 5.5mm Male Female DC Pigtail Connectors for CCTV Security Camera and 12V Power Supply Adapter

The goal is to have an illuminator that can be plugged into a power outlet like this:

1. Drill a hole diagonally in the cap of the flashlight.

1. Pass the cable through the hole before soldering!

2. Solder the cable that goes to the power brick as shown in the picture. There are other ways, but this requires least modifications and keeps the functionality of the back button.

   

3. Push everything back together and close the cap