One of the biggest challenges a photographer faces when taking Infrared portraits is the “Dead Eyes” Because the eyes absorb light to create mental images, less is reflected back to the sensor, making the area of the eyes appear darker.
If you over exposure the image and the subject, you lose details in the image and the eyes are still dark. You can try and make adjustments in post production, but the results often look unreal.
My solution was a ring flash. A ring flash mounts on the front of the lens and is often used in portraits to give a stylized look to the reflection in the eyes.
Rather than use it as a flash, I turn the unit on so that the LEDs around the lens are illuminated. This floods the subjects eyes and face with light, shrinking the pupils and allowing my Infrared camera to capture eyes that have a more lifelike appearance.
Now we have eyes that can be lightened slightly and adjusted just like the rest of the image. From here, you can take a portrait in whatever direction you choose.