A light ratio of 2:1 hitting participants' faces vs the background directly behind their face is desirable.
Average vertical illumination on participants' faces should be around 400 lux. Avoid levels any higher than 500 lux on people's faces and ensure luminaires are low glare.
Good visual comfort and uniformity is paramount, below are some general guide parameters:
Target uniformity ~0.6Uo
Colour temperature ~4500 kelvin.
Colour rendering index (CRI) ~80+
Key Hints
Lighting level on the working plane should still be within CIBSE guidelines.