Table 1. Ambient light sources and corresponding symbols, used in Fig. 7.

○	No lights	⬜	Surgical light low direct
+	LCD monitors	◇	Surgical light low indirect
$\ast$	IR source - Neuronavigation	△	Surgical light high indirect
▷	Microscope light	▽	Fluorescent lights
x	Surgical light high direct	◁	External light