Not pitch black, but about 40-25 lux, comparable to a dim hotel room at night, according to one study. (Image above from RSNA News May 2007)
RSNA News May 2007 (p 13-14).
Viewing conditions for diagnostic images in three major Dublin hospitals: a comparison with WHO and CEC recommendations E Mccarthy, PC Brennan Br J Radiol, Vol. 76, No. 902. (1 February 2003), pp. 94-97. Link
Ambient Lighting: Effect of Illumination on Soft-Copy Viewing of Radiographs of the Wrist Patrick C Brennan, Mark Mcentee, Michael Evanoff, Peter Phillips, William T O'Connor, David J Manning Am. J. Roentgenol., Vol. 188, No. 2. (1 February 2007), pp. W177-180. Link
Here is brief motivational video by Dr Sumer Sethi, author of motivational book, Fire in the Belly In this video he talks about value of smaller victories ...