(a)
The instrument lights must—
(1)
Provide sufficient illumination to make each instrument, switch and other device necessary for safe operation easily readable unless sufficient illumination is available from another source; and
(2)
Be installed so that—
(i)
Their direct rays are shielded from the pilot's eyes; and
(ii)
No objectionable reflections are visible to the pilot.
(b)
Unless undimmed instrument lights are satisfactory under each expected flight condition, there must be a means to control the intensity of illumination.
Code of Federal Regulations
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-72, 55 FR 29785, July 20, 1990]