According to the measurements taken at the end of each
recording session,illumination level in the(covered)DARK treat-
ment was near zero lux(min and median:0lux,max: 1.0 lux),
while above the AMB treatment,the median value was 407 lux
(min :100 lux,max :940 lux).The median illumination level out side
the shelter was 635 lux while above the AMB experimental tubes it
was 560 lux on the final six mornings of the experiment.The shelter
thus caused some shading and experimental light levels did not
exactly correspond with natural conditions.The median relative