Time of lay in hens exposed to intermittent lighting.

1. Two short-term trials are described in which laying hens were exposed to 8 h light followed by 8 one-min pulses of light at hourly intervals followed by 8 h darkness (8L:8i:8D). The effect of varying the intensity of illumination during the one-min pulses and the effect of placing the intermittent lighting before the 8 h photoperiod (8i:8L:8D), were studied. 2. Normal egg production was maintained by the 8L:8i:8D system when the light pulses were at 20 lux, but not at 5 lux. This suggests a minimum threshold for illumination with short light pulses higher than that needed for continuous lighting. 3. Time of lay under 8L:8i:8D was the same as with 8L:16D in relation to the beginning and ending of the 8 h main photoperiod, but with 8i:8L:8D mean time of lay was 2 to 3 h earlier. Thus the hourly pulses caused a phase advance when placed before the normal photoperiod but did not cause a phase delay when placed after the normal photoperiod.