Hens under red light from wk 19 to 22 showed significantly better early laying performance (70.6%) than with white or green light (52.0 and 40.4%, respectively).
This favorable effect of red light on egg production is known (Pyrzak et al., 1987) and is confirmed by our results and Gongruttananun (2011) who reported that native Thai-pullets (Gallus domesticus) under constant red LED lighting (16 h) had higher laying performance in the first 8 wk compared with hens under pure daylight (12 h) supplemented with white fluorescent (4 h) or red LED light (4 h). He also observed a significantly earlier onset of lay, which corresponds with the trend observed in this trial. Mobarkey et al. (2010) showed convincingly that these effects are due to the sensitivity of the hypothalamic extra-retinal photoreceptors to long-wave radiation and not to a reception through the retina. Light intensity was not found to have an effect on the onset of lay (Renema et al., 2001).