Good lighting in combination with a good day / night rhythm in the cowshed is the basis for optimally performing cows.
Lighting and day / night rhythm influence milk production between 6 to 10%.
During farm visits I regularly see cowsheds that are too dimly lit (during the day).
In my opinion, the effect of light on the optimal functioning of cows is often underestimated in practice.
In addition to a day and night rhythm, cows need a certain light level to allow the day and night blocks to be physically fully operational. This mainly affects milk production. A well thought-out lighting scheme in combination with an optimal lighting plan reduces shadows in the cowshed. It also guarantees sufficient light during the day and a sufficient (dark) rest period.
With sufficient light on the retina of the eye, the secretion of the hormone melatonin is slowed down. The pituitary gland plays a guiding role in this. Melatonin induces sleep, increases body fat percentage and disrupts the cow's production capacity.
As soon as the melatonin level decreases, the hormone IGF-I is strengthened. The function of IGF-I is to increase activity in the animal, resulting in a higher milk production. That is why the right amount of light and a good day / night rhythm gives a higher milk production.
In winter, even with the available lighting, the required light level in cow sheds is often not achieved.
I consider a continuous light period of 16 hours and a light intensity of 180 Lux at animal level, followed by a dark period of 8 hours to be optimal.
During the summer period, the natural light level is normally sufficient.
Still, I am in favor of controlled lighting. Summer also has dark and cloudy days.