Leaving the lights on for your dairy cows may be a good investment. Recent studies show that lighting in free stall barns can boost milk production by as much as 8 to 10%.

"Lighting can increase what's known as the 'photoperiod,'" said Bill Crist, Extension dairy specialist in the UK College of Agriculture. "The photoperiod is what governs a cow's internal biological clock. By lengthening this period, cows eat more feed and produce more milk."

Sixteen to 18 hours of light each day will give the best results. Sunlight works well, but artificial light can be used to extend the photoperiod. Crist said keeping lights on is a simple method that usually doesn't require additional labor. He said typical net returns can be 35 to 40 cents per cow, per day.

"High pressure sodium or metal halide lights are a good choice for unheated areas," said Larry Turner, Extension agricultural engineer. "In heated areas, flourescent lights can be used." Turner said the sodium light tends to be more yellow, while the halide light is more white. He suggested using a timer in combination with a photo sensor to provide the needed amount of light at the lowest cost.

"The timer allows current to reach the lights for 18 hours, such as 6 a.m. to midnight, then the photo sensor - located after the timer - activates the lights only when needed during darkness," Turner said.

A lighting level of 20 foot candles is generally recommended to ensure the desired effect. However, researchers have used as little as 10 foot candles of light intensity with positive results. Ten foot candles is about what a 100-watt bulb would produce in a 12 x 12 box stall.

Although extended lighting can improve milk production, Turner cautioned producers not to have too much of a good thing. "The 'off' time is still important," he said. "Cows still need to have darkness to help regulate their internal clock."

According to Turner, farmers can use low-level red lights for night vision during dark hours.

For more information on barn lighting, farmers can contact their local UK Cooperative Extension Service. Internet users may visit the UK agricultural engineering dairy facilities web site at http://www.bae.uky.edu/~lturner/dairyeng.htm.