Long-day lighting

Long-day lighting boosts milk production

There's an easier way to boost milk production than milking three times a day or using growth hormones: just leave the lights on longer, for 16 to 18 hours a day. The technique, long-day lighting, has been used successfully on poultry operations for years. Now, more and more dairy operations show increases in milk production and profits through long-day lighting — especially when energy-efficient lighting is used.

Milk production increased

Long-day lighting strengthens milk production and your bottom line. Studies have shown that long-day lighting can boost milk production from 5 to 16 percent.

Offsets low production in fall and winter

Milk production usually drops a bit during fall and winter because cows tend to eat less when it's dark. But extending lighting during the short-day seasons creates a stimulating effect, fooling cows' body clocks into thinking it's summer. More "daylight" results in more feed intake and more milk production. The key is keeping the feeding area consistently well-lit with either natural or artificial light for 16 to 18 hours a day.

Brightness and location of lights important

Research has determined the best types of lights, the optimum locations and the required brightness needed to boost milk production. Your WPS agricultural consultant can help you analyze the brightness and positioning of your current lighting system and can also calculate how much you'll save by installing energy-efficient lighting.

Sample floor plan of supplemental lighting program installation in stanchion or tie-stall barn. (Source: Stanisiewski, E. and H. A. Tucker, "Supplemental light increases milk yield in Michigan dairy herds." Cooperative Extension Service, Michigan State University, Bulletin E-2013, November 1986.)

Estimated profitability of long-day lighting1

  50 cows2 100 cows2 150 cows3 300 cows3
Annual profit per cow $62 $62 $62 $62
Total annual profit $3,100 $6,200 $10,050 $20,100

Source: Wisconsin Dairy Profitability and Safety Project, UW — Madison Biological Systems Engineering Department.

  1. After one-time start-up costs are paid off.
  2. Cows housed in tie-stall barn with fluorescent lamps.
  3. Cows housed in freestall barn with high-pressure sodium lamps.

Boost your bottom line further with energy efficiency

Most studies of long-day lighting involved fluorescent lighting rather than traditional incandescent lighting. Fluorescent lighting provides more light per energy dollar helps maximize profits.


Long-day lighting increases milk production, but may also result in higher costs for feed, electricity and lighting. But the increased milk yield produced by long-day lighting can actually cover these extra costs while leaving a net profit.

This University of Wisconsin study found that long-day lighting results in a daily profit of 34 cents per cow during the long-day lighting season.


The payback period for long-day lighting varies from operation to operation. The installation costs depend on the following:

  • barn style
  • current lights being used
  • number and capacity of lamps
  • mounting height
  • fixture spacing

WPS estimates the one-time lighting and installation costs are $36 to $54 per cow, or 20 to 30 cents per cow per day for the first season that long-day lighting is implemented. A recent study by the University of Maryland derived returns of 30 to 45 cents per cow per day, while a University of Wisconsin study (see table above) found a daily return of 34 cents per cow. A likely profit scenario follows: With a return of 34 cents per cow per day, a $45-per-cow investment in lighting would be recovered in 132 days. If you install a completely new lighting system with energy-efficient fixtures, the project could break even in one fall/winter season.