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Take Home Messages

Cows allowed 16 to 18 hours total day length at  20 to 30 foot-candles at eye level daily during winter increases milk yield by 5-16 %.  

Continuous light is not recommended - there should be a 6-8hr break - and approx 8 hrs supplemental

Automate switch on for Metal Halide or High Pressure Reflector / Refractor Units to ensure sufficient exposure.  These lamps last 20-28,000 hours = a minimum 14 year depreciation.

Dry cows should never be exposed to long day length during the winter.

Download the Zipped Excel File to calculate lighting need

Stephen Bettany at the  farmenergy.com provides design and materials sourcing at  120 per shed.


Original work by Michigan State University showed long winter Photoperiods of 16 hours light: 8 Hours of dark increased milk yield 5 to 16% (4,5). These observations were Confirmed and extended by numerous other researchers in the last 20 years. Across 10 different studies using long day photoperiods, milk production increased an average of 2kg  per cow per day (1).


16 to 18 hours of total light per day increases milk yield. 
Continuous light is not recommended because the cows interpret this as a short day. 
In other words, a cow needs 6 to 8 hours of darkness within each 24hour period to achieve the optimal increase in milk production to a lighting system. To accomplish 16 to 18 hour photoperiods, the lights should be controlled with an automatic timer. Don't rely on your memory or that of others to turn lights on and off manually. Provided sunlight can readily penetrate the facility, it is possible to supplement with artificial light for relatively short intervals before sunrise and after sunset. Such a supplemental scheme will save on operational costs. The principle is to provide a total of 16 to 18 hours of light each day.

Long day induced increases in milk yield occur when intensity of light is at 20 to 30 foot-candles at eye level of the cow. Intensity of light can be measured with a handheld light meter. Lamps should be placed over the cows' heads where they spend the most time. Therefore, the cubicles, not the feed passage, should be the primary area lighted. "Head to head" rows of cubicles can be lighted with a single row of lamps. The feed passage may be lighted, but this involves increased costs of installation and operation of additional lamps. It is not necessary to have 20 to 30 foot-candles of light in every nook and cranny of the facility. Remember, as height of the lamps above the cows' heads increases, a greater area is lit, but intensity of light decreases. Periodically cleaning lamps is essential to maintaining intensity of light.

Fluorescent lamps are recommended only for houses with low ceilings such as found in many kennels. In cold houses the fluorescent fixture should be equipped with a high output, rapid start, dust and moisture resistant, -20 degree Fahrenheit ballast.
Metal halide / High Pressure Sodium lamps are recommended for houses with high ceilings such as usually found in cubicle house.
Though more expensive, lamps equipped with a reflector and refractor are more energy efficient.

Lights and bST
Long day photoperiods combined with bST additively increased milk production (2). Increased milk production occurs within a few days after bST treatments are initiated; whereas long day induced increases in milk yield require several weeks of exposure. In confirmation of Michigan's earlier work, long day photoperiods increased dry matter intake in these more recent studies. Indeed, long day photoperiods may stimulate feed intake earlier in cows treated with bST as compared with bST alone.

Lights and 3X milking
There have been no reports comparing light induced and 3X milking induced increases in milk yield, although there is no apparent reason to believe that milk yield would not increase, at least additively, to a combination of both management practices. A troublesome problem with a combination of long days and 3X milking is supplying a sufficient number of hours of darkness. One approach may be to offset the lighting schemes in separate pens so that different pens receive darkness at different times of the day. Coordinate exposure to lights with routine feeding, management, and milking practices. Placement of 4 Watt red incandescent lamps 20 to 30 feet apart along walkways can be used to assist with movement of cattle in the dark.

Lights and the Dry Period
Surprisingly, new research shows that exposure to long day photoperiods during the dry period reduces milk yield in the subsequent lactation by more than 5L  per day in comparison with cows given short day photoperiods (8 hours of light: 16 hours of dark) (3). Perhaps cows eventually become refractory to continuous exposure to long days in the previous lactation, and exposure to short days during the dry period resets a cow's responsiveness to the stimulatory effects of long days during the subsequent lactation. Depending upon accommodation, the dry period would be an ideal time to expose dairy cows to short day photoperiods in order to stimulate subsequent milk production.

1. Dahl, G.E., et al. 2000. J. Dairy Sci. 83: In Press.
2. Miller, A.R.E., et al. 1999. J. Dairy Sci. 82: In Press.
3. Miller, A.R.E., et. al. 2000. J. Dairy Sci. 83: In Press.
4. Peters, R.R., et al. 1978. Science, 199:911.
5. Peters, R.R., et al. 1981. J. Dairy Sci. 64:1671.
6. Michigan Dairy Review, Vol. 2: 7, February 1997.
7. Michigan Dairy Review, Vol. 5: 1, January 2000

Acknowledgement:  Adapted from the Michigan Dairy Review