Dairy lighting system for free stall barns and milking centers

Proper lighting in a milking center and the housing area will add to a high quality working environment to improve worker efficiency, safety, and comfort. Provision for the right amount of light may improve the productivity of dairy workers. Research trials indicate that supplementing lactating cows with 16 to 18 hours of light per day increases milk production by 5 to 16% as compared to cows exposed to 13.5 hours or less of light per day (Peters, 1994). The purpose of this article is to provide the dairy producer with enough information to design or evaluate the lighting in their facility. The article is arranged using a step by step design procedure with background information and design tables. At the end are examples of dairy lighting for a milking center and free stall barn.

Summarized by Milkproduction.com staff from: AEU-12, University of Minnesota, U.S. Department of Agriculture, and Minnesota Counties Cooperating

Unit Conversion:
1 lux = 0.09290304 foot-candle and 1 foot-candle = 10.76391 lux

The purpose of this article is to provide the dairy producer with enough information to design or evaluate the lighting in their facility. This Update is arranged using a step by step design procedure with background information and design tables. At the end are examples of dairy lighting for a milking center and free stall barn.

Design process

The design process consists of three steps:

  1. Determine the illumination level required for a given area or task.
  2. Select the type of lamp which would be best suited for that area.
  3. Determine the size of lamp and spacing between lamps needed.


The rate of flow of light from a source such as a lamp or the sun is measured in lumens. Illumination is the amount of light striking the surface at some given distance from the light source. The unit of illumination in the English system is the footcandle (fc). In the metric system illumination is measured in lux (lumen per square meter). One footcandle is equal to about 10 lux.

Illumination levels for various areas in a milking center and a free stall barn are in Table 1.

Table 1 Recommended illumination levels for the milking center
Work Area or Task Illumination Level
Parlor Room  
General Lighting
Operator's Pit
Milk Room  
General Lighting
Washing Area
Bulk Tank Interior
Loading Platform 20
Utility or Equipment Room
Holding Area
Treatment and Maternity Areas  
General Lighting
Treatment or Surgery
Feeding Area--Free Stall Barn

In dairy housing barns the lighting requirements to stimulate additional feeding activity that results in increased milk production must provide the following: (1) 10 to 20 footcandles of illumination in the feeding area of the barn, (2) a 16 to 18 hour time period at the above level of light, and (3) a continuous dark period of 6 to 8 hours. Providing illumination for 24 hours a day does not yield any additional production or animal health benefits.


Types of lamps that are available for lighting include: incandescent, fluorescent, halogen, high-pressure sodium, and metal halide. Because of their efficiency, fluorescent lamps are recommended for most areas of the milking center, although metal halide work well in large parlors with high ceilings. High-pressure sodium lamps are recommended for free stall barns with high ceilings and for milking center holding areas. The most important characteristics for each type of lamp are listed in Table 2 and below.

Lamp Efficiency.
The efficiency of a lamp is expressed as the amount of light provided per unit of input energy, or lumens per watt. Lamp efficiency usually increases with lamp size.

Lamp Life.
Lamp life is the time a lamp operates at its designed level. The more energy efficient lamps also have the longest useful life.

Starting Temperature.
Starting temperature is generally only important when selecting a lighting system for a cold environment. Incandescent and high-pressure sodium lamps perform well at cold temperatures (-20° F). The minimum starting temperature for most fluorescent lamps is 50° F, except those equipped with cold starting ballast.

Warm-up period.
Incandescent and halogen lamps do not have a warm-up period. Fluorescent lamps have a slight starting delay, but it is not significant. All of the high intensity discharge lamps have a significant warm-up period which can range from 1 to 15 minutes.

The color, or degree of whiteness, of a light source is defined by the color rendition index (CRI). A CRI of 80 or more is required for color matching tasks.

Table 2 General characteristics of common light sources
Lamp Type Lamp Size (Watt) Color Rendition Index Efficiency (Lumens per Watt) Lamp Life (Hours)
60-200 100 15-20 750-1000
50-150 100 18-25 2,000-3,000
32-95 70-95 81-98 15,000-20,000
High Intensity Discharge:        
Mercury Vapor
50-250 20-60 40-50 16,000-24,000
Metal Halide
100-250 60-80 80-92 7,500-10,000
100-400 20-80 90-110 15,000-24,000

Light quality in a work area must be considered in addition to quantity and efficiency. Lighting quality is not only influenced by color of the light source but also by the light uniformity, spacing, glare, and reflectance of the surfaces in the room.

Glare is the result of excess light that is in the normal line of sight in the work area. Glare is defined as any brightness in the field of vision that causes discomfort, reduction in vision, or eye fatigue (ASAE, 1993). The light can be emitted directly from the fixture or be reflected from a glossy surface. Positioning of the fixtures and the reflectivity of the surfaces in the room influence the amount of glare. Mount fixtures above the line of sight to reduce glare.

There are two basic designs for high-intensity discharge lamps that meet code requirements for dairy buildings (Figure 1). Fixtures that include a reflector behind the lamp and a diffusing lens tend to project a greater portion of the light downward. The second fixture option has only a diffusing lens and tends to emit light in a wider pattern.


Refractor and Reflector Type       Refractor Type Only

Figure 1. Fixture option for High-Intensity discharge lamps.


Once the illumination level and type of lamp have been determined, the next step is to determine the area each fixture will illuminate. This section contains a set of design tables to assist in designing the lighting system. These tables were developed based on lamp data from several manufacturers, in-service performance data of Chastain (1994), the design methods described by MacDonald and Henderson (1991), and Frier (1987). Use tables to determine the floor area each fixture will illuminate based on knowing mounting height and type of lamp. This step is divided between the milking center and where the cows are housed.

Table 3 Floor area per fixture (ft2/fixture) needed for general area lighting using fluorescent lamps (T8 only)*

Table 3a. Floor area per fixture to provide 10 fc of illumination.

 Length = 4 ft Lamp Length = 8 ft
Height Above Floor, ft
2 lamps
4 lamps
2 lamps
2 lamps
203 406 344 575
174 348 295 493
140 280 236 395
116 232 196 329
100 200 168 282
87 174 147 247


Table 3b. Floor area per fixture to provide 20 fc of illumination.
   Length = 4 ft  Lamp Length = 8 ft  
 Height Above Floor, ft
2 lamps
4 lamps
2 lamps
2 lamps
 102  204  172 288
 87  174 147 
 70  140 118 
 58   116  98 164
 50  100  84 141
 44  88 74 


 Table 3c. Floor area per fixutre to provide 50 fc of illumination.    
Length = 4 ft
 Lamp Length = 8 ft    
Height Above Floor, ft
2 lamps
4 lamps
2 lamps  
2 lamps
 40  80  67 113
 35  70 59 
 28  56 47 
 23  46 39 
 20  40  34  56
 * Work area was assumed to be 2 feet above the floor.    

Lighting design for the milking center
General lighting areas

Many areas of the milking center require illumination levels of 10, 20, or 50 footcandles (from Table 1). Fluorescent lamps are recommended for all of these areas. Table 3 shows the design values for fluorescent fixtures. Use this table to determine the floor area per fixture for a given illumination level, mounting height, and lamp size.

The ratio of the fixture spacing to the mounting height determines the uniformity of light in a work area. A high level of uniformity is required in an intense work area such as a parlor pit, office, and milk room washing area. This level can be achieved by using a fixture spacing to mounting height ratio of one. For example, space the fixtures 8 ft apart or less if the mounting height is 8 ft. A spacing to mounting height ratio of 1.8 or less is adequate in other areas of the milking center. Highly reflective wall, ceiling, and floor surfaces will enhance the uniformity of illumination.

Parlor pit

Since the parlor pit is an important work area, it should be illuminated to 50 fc. The majority of fluorescent fixtures that are watertight have only a refractor. Fixtures with only a refractor work well for general area lighting applications, but do not project a significant portion of the light straight down. Therefore, the amount of light emitted from the fixture that can be utilized at task level decreases significantly as mounting height increases. Fluorescent fixtures must be suspended 7 to 10 feet above the pit floor to provide 50 fc of high quality illumination. Since in modern parallel and rapid-exit herringbone milking parlors the ceiling height above the pit floor can range from 12 to 16 feet, the fixtures must be suspended from the ceiling.

Table 5 Floor area per fixture (ft2/fixture) needed for parlor lighting using metal halide lamps*.

Illumination Level   Lamp Size  
fc 100W* 175W** 250W**
135 243 369
54  97 148

* Low bay fixtures are avaiable that allow a 100 W metal halide lamp to be used from mounting heights from 10-20 feet.
** Low bay fixtures are available that allow a 175-250 W lamp to be used from mounting heights from 12-20 feet.

In large, naturally ventilated parlors with high ceilings, metal halide lamps with a CRI of 80 to 92 can be used. Table 5 provides design values for metal halide lamps for 20 and 50 fc of illumination. Low-bay fixtures (fixtures that are designed for mounting heights under 20 feet) with both a reflector and a refractor are required. Use only totally enclosed fixtures since they may burst and ignite a fire in the parlor. Select a fixture with a refractor that is designed to contain all glass fragments. Select a lamp that will provide 50 fc in the pit and results in a spacing to mounting height ratio near one to provide uniform light distribution.

Holding area

In cold climates, like Minnesota, high-pressure sodium lighting is recommended for use in the holding areas; but fluorescent lamps with cold starting ballasts may also be used. Special low-bay high-pressure sodium fixtures are available that can be used with 100 watt lamps at mounting heights as low as 10 feet. Most holding areas can be illuminated well with 100 or 150 watt lamps. Only use 250 watt lamps for holding areas that require mounting heights of 16 feet or more to provide adequate light uniformity. Table 6 specifies design information for lighting the holding area with high-pressure sodium lamps.

Table 6 Floor area per fixture (ft2/fixture) needed for holding and treatment area lighting (10 fc) using high-pressure sodium lamps.

Refractor Only Reflector and Refractor
Height Above Floor (ft) 100W 150W 250W 100W 150W 250W
304     390    
  512 880   656 1128

Bulk tank inspection and veterinary treatment

Table 1 indicates that bulk tank inspection and veterinary treatment require 100 footcandles of illumination. These tasks also require the highest color rendition (CRI = 100). Lighting for these areas is best provided by directing light toward the work area using halogen spot or flood lamps. Two or more spot or flood lamps may be needed to provide adequate lighting for veterinary treatment. Adjustable ceiling or wall mounted fixtures will allow the light to be aimed where it is needed. Halogen lamps provide the best combination of lamp life, color rendition and efficiency (Table 2).

Halogen flood and spot lamps provide an inexpensive way to provide the required illumination in these work areas since they are relatively small. The lighting level provided by spot or flood lamps is often rated in terms of candlepower and not lumens. The illumination level in footcandles can be estimated from the rated candlepower of the lamp and the distance from the lamp to the work area. Table 7 gives the required information to select halogen lamps to provide 100 footcandles of illumination at distances from 42 to 190 inches.

Use a single narrow spot or spot lamp for bulk tank inspection that is mounted to the side of the inspection port of the bulk tank. Mounting the lamp to the side will prevent pieces of a broken lamp from falling into the bulk tank. Use a ceiling mounted fixture that allows the beam of light to be aimed into the bulk tank.

Supplemental lighting design for lactating cows

Ten to twenty footcandles of illumination in the barn is required. Research studies have shown that an illumination level of 10 footcandles is sufficient for photo period control (as reviewed by Peters, 1994). As a result, this is the minimum light level that should be used for lighting design for the feeding area. However, in areas where cows may be restrained for breeding or minor treatment, the lighting system should be designed to provide 20 footcandles.

Table 7 Selection of halogen spot and flood lamps for bulk tank inspection and veterinary treatment.

Maximum Distance From Task to Provide 100f of Illumination (inches)*.
Lamp Size, W
Candlepower Narrow Spot Spot Flood
50 8,050



* Estimates based on: fc=cd/d2, where cd=candlepower, and d=distance from lamp to work area (ft) (Frier, 1987).

In free stall facilities cows are often bred while restrained in a self-locking stanchion at the feeding fence or in a near-by stall. Therefore, the recommended illumination for the feeding area in a naturally ventilated free stall barn is 20 footcandles. High-pressure sodium lamps are mounted above the feeding fence in cold free stall buildings. Since naturally ventilated free stall barns have ample amounts of natural light during mid-day, a timer should be used to control the lighting system for early morning, late evening and night time hours. For example, turn the lights on at 4:30 A.M., off at 9:00 A.M., on again at 4:30 P.M., and off at 9:30 P.M. Select the exact lighting schedule based on the milking schedule. The key is to make sure that the combination of natural and artificial illumination results in a continuous lighting period of at least 16 hours. During the summer months the lighting system may only be needed to supplement natural light during the morning and evening milking.

Lighting design values for both 10 and 20 footcandles are shown in Table 8. The spacing of the fixtures determines how uniform the light will be in the feeding area. Fixture spacing, measured from center to center of each fixture, is expressed as the ratio of the fixture spacing to the mounting height. In the feeding area a fixture spacing ratio of 1.8 or less is sufficient. Therefore, the maximum fixture spacing that should be used for a barn with an 8 foot ceiling is 14.4 feet (8 x 1.8)


Table 8 Floor area per fixture (ft2/fixture) needed for supplemental area lighting (10 & 20 fc) for lactating cows.

Lamp Type Lamp Size Floor Area Per
10fc (ft2)
Fixture to Provide
20fc (ft2)
100W 52 26
32W (1 lamp)
32W (2 lamps)
High Pressure Sodium (Reflector + Refractor) 150**
High Pressure Sodium 150**
* Mounting height is 8 ft above the manger surface.
** Mounting height is 10 to 15 ft above the floor.
***Only use 400 watt lamps if mounting height is 15 ft or more.


Table 9 Lighting design example for a double-8 herringbone milking center.

Location Needed* Illumination Level (footcandles)
Floor Area (ft2) Lamp Type Mounting Height (ft) Lamp Size (watts) Floor Area /Fixture (ft2)   # of Fix.
Parlor Pit
50 228 Fluor. 8** 32W
2 lamps
35 6
Remainder Parlor***  20
759 Fluor.
10 32W
4 lamps 
140 6
Holding & Refl.
Treatment Refr.
10 2,368 Hi-Pres.
10 100W
390 6
Milk Room Lighting
20 217 Fluor. 10 32W
4 lamps
140 2
Washing Area****  100 32 Fluor. 8 32W
4 lamps  
140 1
Utility Room
20 310 Fluor. 10 32W
4 lamps
140 3
Warm  Treatment
20 186 Fluor. 10 32W
4 lamps
140 2
Office & General
50 202 Fluor. 8 32W
4 lamps
70 3
* Determine required number of fixtures by dividing the floor area by the floor area per fixture (Tables).
** Suspend the fixtures for the parlor pit from the ceiling to set mounting height at 8 ft above the pit floor.
***Subtract pit floor area from total parlor room area.
****Hang this fixture over sink area in milk room.

Examples of lighting designs


Figure 2 shows the floor layout for this lighting design example. The milking center has a single return lane, a warm treatment pen near the equipment room, and a naturally ventilated, curtain sided holding area. Additional treatment pens and a catch lane are located alongside of the holding area. The milking center is assumed to be in a temperate or cold climate. Therefore, cold starting capability is needed for the holding area.

Table 9 summarizes the lighting requirements for this double-8 herringbone milking center example. The first step is to identify each zone to be illuminated and obtain the illumination level for that zone from Table 1 (example: parlor pit @ 50 footcandles). Next, calculate the total floor area for that zone and select type of fixture based upon practical mounting height. From design tables 3 through 7, determine floor area per fixture and calculate the number of fixtures needed (example: 228 ft2 divided by 40 ft2).



Figure 2. Lighting Design for a Double-8 Herringbone Milking Center


The free stall barn for this example is a 4-row drive-through with 120 stalls. The barn is assumed to be stocked at a rate of 1.1 cows per stall, resulting in 132 cows housed in the facility. The drive-through feed alley is 144 feet long and lined with a feeding fence on both sides. The fixture mounting height above the feeding alley is 16 feet. The lighting system will be designed to provide 20 footcandles in an area of 28 feet by 144 feet. Figure 3 illustrates this example. High-pressure sodium is the recommended type of lamp because of their low temperature starting characteristics and energy efficiency.

Figure 3. Cross section of a 4-row free stall barn with drive through feeding.

The four design options (listed in Table 11) are for 250 and 400 watt lamps with only a diffusing lens (refractor) and with reflector behind the lamp and a diffusing lens. The two factors that can be used to select the most efficient options are: fixture spacing and lamp wattage per cow. The maximum acceptable spacing for this example is 28.8 feet (1.8 x 16 feet mounting height). Thus, the options that have a lamp spacing of 28.8 feet or less and the lowest installed watts per cow will be the most cost-effective.

In this example the total area to be illuminated is 4,032 ft2 (28 x 144). The number of fixtures are determined by dividing this area by the area each fixture will illuminate. The spacing between fixtures is determined by dividing the length of the barn by the number of fixtures. If this spacing is greater than the acceptable spacing as found above, then this fixture type is not acceptable. The two lighting systems that are worth considering in this example are: (1) a fixture with a reflector and refractor fitted with a 250 watt lamp and (2) a fixture with only a refractor and a 400 watt lamp (bold font in table 11).

Table 11 Supplemental lighting design for a 120 free stall barn to provide 20 footcandles over the feed alley.

High Pressure Sodium
  Reflector + Refractor
Refractor Only
Lamp Size
250w 400W 250W 400W
Floor Area
4,032 ft2 4,032 ft2 4,032 ft2 4,032 ft2
Lamps Per Fixture
1 1 1 1
Floor Area Per Fixture
564 ft2 1,025 ft2 440 ft2 800 ft2
Required Number of Fixtures (Floor Area / Floor Area per Fixture)
8 4 10 5
Fixture Length
2.25 ft 2.25 ft 2.25 ft 2.25 ft
Distance Between Fixtures
15.75 ft 33.75 ft 12.15 ft 26.55 ft
Lamp Watts Per Cow
15.2W 12.1W 18.9W 15.2W

Electrical code

Since dairy barns are damp and dusty environments, either type UF or nonmetallic conduit may be used for wiring. All cable or conduit must be attached to interior surfaces of the building and may not be concealed in the walls, ceiling, attic, or hay mow. Cable can be used, but must be installed in a location where it cannot be damaged. All light fixtures must have a gasket, be fabricated of corrosion resistant materials, and be rated for wet locations (watertight). More detailed information concerning code requirements for wiring in agricultural buildings is provided in the Agricultural Wiring Handbook (NFEC, 1993) and Farm Buildings Wiring Handbook (MWPS-28, 1992).


The many different tasks performed in a milking center require a large range of illumination levels. The best lighting system provides the required amount and quality of light at the least cost. Fluorescent or metal halide lamps that have a color rendition index of 80 or more are recommended for use in the parlor, office, and milk room. High-pressure sodium or fluorescent lamps provide an energy efficient lighting alternative for holding areas. In large free-stall barns high-pressure sodium lamps will best meet the design criteria. When selecting a fixture type and lamp size the total installation and operating costs of the system must be considered. Make sure that all new fixtures and wiring conform to the special requirements of the National Electric Code for livestock buildings and have all new work inspected.


ASAE. 1993. Lighting for Dairy Farms and the Poultry Industry, ASAE EP344.2, ASAE Standards, 40th edition, St. Joseph, MI 49085-9659.

Chastain, J.P. 1994. On-Site Investigation of Indoor Lighting Systems for Dairy Facilities. ASAE Paper No. 945507, ASAE, 2950 Niles Rd., St. Joseph, MI 49085-9659.

Chastain, J.P. 1992. Lighting Requirements for the Milking Center. In: Milking Center Design(NRAES-66), Proceedings from the National Milking Center Design Conference, Nov. 17-19, pp. 214-229, Northeast Regional Agricultural Engineering Service, Ithaca, NY 14853-5701.

Frier, J.P. 1987. Principles of Lighting Design as Applied to Agriculture. ASAE Paper No. 87-3538, ASAE, 2950 Niles Rd., St. Joseph, MI 49085-9659.

Mac Donald, R. and G. Henderson. 1991. Applications of Energy Efficient Lighting Systems in Livestock and Poultry Facilities. ASAE Paper No. 913545, ASAE, 2950 Niles Rd., St. Joseph, MI 49085-9659.

MWPS, 1992. Farm Buildings Wiring Handbook. MWPS-28. Midwest Plan Service, Ames, IA 50011.

NFEC, 1993. Agricultural Wiring Handbook, Chapter 13, National Food and Energy Council, 409 Vandiver West, Suite 202, Columbia, Missouri 65202.

NFPA. 1993. National Electric Code. Article 547. National Fire Protection Association. Quincy, MA 02269.

Peters, R.R. 1994. Photoperiod and Management of Dairy Cows: A Practical Review, In: Dairy Systems for the 21st Century, Proceedings of Third International Dairy Housing Conference, pp. 662-666.

Turner, L.W. and J.P. Chastain. 1995. Environmental Control in the Milking Center. In: Designing a Modern Milking Center: Parlors, Milking Systems, Management and Economics (NRAES-73). Proceedings from the Designing a Modern Milking Center National Conference, Rochester, NY, Nov. 29 - Dec. 1, 1995. pp. 141-153, Northeast Regional Agricultural Engineering Service, Ithaca, NY 14853-5701.

University of Minnesota, U.S. Department of Agriculture, and Minnesota Counties Cooperating


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