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ASAE Conference Proceeding

This is not a peer-reviewed article.


C.A. Gooch, P.E., D.C. Ludington, Ph.D.

Pp. 95-104 in Fifth International Dairy Housing Proceedings of the 29-31 January 2003 Conference, (Fort Worth, Texas, USA), ed. K. A. Janni. ,Pub. date 29 January 2003 . ASAE Pub #701P0203


Photoperiod manipulation, also known as long-day lighting, has been well documented to increase milk production in lactating dairy cows during relatively short time frames in controlled research settings. Dairy producers regularly request information relative to the design of a photoperiod lighting systems for their barns. Many variables exist and need to be investigated in order to perform a prudent design. This paper discusses each design variable and how it relates to the design and maintenance of the resulting lighting system. Proposed installation options are presented for several barn configurations based on their contemporary building dimensions. Suggested lighting system maintenance schedules are provided based on initial design assumptions and their impacts are discussed.

KEYWORDS. Photoperiod, lighting, dairy housing, dairy profitability


Photoperiod manipulation, also known as long-day lighting, is the management practice of using a designed lighting system to increase the light intensity and extend the duration of light which a lactating cow typically is exposed to in a naturally illuminated barn with the goal of increasing milk production. Photoperiod manipulation was first pioneered in the late 1970’s and gained widespread industry interest in the late 1990’s. Supplementing lactating cows with 16 to 18 hours of continuous light at an intensity of 161 to 215 lux (15 to 20 footcandles [fc]) has been shown to increase milk production from 5 to 16 percent above cows exposed to less than 13.5 hours of light in research trials (Peters et al., 1978, 1981; Marcek and Swanson, 1984; Stanisiewski et al., 1985; Bilodeau et al., 1989; and Phillips and Schofield, 1989). Research has also shown that the balance of the 24-hour period needs to be dark in order to achieve a favorable response.

Research reports from photoperiod manipulation studies mainly focus on cow-related effects and provide little information relative to the lighting system designs employed. Light levels are generally reported, but those reports lack other key lighting design information. Consequently, limited dairy-specific background information is available for lighting designers to use when designing lighting systems for photoperiod manipulation. The objective of this paper is to provide information for designing lighting systems for photoperiod manipulation based on experience obtained from designing systems for several commercial dairy barns including six production dairy farms (three tie stall barns and three freestall barns) that participated in a field trial in New York State.

Lighting Design Considerations

Producers intending to employ photoperiod manipulation should consider two groups of variables when designing their lighting systems: barn specific variables and luminaire specific variables. Barn specific variables include size and spatial issues. Luminaire specific variables include those variables that influence the design and maintenance of the light source. Both barn specific and luminaire specific variables are identified and discussed below.

Barn Size

Barn length, ceiling height and width affect lighting design by influencing the total number of luminaires required to achieve a target light level. Wider barns generally require more rows of luminaires to provide target illumination levels. Experience has shown that most two-, three-, four- and six-row barns need at least one, two, three, and four rows of lights, respectively, to provide adequate lighting for photoperiod management. The exact number of rows required also depends on the type and design of the chosen luminaire and its mounting height and is best determined on a case-by-case basis.

Type of Lamp and Ballast

Dahl (2001) reported that metal halide (MH), high-pressure sodium (HPS), and fluorescent (FL) luminaires can be utilized in photoperiod controlled barns as they all create a positive milk yield response. Dairy producers may have personal preferences with regard to FL, MH and HPS luminaires due to lighting efficiency (lumens/Watt), color rendition index (CRI), and useful life. From an efficiency standpoint, in general, FL and HPS lights deliver more lumens per Watt than MH (based on reviewing manufacturer’s literature). This is obviously an economic advantage because fewer luminaires are needed to obtain the target light level (number of lumens measured at the work plane) and also results in a lower connected electrical load (kW).

Fluorescent and MH luminaires have a higher CRI than HPS. (CRI is a measure of the luminaire’s output light color [IESNA, 2000]. A CRI value of 100 represents the highest degree of true color.) Some producers have initially installed HPS luminaires due to the economic advantages but ended up removing them and installing MH luminaires due to the more appealing light color. MH luminaires have an output light color that is closer to white (higher CRI value) while HPS luminaires have a yellowish/orange output color (lower CRI value). From a lamp’s useful life standpoint, FL lamps have the greatest life, then HPS, followed by MH. Lighting system designers should consult with the dairy producer to determine their preference for luminaire options.

Fluorescent lamps have a low lamp lumen depreciation (LLD) factor, or in other words, they stay brighter longer than other lamp types. In fact, mean light output (defined as the light output after 40 percent of average lamp life) for fluorescent lamps can be 90 percent of the initial light output, while MH may be 65 percent based on one manufacturer’s literature. A comparison of the LLD for four lamps is shown in Figure 1. The rated average life for fluorescent and MH lights is determined when 50 percent of the installed lights are still operating.

There are two methods of starting metal halide lamps: standard (MH) and pulse start (MHPS). The approximate lumen output per input Watt for the three high intensity discharge (HID) fixtures are HPS – 97, MHPS – 90, and MH – 80 based on manufacturer’s literature. There is an economic advantage to using luminaires with higher efficiency because fewer luminaires are needed to obtain the same average light level (number of lumens measured at the work plane) and lower connected load (kW). However, uniformity of light level will be less. Achieving “uniform” lighting is easier to provide when using more, lower wattage fixtures.

Pulse start MH luminaires have higher initial light output and a lower LLD factor when compared to standard probe start MH luminaires.

Figure 1. Relative light output for T-8 fluorescent, high pressure sodium, standard metal halide, and pulse start metal halide lamps as a function of hours of operation. (Source: Fetter and Barnett, 2000)


Design of Light Diffuser

The distribution of light (lumens) from a fixture varies with the design of the luminaire’s diffuser (lens). This can have a significant effect on the number and location of the luminaires. A manufacturer’s photometric data should be consulted and used when evaluating a specific luminaire with respect to the intended mounting height. A comparison of four combinations of housings and lenses for a 250 W MH luminaire is shown in Figure 2. The net effects of the different combinations show that the light intensity can vary from 130 to 237 lux (12 to 22 fc) immediately under the luminaire and from 150 to 215 (14 to 20 fc) at a midpoint location, demonstrating the importance of utilizing manufacturer’s photometric data when performing lighting designs.

Figure 2. Comparison of different combinations of housings and lenses for a 250 W low bay pulse start luminaire. Luminaire spacing and mounting height of 7.62 and 5.12 m (25 and 17 ft), respectively. (Adapted from manufacturer’s photometric data.)


Luminaire Mounting Height

The mounting height is generally defined as the distance from the work plane (discussed below) to the bottom of the luminaire when a luminaire with a light diffuser is used. Mounting heights will vary significantly depending on the structural design of a barn. Barns that use a conventional truss system usually will have luminaires mounted to or suspended from the bottom chords of the trusses, or they may be mounted between and flush with the bottom of the trusses to increase the mounting height. With a given sidewall height, this results in mounting heights that are generally lower than those obtained in barns that use a rafter system or a glue-laminated arched truss system. The mounting height with respect to the building’s structural system must be kept in mind when evaluating luminaire options. Examples of outfitting various barn layouts using different structural systems with luminaires are shown in the Appendix.

Work Plane Height

Work plane height is the distance above the floor surface that a lighting intensity measurement is taken. For photoperiod manipulation, the work plane height is the distance between the floor surface and the eye of the cow. The height of the work plane (cow’s eye) will vary depending upon whether the cow is eating at the feed bunk/manger or resting in the stalls. Targeted light levels of 161 to 215 lux (15 to 20 fc) are desired at cow eye level to create a response (Dahl, 2001). Using a work plane height of 60 cm (2 ft) will ensure that the target light level is achieved or exceeded at possible cow eye level locations.

Reflectivity of Interior Surfaces

Reflectivity levels for walls, ceiling, and the floor impact the number of luminaires needed to provide desired light levels. Higher surface reflection coefficients result in increased light levels measured at the work plane. A lighting designer should not use the reflectivity levels found in barns that are new, since dirt quickly builds up on walls, ceiling and floor surfaces resulting in measurable losses in reflectivity. Reflective values for walls range from zero for freestall barns (worst case scenario is curtains fully open) to 10 percent for conventional tie stall barns (minimum light reflected off walls due to normally dirty conditions). Values for ceilings are generally zero since most ceilings (if present) are dirty and/or the selected luminaire is designed to direct light predominately downward. Floors generally have little light reflectance since they are covered with manure; ten percent is suggested and can be considered a conservative design value.

Light Loss Factor

Light loss factor (LLF) is a function of lamp lumen depreciation (LLD), luminaire dirt depreciation (LDD), and room surface dirt depreciation (RSDD); LLF = LLD x LDD x RSDD. Lamp lumen depreciation is a measure of the decrease in lumen output of a luminaire due to use. Manufacturers of lighting equipment have LLD data tables for their products, and LLD is influenced by the operating cycles (on/off frequency). For MH luminaires, an operating cycle of 11 hours on and 1 hour off is suggested by the Illuminating Engineering Society of North America (IESNA), while a 3-hour cycle is suggested for fluorescent lamps.

The effect of LLD on light output for five different luminaries is shown in Figure 3 (400 W standard MH, 320 W pulse start MH, 350 W pulse start MH, 360 W pulse start Stay Bright, and a 360 W Watt-Miser). All the pulse start luminaries have lower LLD than the standard start MH. Operating the lighting system for 16 hours per day for photo manipulation equates to an annual operating time of 5,800 hours. Using this time period, the standard MH the lumen output is reduced by nearly one-third while the lumen output from the 350 W MHPS lamp is decreased by only 21 percent.

Figure 3. Lamp lumen depreciation for metal halide lights with various wattages and lamp strike methods. (Adapted from manufacturer’s photometric data.)


Luminaire dirt depreciation is a measure of the decrease in lumen output of a luminaire due to dirt build up on the luminaire’s diffuser. The accumulation of dirt is a function of the environment the luminaire is exposed to. Significant dirt build up occurs from dirt particles settling on the light diffuser as well as particles attracted by electrostatic forces. Fly dirt also is commonly deposited on diffusers in dairy barns. While significant design data exists for dirt depreciation of luminaires used in residential, commercial, and industrial settings, no similar data exists for dairy facilities. Therefore, at this time designers must use data from tables developed for those applications to approximate the environment found in dairy barns. The authors plan to develop more applicable dirt depreciation design data from the field study data.

Since both LLD and DDF are a function of time, designers must design lighting systems that provide the target light level at some point of time after lights are first turned on. For photoperiod controlled lighting systems, design calculations have shown that initial target light levels of 215 to 270 lux (20 to 25 fc) are needed in order to provide a minimum of 160 lux (15 fc) after 2 years of service life, based on using DDF values that represent a moderately dusty industrial environment. Lighting systems for freestall barns largely consist of using MH or HPS high intensity discharge (HID) luminaires. Considering the LLD factor for these luminaires, the suggested relamping schedule is 2 years. Using data from industrial applications to approximate the DDF in a dairy environment, it is recommended at this point that the luminaires be cleaned every six months.

A well-designed photoperiod lighting system will specify luminaire relamping and cleaning schedules. Systems designed with more frequent maintenance schedules will require fewer fixtures and therefore less initial capital to install them and less cost for operation. However, the increased maintenance frequency will result in increased annual maintenance costs.

Impact of Air Temperature

The temperature of the air adjacent to a luminaire can affect its lumen output. HID light fixtures are not significantly affected by low ambient temperatures because the emitting surface has greater protection from the ambient air. However, the light emitting surface for fluorescent lamps is a tube that has less protection and is adversely affected by ambient temperature, as shown in Figure 4. Light output from this fluorescent lamp is 100 percent at 4C (40F) but is reduced to approximately 50 percent when the temperature drops to –6C (22F). This would be a major problem in most freestall barns, but tie stall barns can use fluorescent lighting because temperatures are moderated in extreme winter conditions. However, older freestall barns that have low, less than 3 m (< 10 foot) sidewalls may require fluorescent fixtures to illuminate the outside rows of stalls. If this is necessary, high output fluorescent fixtures should be considered and adjustments for reduced lumen output should be made.

Figure 4. Effect of ambient air temperature on light output for a T-12 high output luminaire. (Source: IESNA, 2000)


Electrical Demands


The electrical demand needs to be calculated for each different luminaire that is used. The total demand for each luminaire consists of the demand created by the lamp (bulb) and the ballast. Many times the ballast demand is incorrectly omitted from calculations because manufacturers market luminaires based on the wattage of the lamp only. The input power for HID luminaires is approximately 115 percent of the lamp wattage. Using an average value of 115 percent, the total demand for the manufacturer’s 250 W fixture is 285 W. The number of luminaires on a single lighting circuit must comply with the National Electric Code (2002).

Control Clocks

High intensity discharge luminaries used for photoperiod manipulation all have ballasts, which means there will be an inrush electrical current when the luminaire is energized. The current rating for ballast loads (electrical timers, for instance) is considerably lower than for resistive loads. One commercially available timer/controller has a rating of 30 amps resistive load and 6 amps ballast load. Solid state relays will handle inrush current 10 times the rated current. Appropriately sized magnetic contactors are also suitable.

In-Barn Shadows

Freestall barns that use conventional truss systems that are not clear span and/or use convective cooling fans to provide summertime heat stress relief may require special attention when designing lighting systems due to shadowing. It is not understood at this time if in-the-barn shadowing adversely affects photoperiod response.

Uniformity of Light Level Along Feed Alley and Front of Stall

Uniform light levels over the entire floor area of a freestall barn does not appear to be necessary. However, light levels in the cow head area of freestalls and feed bunks (where the comfortable cows will spend most of their time) should be designed to provide a minimum level of 161 lux (15 fc) after a specified service period based on a predicted light loss factor. The Appendix has examples of both targeted lighting design (lighting areas where cows are doing productive activities, i.e., eating or resting in stalls) and uniform lighting of all cow areas.

Light Level for Dark Period

The definition of “dark” during the 6 to 8 hour lights off period does not appear to be well quantified in research reports. Dahl (2001) indicated that all photoperiod lights should be turned off during the continuous dark period. The use of security lights or other night lights is generally not recommended as light levels above 52 lux (5 fc) is believed to adversely affect milk production response. Difficulty arises in providing completely dark periods in large barns on farms that milk three times a day and operate around the clock, and on farms where much emphasis is placed on stall cleanliness and observing cows for general well-being and signs of estrous. Recommendations have been to use low wattage red lights located in barns as a means to provide lighting for human needs during the dark period. Field experience has shown that strings of low wattage (15 W) red lights mounted (spaced 7.3 m [24 ft] apart with a mounting height of 5.5 to 6.1 m [18 to 20 ft] above the floor surface) directly above freestall rows do not provide sufficient light levels in large (4- and 6-row) freestall barns to meet human needs. Minimal lighting was obtained on one of the participating study farms by replacing the red lights with white incandescent bulbs and installing a dimmer on this lighting circuit. By adjusting the dimmer switch, the measured light level at the work plane was lowered to 2.2 lux (0.2 fc) and deemed acceptable by the farm owner when considering his other goals. At 2.2 lux, cows can easily be seen and identified by ear tags, and stall beds can be cleaned and maintained. It is unknown whether providing this low-level lighting during the dark period adversely affects photoperiod milk response.

Lighting for Milking Center

Lighting designs for milking centers generally focus on providing target light levels at cows’ udders. With the implementation of photoperiod manipulation on the farm, the lighting design for the holding area and cow decks must provide the required “lights on”/ “lights off” specifications, and the periods must be synchronized with the overall photoperiod schedule. The “lights on” period is easy to accommodate by designing a lighting system that will provide lighting throughout these areas. The “lights off” period is more difficult due to the continued need to provide lighting for milking purposes. Although not investigated by the authors to date, a suitable system that meets the needs for no light at the cow’s eye yet provides sufficient light at the udder should be able to be designed.


The design of lighting systems for photoperiod manipulation needs to consider two specific groups of lighting design variables: barn specific variables and luminaire specific variables. Barn specific variables include size and spatial issues. Luminaire specific variables include those variables specific to luminaire design and in-service maintenance. Additional research is needed to determine the minimal level of allowable light during the dark period and the uniformity of light needed during the lit period to achieve a response. Minimal lighting is required in many barns due to the presence of near continuous activity that involves humans. This additional information will be helpful to lighting designers.


Bilodeau, P.P., D. Petiticlerc, N. St. Pierre, G. Pelletier, and G. J. Laurent. 1989. Effects of photoperiod and pair-feeding on lactation of cows fed corn or barley grain in total mixed rations. J. Dairy Sci. 72:2999.

Dahl, G. E. 2001. Personal Communication. Associate Professor of Animal Sciences. University of Illinois at Urbana-Champaign.

Fetter, D. and J. Barnett. 2000. Fluorescent Solutions for Industrial Lighting. Energy Users News . May, 2000.

IESNA. Illuminating Engineering Society of North America. Lighting Handbook. 9 th Edition. 2000.

Marcek, J. M. and L. V. Swanson. 1984. Effect of photoperiod on milk production and prolactin of Holstein dairy cows. J. Dairy Sci. 67:2380.

NEC. 2002. National Electrical Code. National Fire Protection Association, Inc. Quincy, Massachusetts 02269.

Peters, R. R., L. T. Chapin, R. S. Emery, and H.A. Tucker. 1981. Milk yield, feed intake, prolactin, growth hormone, and glucocorticoid response of cows to supplemental light. J. Dairy Sci. 64:1671.

Peters, R. R., L. T. Chapin, K. B. Leining, and H. A. Tucker. 1978. Supplemental lighting stimulates growth and lactation in cattle. Science 199:911.

Phillips, C. J. C., and S. A. Scholfield. 1989. The effects of supplemental light on the production and behavior of dairy cows. Amim. Prod. 48:293.

Stanisiewski, E. P., R. W. Mellenberger, C. R. Anderson, and H. A. Tucker. 1985. Effect of photoperiod on milk yield and milk fat in commercial dairy herds. J. Dairy Science 68:1134.


Uniform lighting system for a 3-row freestall barn with conventional truss construction.


Targeted lighting system for a 4-row head to head freestall barn with conventional truss construction.


Targeted lighting system for a 4-row head to head freestall barn with rafter construction.

Targeted lighting system for a 6-row freestall barn with conventional truss construction.

Targeted lighting system for a 6-row freestall barn with rafter construction.


Targeted lighting system for a 2-row tie stall barn with conventional truss construction.