Lighting Guide for Dairy Cow Farms

Cows have dichromatic vision, with photoreceptors primarily focusing on blue and green wavelengths. The visible spectrum perceived by a cow extends approximately from 400 nm to 680 nm, with peak sensitivity at around 451 nm (blue) and 555 nm (green).

Therefore, optimal artificial lighting should emit strongly within this range. A "full" spectrum that includes the critical blue-green wavelengths allows cows to see more clearly, reducing stress and improving desired behaviors (e.g., easy movement toward the milking station).

Cool white light resembling daylight is preferred over "warm" yellowish light, as it provides this balanced spectrum. For example, cool white LED lamps (broad spectrum) outperform traditional sodium lamps (very warm color ~2000 K), as the latter emit primarily at longer wavelengths and lack sufficient blue spectrum.

The goal is therefore artificial light that covers the entire 400-700 nm spectrum, with emphasis on 450 nm and 550 nm, to fully utilize the cow's visual capability.

The color temperature of light (Correlated Color Temperature, CCT) relates to the "warmth" or "coolness" of the shade. Natural daylight corresponds to approximately 6500 K, while a typical white LED lamp can be adjusted to various temperatures.

For cows, moderate to high CCT is recommended, approximately 4000-5000 K, meaning cool white light. This color temperature range provides a balance of green-blue spectrum that resembles daylight and within which cows see better.

Additionally, lighting at this scale (e.g., 5000 K) offers a high Color Rendering Index (CRI), making it easier for staff to observe the condition of animals (skin color, mucous membranes, etc.) – although CRI is less important for the cows themselves.

Light intensity is measured in lux and is a critical factor for the effect on the endocrine system of cows. Studies indicate that lighting levels above 150 lux at cow eye height, for several hours daily, can stimulate production through hormonal changes (decreased melatonin during light, increased IGF-1, etc.).

Practically, 150-200 lux are considered adequate in the area where cows move and rest. In fact, providing lighting ≥150 lux for 16-18 hours has been associated with a milk production increase of 7-8% (with a time lag of about 2-3 weeks until the effect manifests).

Conversely, during the dark period, intensity should drop to very low levels (ideally below 50 lux, or even <10 lux) so that melatonin production is not suppressed.

The term photoperiod refers to the duration of daily light exposure. The Long-Day Photoperiod – typically 16-18 hours of light and 6-8 hours of darkness – is beneficial for dairy cows.

This lighting scheme artificially extends the animals' "day" during winter or in enclosed barns, resulting in higher secretion of prolactin and IGF-1, which stimulate milk production.

Importantly, an uninterrupted dark period of 6-8 hours must be provided – continuous exposure to light 24 hours a day not only does not improve production but can suppress it.

Management for Different Animal Groups

Managing lighting for different animal groups (lactating vs. dry) requires separate spaces or the ability to fully darken dry cows.

This is particularly challenging in summer in Greece when the natural day can exceed 14-15 hours. In these cases, shading or enclosed space may be needed for dry cows, while for lactating cows simply no supplementary artificial light is provided beyond natural daylight.

Research shows that cows that spent their dry period under short days have increased feed intake during that phase and produce more milk in the next lactation.

A question is whether spectrum or light intensity variation is needed during the day to simulate the natural cycle (dawn-day-dusk).

Generally, gradual transition is recommended at the start and end of the photoperiod – e.g., LED lamps slowly increasing intensity in the morning (dimmer) mimicking dawn, and the reverse in the evening. This prevents sudden changes that could stress the animals.

In terms of spectrum, some modern facilities use warmer (reddish) light at dusk/night. As mentioned, cattle don't perceive red light as an intense stimulus – essentially it doesn't stimulate their photoreceptors – so it can be used for nighttime staff inspections without "breaking" the cows' dark phase.

Positive Effects of Proper Lighting

Proper lighting not only increases production but also benefits animal health. Exposure to extended daylight reduces melatonin levels during light time, which is associated with higher activity and feed intake, while simultaneously increasing prolactin and IGF-1 that promote milk production.

At the same time, reduced cortisol (stress hormone) has been observed when cows are under appropriate lighting, suggesting they are not stressed by the environment.

Proper photoperiod also contributes to better immune function and fertility: cows under optimal lighting show more stable estrus cycles and easier detection (also due to good lighting for farmers).

Additionally, a well-lit barn without dark corners reduces startle responses and stress in cows – as shadows and sudden light/dark contrasts can frighten them due to their limited depth perception.

First-Lactation vs Mature Cows

First-lactation cows (first lactation) may respond somewhat differently to lighting compared to mature cows with multiple lactations.

Some studies have observed that the effect of long-day photoperiod on production increase is more pronounced in mature cows, while in first-lactation cows the difference may be smaller or statistically insignificant.

For example, in one experiment, the 18 hours light / 6 hours dark scheme in winter increased production by ~7% in multiparous cows, but had no noteworthy effect on first-lactation cows. This may be because young cows are still developing and have different hormonal dynamics.

Dry Cows - The Importance of Short-Day Photoperiod

As mentioned, dry cows should receive different lighting than lactating cows. Maintaining a short-day photoperiod before calving results in over-response after calving when these cows are again exposed to long-day photoperiod.

These cows have higher milk production in the first weeks of the new lactation compared to those who did not have this "winter" light pause.

Moreover, dry matter intake during the dry period increases under conditions of extended darkness, helping cows maintain body reserves for the upcoming lactation.