Does keeping chickens with the lights on help them grow or make them sleepier?
Installing lighting equipment in a chicken coop has multiple benefits for both keepers and birds – from increasing egg production to providing extra heat (depending on the bulb type). But does more light always mean better results? When the sun goes down, should you turn off those lights? Or can you leave them on all night? Today, let's talk about whether chickens actually need "night lighting" and what's best for their health and productivity.
1. What kind of environment do chickens need to sleep soundly?
Chickens, like humans, are diurnal animals – they wake at sunrise and rest at sunset. Physiologically, chickens have photoreceptors in their eyes and skin that detect changes in light and send signals to the pineal gland in their brain. For domestic chickens, light is the key external factor controlling their sleep‑wake cycle.
In a completely dark environment, the pineal gland secretes large amounts of melatonin. Melatonin is a crucial sleep‑promoting hormone that not only helps chickens enjoy high‑quality rest but also plays an important role in physiological recovery and immune regulation. Therefore, if a chicken coop is lit up all night, chickens will mistakenly think it is still daytime, melatonin secretion will be suppressed, and they will be unable to sleep.
Moreover, a scientific study has shown that just one hour of inappropriate light at night can disrupt the survival of nerve cells in the developing brains of young chickens. This research, using chickens as a model, clearly demonstrates that irregular artificial light at night (ALAN) can have long‑term negative effects on brain development.
2. Why should we avoid all‑night lighting? The dangers of continuous light exposure
In the poultry industry, especially in the early stages of broiler production, long or even continuous lighting was once widely used to increase feed intake and promote weight gain. However, in recent years an increasing amount of scientific evidence has questioned the practice of long or near‑continuous photoperiods, because the drawbacks may far outweigh the expected benefits.
2.1 Fear and stress response
Studies show that when chicks are raised under 24‑hour constant light (24L:0D) during their first week after hatching, they exhibit fear‑related behaviours. Compared with a control group (12 hours light / 12 hours dark), the constant‑light group had significantly higher blood levels of corticosterone (a stress hormone), while levels of melatonin and serotonin (a key neurotransmitter for mood regulation) were significantly reduced. This indicates that a lack of darkness keeps chickens in a prolonged state of high tension and even fear, increasing stress reactions.
2.2 Disruption of behavioural rhythms
Continuous light also disrupts sleep quality. Research has found that although broilers under longer photoperiods (e.g., 20L:4D or 18L:6D – 20 hours light/4 hours dark, and 18 hours light/6 hours dark) may spend more time "lying down", their sleep is of poor quality and very light, and they actually show less quiet resting and true sleep behaviour. In groups where light intensity changes abruptly (turning on/off suddenly), broilers display more alertness and locomotor activity, whereas in groups with gradual light transitions, more sitting and genuine sleeping behaviour is observed.
2.3 Production efficiency and health risks
Although 24‑hour light may increase average daily feed intake, research has shown that it does not bring the expected weight gain; instead, it results in a higher feed conversion ratio, meaning more feed is wasted. Furthermore, nearly continuous light can adversely affect growth rate, mortality, and – most importantly – the immune response to poultry diseases.
3. Scientific light management: adjusting for each growth stage
Given the above findings, we should neither blindly believe in the short‑term stimulating effect of continuous light nor completely abandon the use of artificial lighting. Scientific light management focuses on providing appropriate, regular light‑dark cycles according to the birds' age and production purpose. Recommended schedules for different stages are as follows:
3.1 Brooding period: adapting from light to dark
- First three days: Young chicks have poor eyesight and need to quickly find food and water while adapting to a new environment. Typically they are given 23 hours of light and 1 hour of dark for the first three days. That one hour of darkness is not useless; it trains the chicks to gradually get used to darkness, preventing panic and trampling accidents that could occur later due to sudden power failures.
- From day 4 onward: Light hours should be gradually reduced. Reduce light by 30 minutes per day until day 14, when it reaches 15‑18 hours. By three weeks of age, light hours should finally be decreased to 8‑10 hours and kept stable. Light intensity: use 40‑watt bulbs in the first week, then reduce to 25 watts, ensuring that intensity is not lower than 3 watts per square metre.
3.2 Growing period (rear‑ing): controlling light to prevent early maturity
During the growing period (7 to 20 weeks of age), the key word for light management is "control". Light hours should be neither too long nor too short – 8‑10 hours per day is appropriate. Too much light stimulates premature development of the hens' reproductive organs, leading to early maturity. Hens that start laying too early tend to have lower body weight and smaller egg size, a shorter peak production period, and are more prone to egg‑binding and prolapse. Light intensity during the growing period is best kept at 5‑10 lux.
3.3 Laying period: gradually increasing light for high production
When hens enter the laying period (usually after 20 weeks), light hours must be increased gradually. A common programme is to increase light by 30 minutes per week until the total daily light hours stabilise at 14‑16 hours. For laying hens, the principle is: light duration should be increased rather than decreased, and intensity should be gradually increased, not decreased. Increasing light stimulates the hypothalamus to release gonadotropin‑releasing hormone (GnRH), which promotes follicle development and ovulation. For open‑house systems that rely on natural light, artificial supplementation must be used to maintain a constant total photoperiod, avoiding a sharp drop in egg production when autumn days shorten naturally.
4. Practical tips – details make the difference
Beyond a scientific lighting schedule, everyday management details matter just as much.
Choosing bulb colour wisely – White light (e.g., incandescent or fluorescent bulbs) mimics daylight most closely and strongly disrupts chicken sleep. If you must provide light at night (e.g., during heavy snow or extreme cold for heating) without disturbing rest, consider using red bulbs. Observations show that red light is less likely to be mistaken for daytime, so it has a relatively smaller effect on circadian rhythms. Blue light, on the other hand, tends to keep chickens calm and encourage deeper sleep.
Smooth transitions, no sudden changes – Never turn lights on or off abruptly. A sudden bright flash or instant darkness can cause severe stress, leading to panic, crowding, and trampling. Whether turning lights on or off, it is best to use a dimmer or gradually adjust brightness in steps so the birds' vision can adapt.
Using timers – In modern poultry management, using a microcomputer timer or smart lighting system is essential. It ensures that birds receive stable, regular "sunrise" and "sunset" signals every day, helping them know when to wake and when to sleep. It also greatly reduces the daily workload for the keeper and saves electricity costs.
Pay attention to light wavelength and intensity – Besides the photoperiod (light/dark ratio), light wavelength (colour) and intensity also affect chicken behaviour. For example, research indicates that under dim blue light, broilers are the calmest, spending more time sitting and sleeping; under bright white light, they are more prone to nervousness and aggressive behaviour.
5. Common misconceptions (Q&A)
Q: Will leaving a light on at night keep rats and weasels away?
A: Not really. Protecting against nocturnal predators and rodents relies on reinforcing gaps in the coop and physical barriers. Keeping lights on all night not only fails to effectively deter predators (it may even reveal the chickens' location), but also deprives the birds of normal sleep and reduces their immunity. Some farmers briefly turn lights on and then off at night to catch predators off guard, but that is not the same as 24‑hour illumination.
Q: Do newly hatched chicks need complete darkness at night?
A: Quite the opposite. Very young chicks (0‑3 days old) are weak and have poor eyesight; they cannot cope with total darkness like adult chickens. At this stage, they do need near‑24‑hour lighting to help them find feed and water and to maintain body temperature. As they grow, light hours should be gradually reduced and darkness intervals increased.
Q: Do free‑range native chickens need artificial light management?
A: For free‑range layers, yes, especially in autumn and winter when natural daylight may fall below 12 hours. Scientific trials show that when natural light is less than 12 hours, egg production drops significantly. Thus, free‑range keepers should supplement light in the morning and evening so that total daily light reaches about 14‑16 hours – this ensures a good supply of eggs even in winter.
Q: Is red light completely harmless to chickens?
A: It is relatively harmless, but it cannot replace true darkness. Although red light is less likely to be mistaken for daylight and does not easily interrupt sleep, it only provides a low‑level, dim light source that is not bright enough for intensive feeding and activity. In terms of normal circadian regulation, no type of light can replace the importance of pure darkness for deep sleep and melatonin secretion in chickens.
Chickens are highly sensitive to light. Forcing them to sleep with lights on is essentially imposing physiological stress on them. Whether your goal is higher egg production, faster broiler growth, or better animal welfare, a stable, regular light‑dark cycle that includes necessary darkness is key. Dimming the lights at dusk and letting chickens follow their natural instincts is both the kindest approach to the birds and the most scientifically sound way to improve production efficiency.
