Why leaving a light on for pets at night might do more harm than good, according to animal behaviourists

The hallway lamp glows through the night, a soft square under the door. Somewhere on the other side your dog sighs in his bed, or your cat curls into the sofa. Many owners leave a light on because the idea of their animal in darkness feels unkind – as if switching everything off might make them lonely, frightened or confused.

Animal behaviourists say the intention is kind, but the effect often is not. For many pets, the extra light is closer to having the bedroom curtains open onto a street lamp: sleep is lighter, noises feel sharper, and the body never fully believes it is night.

What looks like reassurance to us can quietly disturb the very things that make animals feel safe – deep rest, reliable rhythms and the chance to switch off from the day.

A habit that comforts you more than your pet

Humans are heavily visual. We navigate the world with our eyes first and we link darkness with danger. It is easy to project that onto an animal that cannot tell us what the night feels like from their point of view.

Dogs and cats, in particular, are better equipped for low light than most people realise. They use scent, hearing and whiskers as much as vision, and their eyes are built to work in dim conditions. Rabbits, rodents and many small pets are naturally crepuscular or nocturnal: dusk and darkness are when they feel most themselves.

“Most pets are not ‘afraid of the dark’ in a human sense,” says veterinary behaviourist Dr Leila Morgan. “They are afraid of unpredictability and feeling exposed. Constant light doesn’t fix either of those things.”

When people tell behaviourists “he cries if I turn the light off”, the pattern often turns out to be more complex. The crying tends to follow separation, noise from the street or household movement – not the absence of a bulb.

Why night-time darkness matters for animals

Like humans, animals run on circadian rhythms – 24‑hour body clocks tuned by light and dark. These rhythms control hormone release, body temperature, digestion and sleep–wake cycles. When the environment never properly signals “night”, those systems never fully reset.

Melatonin, the hormone that helps bodies understand it is time to sleep, is produced in darkness. Even relatively low levels of artificial light can delay or blunt that rise. In lab studies, rodents kept under continuous light show increased stress hormones, changes in immune function and altered behaviour.

Darkness is not the enemy of safety; it is part of the safety signal. It tells the body: nothing more is expected of you now.

Dogs tend to do a series of naps through the day plus longer stretches at night. Cats often keep a twilight rhythm – active at dawn and dusk, with spells of rest overnight. Small mammals and birds use darkness as their cue to hide, lower activity and conserve energy. When that cue is weak, rest becomes shallower and more easily interrupted.

Over time, behaviourists see this play out as irritability, clinginess, slower learning and a reduced tolerance for everyday stress.

What can go wrong when the light stays on

A bright hallway or living‑room lamp may not seem dramatic, but to an animal trying to sleep it changes the texture of the night. Shadows move more, noises appear without warning, and the brain stays slightly more alert than it should.

Behaviourists link chronic light-at-night exposure to several common issues:

• Fragmented sleep: pets pacing, repositioning, waking to every sound.
• Heightened vigilance: dogs barking at corridor creaks, cats startling more easily.
• Mood changes: grumpiness with other pets, reduced play, lower frustration tolerance.
• Physical fallout: in some species, long-term light disruption can affect weight, skin and coat quality, and even seizure thresholds in predisposed animals.

For prey species – rabbits, guinea pigs, some birds – constant light can also mean constant visibility. Without a proper dark, enclosed hideaway, they never truly feel off duty.

Subtle signs your pet’s nights are not restful

Owners often miss the warning signs because the pet is not obviously “awake”. Behaviourists tend to look for:

• A dog that is exhausted but still dozes lightly near the door rather than sleeping deeply in a bed.
• A cat that wakes the household repeatedly between 2am and 5am, restless or vocal.
• Small pets thumping, chewing bars or over‑grooming through the night.
• Birds flapping or calling if someone passes the cage after lights-out.

These patterns can have many causes, but the lighting set‑up is one of the simpler things to adjust – and often the one most overlooked.

Different species, different night-time needs

Not all pets need the same level of darkness, yet almost none benefit from a bright, ceiling-level light left on until morning. Species, age and health all shape what “night” should look like.

Pet type	Natural night-time pattern	Better-than-a-bright-light option
Dogs	Mostly diurnal with long night sleep	Dark room, soft night-light only for navigation if truly needed
Cats	Crepuscular; short bursts of night activity	Dark with safe routes mapped; no strong overhead light
Rabbits & small rodents	Crepuscular / nocturnal, rely on cover	Very dim surroundings plus enclosed, fully dark hide
Parrots & pet birds	Need consistent, full dark period	Cage cover or dark, quiet room; no glowing screens nearby

“Think in terms of silhouettes and safety zones, not visibility,” advises behaviourist and trainer Josh Patel. “Your pet needs to know where the edges are and where to tuck away, not to see every corner in daylight detail.”

Older animals and those with limited vision may appreciate a faint, low‑set glow so they can avoid bumping into furniture or missing the litter tray. But that is very different from leaving the kitchen lights blazing so you feel less guilty as you head upstairs.

When a small light genuinely helps

There are situations where a carefully chosen light source can make nights easier for a pet – as long as it is treated like a tool, not a default.

Behaviourists are most likely to recommend some form of low lighting when:

• A pet is new to the household and still mapping the space.
• Vision is impaired, for example with cataracts or retinal issues.
• Cognitive decline (dementia) is present, where disorientation is a risk.
• There are physical hazards, such as steep stairs or a split-level garden accessed at night.
• Multi‑pet tensions exist, and an animal needs to be able to avoid another individual in the dark.

In these cases, the advice is to use a small, dim, indirect light at floor level – not a ceiling light. Warm, amber or red-toned bulbs affect melatonin less than blue‑white light and are less likely to reset the body clock.

Timers and motion sensors can help too. A hallway night-light that switches on only if the dog gets up for a drink is quite different, biologically, from eight hours of constant brightness.

Making the night feel safer without flipping every switch

If leaving a light on is really about wanting your pet to feel secure, behaviourists suggest working on the pieces that genuinely feed into security: predictability, comfort, control and calm.

Simple changes often go further than illumination:

• Set a clear pre‑bed routine. A final toilet break, short calm interaction and a predictable phrase (“bedtime now”) help the animal link events with rest.
• Choose the sleeping spot carefully. Many pets rest better in a quieter back room than in the main thoroughfare where people may wander past.
• Block visual triggers. Thick curtains or blinds reduce flashes from cars, foxes in the garden and security lights that set animals on edge.
• Offer a proper den. Covered beds, crates used positively, cardboard hides for small pets and cage covers for birds all let animals control how visible they are.
• Manage noise. A low fan or white‑noise machine can mask sudden sounds that would otherwise ping a half-asleep brain into full alert.

“A dark, predictable nook that smells familiar will calm most animals far more than a glaring bulb,” says Dr Morgan. “If you would not sleep well in the set‑up, assume your pet will not either.”

Myths behaviourists would like owners to let go of

Certain ideas about pets and darkness are so widespread that they rarely get questioned. Behaviourists consistently challenge a few of them.

• “He cries when I turn the light off, so he must be scared of the dark.”
  Often the crying is tied to you leaving, not the light changing. Try staying in the room with the lights off for a few minutes; if he settles, separation is the real issue to address.

• “Cats need a light because they knock things over in the dark.”
  Healthy cats manage dark spaces extremely well. Night‑time chaos often reflects boredom, under‑stimulation during the day or access to tempting surfaces, not poor vision.

• “A TV or bright lamp left on keeps them company.”
  For many animals, constant light and unpredictable sound are more stressful than silence. A worn T‑shirt in the bed and a steady background noise source, if needed, offer steadier comfort.

• “Young puppies and kittens can’t cope in the dark.”
  What young animals struggle with is being suddenly alone in an unfamiliar environment. Gradual separation training and proximity – for example a crate by your bed – matter more than a ceiling light.

How to change the habit without upsetting your pet

If you have always left lights on, you do not have to switch everything off in one night. Behaviourists suggest a brief transition:

1. Lower the brightness first. Swap a bright bulb for a dimmer, warm-toned one or a small night-light.
2. Shorten the light window. Use a timer so the light goes off an hour or two after you go to bed, once your pet is deeply asleep.
3. Watch and adjust. If your pet’s sleep becomes more settled – fewer night‑time interruptions, calmer mornings – you can move towards full darkness where safe.

Keep the rest of the routine consistent while you change the lighting. Stability around feeding, walks and attention helps most animals take environmental tweaks in their stride.

FAQ:

• Should I turn every light off at night if I have pets?
  In most homes, yes: a naturally dark night supports healthier sleep for animals as well as humans. The exceptions are genuinely visually impaired, elderly or disorientated pets, who may benefit from a very dim, low‑placed night-light for navigation.
• What kind of light is least disruptive if I do need one?
  Choose a small, warm (amber or red) LED at floor level, ideally on a timer or motion sensor. Avoid bright, blue‑white bulbs and overhead lights, which more strongly affect body clocks.
• My bird panics if someone walks past the cage in the dark – should I leave a light on?
  Rather than a room light, use a proper cage cover or move the cage to a quiet room where traffic is minimal. Birds usually rest best with full darkness and reduced disturbance.
• How dark is “too dark” for pets?
  If the space is safe, familiar and free of hazards, most healthy pets cope well with complete darkness. The priority is that they have a comfortable bed or hide, stable temperatures and no risk of falls or entrapment.