What are the health dangers of artificial light at night?

Humans evolved to the rhythms of the natural light-dark cycle of day and night. The spread of artificial lighting means most of us no longer experience truly dark nights.

Research suggests that artificial light at night can negatively affect human health, increasing risks for obesity, depression, sleep disorders, diabetes, breast cancer and more.

Like most life on Earth, humans adhere to a circadian rhythm — our biological clock — a sleep-wake pattern governed by the day-night cycle. Artificial light at night can disrupt that cycle.

Our bodies produce the hormone melatonin in response to circadian rhythm. Melatonin helps keep us healthy. It has antioxidant properties, induces sleep, boosts the immune system, lowers cholesterol, and helps the functioning of the thyroid, pancreas, ovaries, testes and adrenal glands. Nighttime exposure to artificial light suppresses melatonin production.

Here are some articles to research that has been done on the effects of lighting on our health:

This 2009 study by Dr. Richard Stevens, of the University of Connecticut, compared cancer rates and the presence of light at night across 164 countries and found that women in industrialized, highly lit countries had a 30 to 50 percent higher risk of breast cancer than those in countries with less light pollution.

This summary from Harvard University states “Study after study has linked working the night shift and exposure to light at night to several types of cancer (breast, prostate), diabetes, heart disease, and obesity. It’s not exactly clear why nighttime light exposure seems to be so bad for us. But we do know that exposure to light suppresses the secretion of melatonin, a hormone that influences circadian rhythms, and there’s some experimental evidence (it’s very preliminary) that lower melatonin levels might explain the association with cancer.”

Light at Night, Shiftwork, and Breast Cancer Risk
Johnni Hansen
J Natl Cancer Inst (2001) 93 (20): 1513-1515.
DOI: https://doi.org/10.1093/jnci/93.20.1513

Night shift work, light at night, and risk of breast cancer.
Davis S, Mirick DK, Stevens RG
Journal of the National Cancer Institute. J Natl Cancer Inst. 2001 Oct 17;93(20):1557-62.

Missing the Dark: Health Effects of Light Pollution
Ron Chepesiuk
Environmental Health Perspectives
2009 Jan; 117(1): A20–A27.

What can I do about obtrusive security flood lighting?

Security lighting is often not installed correctly. It should only be directed where it is needed, any light spilling over this area, onto the road or your property, is wasted energy (and wasted money), and as well as being a nuisance can contribute to road accidents.

The first thing you should do regarding a security light is to talk to the person who owns it. Explain to them why it is a problem to you (eg shining into your property, causing glare on the road) and show them the Institution of Lighting Engineers leaflet on Domestic Security Lighting. That leaflet is intended for domestic lighting but also applies to security lighting around business premises. Usually by explaining the nuisance, and pointing out how much energy and money they are wasting, the owners of the lights will adjust them.

If they refuse there is unfortunately very little you can do as there are no legal provisions that deal specifically with light pollution. However if the light is causing dangerous glare onto a road, or is causing you severe distress you should speak to the local Gardai.

… architectural and garden lighting?

It is now very common to see buildings light from the ground and particularly on foggy nights the amount of light going straight into space is quite high. This practice is also becoming common in gardens where people want to illuminate a tree!

There are no regulations specifically about this but talking to the owners is often the best approach to changing their lighting practices.

Show the owners photographs of the building/tree take on a foggy night so that they can see the amount of light going upwards. They may be able to reduce the angle or brightness of the lights so that so much light does not spill into space.

A second consideration is the time when the light is on. business and public buildings do not need to be floodlit when there is noone around to ‘appreciate’ the effect. So turning on the lights at dusk, but turning them off later in the evening when there are fewer people around will save a lot of money are light pollution.

There are specific cases where such lighting may be illegal. This applies in particular to where bats are roosting nearby. Overlighting has been shown to cause bats to emerge later at night which in turn can cause feeding problems and ultimately the reduction of the bat population. All bats are protected in Ireland and it is an offence under the Wildlife Act (1976 & 2000) to intentionally disturb a bat or its resting place its resting place. If there are bats in the area then you should highlight this to the owner and the National Parks and Wildlife Service. For further advice please see Bat Conservation Ireland.

… a streetlight that is shining into my bedroom?

You have no explicit rights (that we have been able to find anyway) to force a light to be removed or altered, however most councils do seem willing to help with cases where a person has a light shining into their premises, particularly a bedroom where it may be causing sleep disruption. Take a note of the lamppost number (usually written on the base of the pole) and call the lighting engineer of your local council. Explain the situation, and ask that they replace the light fixture with one that does not shine into your premises or alternatively install a shield so that the light cannot shine in a particular direction. Have a look at this page to see the shielding that a council installed for one astronomer.

… lighting in a new development?

You need to examine the lighting at the planning stage. Every development is required to display a notice summarising the development and providing a reference to where you can examine the detailed plans. This usually will be your local council office. Depending on the local planning guidelines there may be guidelines on external lighting which you can reference in any submission regarding the development. If not you may still make a submission asking for particular lighting to be specified in the planning permission. This could include specifying that the lighting must be full, cut off, must not cause light trespass and must be energy efficient – these are reasonable requests that a planning authority may act upon.

… getting my council to stop light pollution?

You need to engage with your local councillors and engineers. Many of them will not have heard of light pollution, and may not realise the problems that it causes and the benefits that can be achieved by reducing it. Have a look through the documents on this site and also from our colleagues in the British Astronomical Association’s Campaign for Dark Skies.

… making sure my lighting is non polluting?

Is you lighting brighter that is required for your need?

Is it shining beyond where you need it? Into a neighbours yard or above the horizon?

Is the lighting on at a time when it is not needed?

If you answered yes to either of those questions you may need to look at your lighting. For example replace it with a lower wattage fitting, change the direction of the light, or put it on a timer, or motion sensor to ensure it is only on when needed.