We take an in-depth look at light — blue light, warm white and cool white, as well as the colour spectra coming from common light sources and their potential health consequences.
Circadian rhythms used to be largely governed by the rising and setting of the sun. The human body evolved to be exposed to strong outdoor light in the daytime, and people usually went to sleep soon after it grew dark. In 1879, when the light bulb was invented by Thomas Edison, it heralded profound changes in how society operated. Artificial lighting extended the length of the evening, in turn reducing the average hours of nightly sleep in industrialised countries.
Different forms of artificial light vary in colour temperature, measured in units of Kelvin (K), that rates a light source on the lighting spectrum ranging between red and blue. “Warm white” yellowish lighting is often between 2700 and 3000K, and bluer “cool white” lighting is likely to be between 4000 and 4500K. Warm white globes tend to be more aesthetically pleasing, and have a cosy feel, whereas cool white is colder and more clinical. While exposure to indoor lighting and other forms of artificial light is hard to avoid, measures can be taken to minimise its health impacts and effects on natural cycles.
=Q=
In workplaces, where many people spend large chunks of time, lighting may not be optimal. If the opportunity exists, indoor access to natural light should be seized upon. In order to maximise exposure to healthy light, going outdoors during the daytime is ideal, and has a list of other health benefits including vitamin D intake from the sun, lifting one’s mood and normalisation of one’s circadian rhythm.
Overexposure to blue-rich sunlight can have its drawbacks. It is often recommended to protect the eyes against UVB radiation coming from sunlight, which can cause retina damage, macular degeneration and the risk of cataracts (clouding of the eye’s lens.) Wearing a hat and UV-protective sunglasses is often suggested. However, daily exposure to modest amounts of unprotected sunlight is generally considered healthy. Katie Williams from King’s College London sees this habit during the late teens as reducing the risk of developing short-sightedness in middle age.
Blue light devices
Screens such as computers, monitors, tablets and phones are major sources of blue light, caused by LED backlighting, and have a colour temperature between 6500 and 9500K. In the modern world, screens play a dominant role and are tricky to avoid; they have extended to formerly offline activities such as reading, attending meetings, recording music and filling out a tax return. In Australia and New Zealand, more than about a third of the average individual’s time is spent looking at them.
Digital eye strain is the name given to a range of symptoms often including dry eyes, tired eyes and blurry vision. However, the American Academy of Ophthalmology (AAO) doubts that digital eye strain is caused by blue light, and instead believes that its most likely cause is decreased blinking frequency. The AAO also challenges the idea that blue light from devices can cause eye damage or disease, given that it is far weaker than the blue light emanating from globes.
The circadian cycle
In the evening, production of the sleep hormone melatonin increases, especially when stimulated by darkness and soft light. It peaks in the middle of the night and decreases with the approach of dawn. Where melatonin levels are lower there may be difficulties in falling asleep.
Inevitably this circadian cycle has been disrupted by the modern way of living. Outdoor light is biased towards the blue, with a colour temperature of around 5000–6500K, and is good to be exposed to in the daytime. The average Australian spends about 90 per cent of their time indoors, and for New Zealanders this figure is probably roughly the same. Where people remain indoors during the daytime, they are missing this circadian stimulus.
The primary circadian disruptor is blue light after dark, mostly from devices, which tends to inhibit melatonin production. Nocturnal blue light is linked to an increased risk of prostate and breast cancers. For these reasons, it is recommended to avoid using phones or tablets late at night, especially in bed, and to instead have a one-hour interval between switching them off and going to sleep. To maximise melatonin, the sleeping environment needs to be as dark as possible. Streetlights and other urban light pollution can be problematic, in which case thick curtains or eyeshades may help.
A 2020 Australian circadian study led by Professor Sean Cain was the result of seven years of groundbreaking research. Among its many challenging findings is that the evening light in nearly half of Australian homes is bright enough to suppress melatonin production by 50 per cent. Homes with energy-efficient lighting had higher levels of circadian-impacting brightness than those with incandescent globes. Cain also discovered that people are more light-sensitive than previously assumed, and for some, melatonin production can be suppressed by a light as weak as a candle flame. As a result of these findings, he now keeps evening light levels as low as possible while still being able to see his way around the house.
Some scientists believe that circadian disruption from blue-rich artificial light in the evening and at night may be driving obesity and diabetes. Professor Cain has also associated depression with poor light sensitivity, a sign that depression may be linked to disruption in circadian rhythms.
Screen solutions
A lot can be achieved by tweaking light sources to make them easier on human biology. F.lux is a free program available for computers and some phones that regulates the colour temperature of light from screens to make it yellow in the evening, and red at night. More recently, F.lux has been adapted by Microsoft and Apple, with settings available in Windows 10 (Night Light), and Apple macOS (Night Shift). Other blue-light-blocking phone apps are available, as are anti-blue-light screen protectors for both computers and phones.
Another complementary strategy involves blue-blocking glasses, the most well-known of which are the tinted BLUblox. Some blue-blockers look orange or red, while others are clear. In order to encourage a healthier circadian cycle, these glasses are most useful to wear in the evening but are sometimes used for screen time throughout the day. They can be combined with regular glasses, either by buying glasses that have both magnification and blue-blocking properties, or by adding blue-light-blocking lenses to prescription glasses.
Screen users can make their lives easier by adjusting the brightness of a screen down to the dimmest comfortable level. Another tip is the 20–20–20 rule: every 20 minutes look away at something that is 20 feet (about six metres) away, for at least 20 seconds.
Night shifts
Particularly vulnerable to circadian disruption are night shift workers, due to the way that they work against natural cycles. This can manifest in health issues. Lower melatonin levels at night represent a greater cancer risk, which has caused the WHO International Agency for Research on Cancer to classify this type of work routine as “probably carcinogenic”. For female night shift workers, this suppressed melatonin pushes up oestrogen levels, and there is a higher incidence of miscarriage and stillbirths.
Night shift recommendations include exposure to bright light immediately after waking up, avoiding bright light on the way home from work and blocking out the sun while asleep. Melatonin supplements are sometimes used by night shift workers as a sleep aid, although it is recommended to try other strategies first. Foods such as walnuts, corn and rice are high in melatonin.
Which lighting is healthier?
Traditional lighting sources were burning wood and candlelight. Heavily weighted to the red and yellow, their colour temperature is around 1800–1900K, and being exposed to them is mellow and relaxing.
When buying a globe, there is a choice between warm white and cool white, and also the type of lighting technology. From a health point of view, incandescent is the healthiest, followed by halogen, LED and lastly compact fluorescent and fluorescent tubes. Opt for the dimmest light suitable for the purpose, and after dark this absence of unnecessary brightness will aid melatonin production. Light output is measured in lumens, with about 200 being the bottom of the scale for indoor purposes and 1100 being the top.
=Q2=
Incandescents typically have a warm white colour temperature of about 2400K and do not flicker. The spectral profile of a lighting source is essentially a graph showing its levels of light output across the spectrum, from blue to red. For incandescent globes, the profile is good, starting out at zero at the blue end and ramping up evenly to a maximum at the red end. The downside of incandescents is that they are energy guzzlers, which resulted in them being banned in Australia and New Zealand.
Halogen globes are also flicker-free. More efficient than incandescents, halogens are still energy-inefficient when compared to more high-tech lighting. They were banned in Australia in 2020 but are still available in New Zealand.
Fluorescent lighting has a poor spectral profile, emitting most of its light via few narrow spikes at different points along the spectrum, known as “spectral peaks.” For the older-style fluorescent tubes, this makes it harder for the brain to process, and can be a problem for conditions such as autism, ADHD and Tourette’s syndrome.
Efficient compact fluorescent lamps (CFLs) have the longest list of shortcomings. Some flicker at a subliminal level, which may have adverse effects on people with photosensitive epilepsy, Ménière’s disease or migraines. A restricted light spectrum from their deficient spectral profile can produce a stress response in the body. Those who have electrosensitivity are often affected by the radiofrequency radiation given off by some CFLs, and by the “dirty electricity” electromagnetic field emissions they emit, which is common to all high-tech lighting.
LEDs are the most energy-efficient form of lighting, which is increasing their uptake. As with CFLs, dirty electricity is a problem. The French health agency ANSES takes a critical stance towards LED light, which it sees as a strong source of blue light that causes cellular oxidative stress to the retina. Effects from blue light are greater for children and teenagers because their eyes don’t fully filter it out. This health body is also concerned about glare, in the form of uncomfortable brightness, from high-intensity LED light. ANSES supports moderating light intensity, and one way this can be achieved for LED strip lights is via a diffuser, a largely transparent barrier than makes the visual impact of light more comfortable.
Two notable sources of LED light are street lights and car headlights. The commonly encountered type of smart street light is the unhealthier cool white, which has been calculated to be five times as effective at suppressing melatonin than the older-style high-pressure orange sodium lamps. The American Medical Association has also put in its two cents, calling for LED streetlights to be warm white, with a maximum colour temperature of 3000K.
Both LED and HID (high-intensity discharge) car headlights are strong sources of glare, and some people find them annoyingly blinding on the road, leading to Change.org petitions for them to be banned or dimmed. This aligns with the view of ANSES, which has called for the intensity of these headlights to be reduced.
Therapeutic benefits from light
In higher latitudes, winter is characterised by long hours of darkness. This can be accompanied by what is known as seasonal affective disorder (SAD), a type of depression brought on by a lack of natural daylight and low serotonin levels. It is estimated to affect about 20 per cent of the US population, some more severely than others.
If affected by SAD, people are urged to spend some time outside in the daytime. Even when the sky is dull and grey, it is always brighter outdoors than indoors. Another popular strategy involves the use of a light therapy box that emits light at an outdoor colour temperature, at about 20 times the intensity of typical indoor lighting. Sitting in front of this unit for about 30 minutes per day often makes a big difference.
More broadly, taking a passive role with artificial light exposure is likely to result in suboptimal health outcomes, especially in relation to one’s circadian cycle. Fortunately, there are several solutions to hand.
