It may be our friend or foe, but it is a basic necessity of life for every human being: light. Yet we know very little about it, journalist Gemma Venhuizen realised, although for several years she has noticed sometimes sharp differences in her mood. For articles, she sometimes travels to countries where it barely gets dark, discovering the euphoria that the abundance of light can give. At the same time, in the Netherlands, she increasingly suffered from winter blues at the end of the year. 'That aroused my curiosity about what light actually does.'
Some 3 per cent of the Dutch suffer from winter depression, and another 8 per cent from a slightly milder form. They benefit from light therapy: three-quarters of an hour every morning at 8 o'clock for a week in front of a 10,000-lux light bulb. For more severe forms of depression, light therapy is usually combined with medication and sleep deprivation: by not sleeping at all for a few nights, the sleep-wake rhythm is reset. Incidentally, winter depression can also occur in summer: lack of light can also come from too much sunlight. Summer depression also exists, as a result of too much light.
Furthermore, light therapy can help with complaints due to premenstrual syndrome, psoriasis and acne. Skin allergy PLE can be treated by exposure to UVB, which causes the skin to create a kind of protective layer against sunlight. Even in treating some types of skin cancer, light is used: a light-sensitive substance is applied to the site of the tumour cells, a kind of bomb, which is "detonated" by light. UV radiation and vitamin D inhibit colon cancer, and reduce the risk of diabetes, stroke, high blood pressure and cardiovascular disease. Research is being done on the impact of light on borderline, manic depression and eating disorders.
Morning light
Why is morning light in particular so important?
'Morning light works like a switch. It is blue, and that inhibits the production of the "sleep hormone" melatonin. So it makes you alert. Our biorhythms are not exactly in sync with our 24-hour diurnal rhythm; young people tend to have a fairly long cycle of about 25 hours, older people often have a cycle of about 23 hours. As a result, your rhythm becomes increasingly out of sync anyway. This is even more true for evening people. In our society, however, you are more or less expected to be a morning person. So for evening people it's a bit of a choice between going to bed late and getting up early, and thus building up a sleep deficit, or staying up late and getting too little light. As a result, evening people are more likely to suffer from depression.'
On the one hand, we often catch too little (blue) light, while on the other hand we catch too much due to all the electronics.
'That's right. That's the problem with screens: they contain relatively high levels of blue light. That is disastrous for our sleep. With a computer and smartphone, you sit much closer to the screen than with a television. Moreover, many people even use those devices in bed. The suction effect is also greater; the tendency to look at the screen continuously is greater on a tablet or phone than on a television. But these days there are also more and more LED TVs or other forms of LED lighting. I can imagine that will have consequences.'
We are becoming not only bad sleepers but also bad viewers because of the use of these devices. Will we all be wearing glasses in 20 years?
'An eye researcher at the Erasmus Medical Centre has predicted that by 2020, between 10 and 20 per cent of young people will be nearsighted. In Singapore, even nine in 10 young adults are currently nearsighted. In Asia, you can indeed see a frightening increase, although a genetic component also plays a role there. A Chinese study measured the visual acuity of 1 900 pupils. The students were 6 when the study began, and at that time 5 per cent had glasses. By the end of high school, 90 per cent needed lenses or glasses because of myopia. The study found that the number of children who need to wear glasses decreases by a quarter if they play outside for 40 minutes longer per day.'
When the skin catches sunlight, it immediately leads to burns against which no sunscreen provides adequate protection. People suffering from this can usually only go outside if they are thickly dressed. Polyformal light eruption, PLE, is the most common form of light allergy: almost one in five people have it. In mild cases, a person gets bumps; in more severe cases, even the slightest bit of sunlight causes a red rash and unbearable itching. Its more severe variant is called CPLD, chronic polymorphic light dermatosis.
Artificial light
Although the effects of artificial light and daylight are similar, they are not interchangeable. Why not?
'Even when it is grey and cloudy outside, natural light is irreplaceable. On a clear day, the light outside is 100,000 lux, with veil clouds it is still 10,000 lux. The amount of light in an office is 500, an average house 200, so the amount you get outside is many times greater than lamp light. This book has made me much more aware that it is really important to go outside enough. Daylight also increases productivity and gives a greater sense of security than artificial light. This is also why it is very important for offices to have enough windows. You might be able to get vitamin D from a jar, but the benefits of daylight can't really be outweighed by medication and lamps.
- Go for a walk every morning before work, and also in your lunch break;
- Ensure regularity in your sleep-wake rhythm;
- Don't walk with sunglasses on all the time, sometimes the light needs to be able to reach you too;
- Preferably place your desk near a large window, as daylight increases concentration and productivity;
- If you suffer from winter depression, go on holiday to a sunny destination at the beginning of autumn, it will benefit you all winter;
- Get a dog.
At the same time, there are still many gains to be made with lamps. Various experiments have shown that the quality of light in nursing homes and old people's homes has a great impact on how elderly people and dementia sufferers function. The same applies to classrooms: in good light, children learn better. While creativity and dim light would be a good combination for the handicraft classroom.'
Light even affects your eating habits. How exactly is that?
'In bright light, you appear to make healthier food choices than in dim light. Research showed that in well-lit areas, people were more likely to choose white meat, fish and vegetables and less likely to choose red meat. In dim light, participants were more likely to choose fried foods and sweet desserts, and consumed almost 40 per cent more calories on average. On the other hand, in dimmed light you eat less, and more slowly. So it would be best to have brighter light when choosing and preparing, and eat by candlelight once it is on the table. Then the romance is also spared a little.'
Skin cancer
Your book shows how many contradictory sides there are to light: for example, sunlight causes skin cancer, but light is also used to treat certain forms of skin cancer. What surprised you most during your research?
'The interviews with people who are allergic to light were the biggest eye-opener for me. It made me realise how natural light is in most of our lives and how lucky I am to have it. I sometimes find myself complaining about pimples or wrinkles, but actually I should be grateful to my skin that I can just be outside and enjoy the sun. That can suddenly change from one day to the next, as in the case of a woman I interviewed, Anneke: she suddenly became severely allergic to sunlight, as well as to LED and halogen light, when she was thirty-five while on holiday. That can happen to anyone just like that all of a sudden.'
Light. Impact on body and mind by Gemma Venhuizen was published by AtlasContact.
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