Background

** Citizen Science projects are designed for the general population to particpate. No specialist knowledge is required. Experiments/measurements can also be performed by children. **

Which color(s) has sunlight?

If we take a photo of the sun, it appears white. But children often color the sun yellow in their drawings. Which color is correct? Actually, sunlight and "white" light in general consists of a mixture of many different colors! Each colour represents light with a different wavelength and different energy. Blue light has a shorter wavelength and more energy than red light. If this bundle of different light components hit a prism, the different wavelengths are deflected at different angles and this way get separated. Not only prisms can induce such an effect, but also raindrops can do. The resulting color gradient is called "spectrum", or rainbow in the case of raindrops.

The spectral colors are an important characteristic of a light source. They give information on the color temperature (e.g. warm or cold light), but also on the category a light source belongs to (e.g. fluorescent lamp, sunlight, halogen lamp, etc.).

Different light sources have a distinct effect on our wellbeing, health and productivity. Several factors play a role, including light intensity, light color (color temperature) and UV-content - however it is yet unknown which factor is most important.

With this project we aim at measuring the daily light exposure of individuals worldwide and correlate it with their wellbeing and health. Please be aware that your participation is completely anonymous.



Further background

How to measure light spectra

The spectral colors of a light source can be assessed by different techniques. These are typically based on light intereference. A straight forward approach is the use of a diffraction grating, or alternatively a CD. On the next pages, we will explain how you can build your own spectrometer and measure the spectrum of different light sources yourself.

The effect of light on ocular growth

It has been shown that children speding more times outdoors have a lower risk of developing myopia than children speding a lot of time indoors. One possible explanation is that the exposure to bright light protects against myopia.


The effect of light on psychological wellbeing

It has been shown that light plays an important role for our psychological wellbeing, and in particular also for psychiatric conditions.

Positive effects: Several studies reported positive effects of bright light on attention-deficit / hyperactivity disorder (ADHD), Parkinson's disease, Alzheimer's disease, obesity, healthy eye development in childhood and sleep disorders. Light therapy evidenced anti-depressive effect sizes "equivalent to those in most anti-depressant pharmacotherapy trials" according to a rigorous review by the American Psychiatric Association Council on Research in 2005. The dose-response curve for light therapy has a practical optimum at 30 minutes of exposure at 10'000 lux, or at at 750 lux when using blue-enriched light (wavelengths around 460nm). In general, positive effects on cognitive functioning were observed with more natural electrical lighting at workplaces.

Negative effects: On the other hand, light pollution and blue light at night or previous to bedtime were reported to show detrimental effects in healthy adutls.


References:

1. Sherwin, Justin C., et al. "The association between time spent outdoors and myopia using a novel biomarker of outdoor light exposure." Investigative ophthalmology & visual science 53.8 (2012): 4363-4370.
2.Lan, Weizhong, Marita Feldkaemper, and Frank Schaeffel. "Intermittent episodes of bright light suppress myopia in the chicken more than continuous bright light." PloS one 9.10 (2014): e110906.
3. Ngo, Cheryl, et al. "Does sunlight (bright lights) explain the protective effects of outdoor activity against myopia?." Ophthalmic and Physiological Optics 33.3 (2013): 368-372.
4. Torii, Hidemasa, et al. "Violet light exposure can be a preventive strategy against myopia progression." EBioMedicine 15 (2017): 210-219.
5. Schwartz RS, Olds J. The psychiatry of light. Harvard review of psychiatry. 2015;23(3):188-94.
6. Lam RW, Tam EM. A Clinician's Guide to Using Light Therapy: Cambridge University Press New York, NY, USA; 2009.
7. Gordijn MC, Meesters Y. The effects of blue-enriched light treatment compared to standard light treatment in seasonal affective disorder. Journal of affective disorders. 2012;136(1):72-80.
8. Golden RN, Gaynes BN, Ekstrom RD, Hamer RM, Jacobsen FM, Suppes T, et al. The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. American Journal of Psychiatry. 2005;162(4):656-62.
9. Arns M, van der Heijden KB, Arnold LE, Kenemans JL. Geographic variation in the prevalence of attention-deficit/hyperactivity disorder: the sunny perspective. Biological psychiatry. 2013;74(8):585-90.
10. Rutten S, Vriend C, van den Heuvel OA, Smit JH, Berendse HW, van der Werf YD. Bright light therapy in Parkinson's disease: an overview of the background and evidence. Parkinson's disease. 2012.
11. Figueiro M, Plitnick B, Lok A, Rea MS, editors. Tailored light treatment improves measures of sleep, depression and agitation in persons with dementia living in long-term care facilities. Poster presented at the annual meeting of the Associated Professional Sleep Societies, Minneapolis, MN; 2014.
12. Danilenko KV, Mustafina SV, Pechenkina EA. Bright light for weight loss: results of a controlled crossover trial. Obesity facts. 2013;6(1):28-38.
13. Wu P-C, Tsai C-L, Wu H-L, Yang Y-H, Kuo H-K. Outdoor activity during class recess reduces myopia onset and progression in school children. Ophthalmology. 2013;120(5):1080-5.


Ophthalmic Personalized Treatment & Imaging Cluster
Computer-assisted Applications in Medicine Group
Computer Vision Laboratory - ETH Zurich
Sternwartstrasse 7
8092 Zurich, Switzerland
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