Through which parts of the body does the light we receive have an effect? #26

In previous articles, I have shared information about the effects of light.
We are increasingly hearing about the topic that "receiving light has a positive effect on the body."
So, through which parts of the body does that light have an effect?
The most commonly known part is the "skin." And in recent years, it has become clear that the "eyes" also play an important role.

1. Introduction

When you receive light, your internal clock is reset, your sleep improves, and your mood stabilizes.
Such benefits have become widely known.
So, through which parts of the body does light act upon us?

2. Skin: Vitamin D production

• Ultraviolet rays (especially UV-B) synthesize vitamin D in the skin

• Vitamin D is essential for bone health and maintaining immune function.

• The skin has long been noted as an "entry point for light."
  For example, by receiving sunlight, vitamin D is produced, which helps with calcium absorption.

3. Eyes: Adjustment of the internal clock and mental state

• Special receptors in the retina (ipRGCs) react to blue light

• Light sends signals to the suprachiasmatic nucleus in the brain, regulating the internal clock.

• It regulates the secretion of melatonin (the sleep hormone), improving the quality of sleep at night.

• Morning light promotes the production of serotonin (the happiness hormone), which can be expected to have effects such as brightening your mood and reducing stress.

4. How much light should you receive?

• According to the Ministry of Health, Labour and Welfare guidelines (2023), it is recommended to receive1,000 lux or more of light after waking up or during the day.

  1. For reference:

     • Typical indoor lighting → about 500–800 lux

     • Outdoors on a cloudy day → 1,000–5,000 lux (recommended brightness)

     • Sunny outdoors → 10,000 lux or more (even more effective!)
       Point: Since indoor light levels are often insufficient, it is recommended to go outdoors in the morning.

• For preventing myopia in children,international guidelines recommend at least 2 hours of outdoor activity every day.
  In addition to bright light, it is believed that the increased opportunities to play in parks and look at distant scenery reduce the risk of myopia.

5. Summary

The effects of light work through two routes: the skin (vitamin D production) and the eyes (circadian rhythm, sleep, and mental health).
In particular, it is known that "light through the eyes" has a significant impact on sleep quality and mental well-being.
Since indoor light is not enough, getting exposed to light outdoors within the first hour of waking up in the morning is recommended.
Even a habit of just a few minutes is said to regulate your internal clock and make you feel refreshed.

🌅 Small practical tips
Of course, it is more effective if you are conscious of "when and how much light you are exposed to."
However, there is no need to overthink it.

• Open the window and soak in the outdoor light when you wake up in the morning

• Step out onto the balcony with a cup of coffee

• Look up at the sky while walking the dog

With such simple actions, you can take in over 1,000 lux of light.
Rest assured that even on cloudy or rainy days, you are still getting enough light.

👉 Did you get some morning light today?

Note: This article introduces general health information and is not intended for diagnosis or treatment. If you have any concerns about your physical condition, please consult a medical institution.

6. References (APA 7th)

Berson, D. M., Dunn, F. A., & Takao, M. (2002). Phototransduction by retinal ganglion cells that set the circadian clock. Science, 295(5557), 1070–1073. https://doi.org/10.1126/science.1067262

Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3), 266–281. https://doi.org/10.1056/NEJMra070553

Ministry of Health, Labour and Welfare. (2023). Guidelines for healthy sleep 2023 [Sleep Guidelines for Health Promotion 2023]. https://www.mhlw.go.jp/content/10904750/001181265.pdf

Rose, K. A., Morgan, I. G., Ip, J., Kifley, A., Huynh, S., Smith, W., & Mitchell, P. (2008). Outdoor activity reduces the prevalence of myopia in children. Ophthalmology, 115(8), 1279–1285. https://doi.org/10.1016/j.ophtha.2007.12.019

World Health Organization. (2019). WHO package of eye care interventions. https://www.who.int/publications/i/item/9789241516570

7. Related Articles

My own articles

• Regulating yourself just by soaking in light: The science of morning natural light and your "internal rhythm"

• Writing about the importance of light precisely because it's a time when I want to avoid it

Articles by other creators (these can supplement parts I haven't written or where I am lacking)

• The scientific reasons for regulating your mind through sunbathing and how to do it efficiently

• Health benefits of morning walking

• Can the gut change with 'sunbathing'? The surprising relationship between tanning and the gut

• [1-minute read] Morning sunbathing: Why does morning light change your mind and body? Recommended sunbathing to regulate the autonomic nervous system #SleepHack

• Sunbathing while trying to conceive: Vitamin D synthesis through 'hand sunbathing'

• Is 'morning sunbathing' meaningful even on cloudy or rainy days?

• [Refreshed] Morning light is the ultimate alarm clock. The amazing effects of sunbathing proven by science