Importance of Light:
Light is essential to maintaining normal, healthy physiology. Exposure to sunrise is key to synchronizing our internal body cycles to the external world (so we sleep when it is dark and are alert during the day).
Modern industrial society began to tamper with this system, though. The loss of natural light - in dark apartments, in the workplace, on shift work, etc. - creates a state of light deprivation, making us vulnerable to depressed mood, sleep problems, fatigue, ability to concentrate, and more. Nature, too, posed a new problem when humans began to migrate north, where winter nights are long and dark.
Light levels as measured in lux vary greatly between indoor and outdoor lighting. You can see from the chart below how easy it is to become light deprived in our modern, indoor society.
|
| Indoors at home |
200-500 lux |
| Indoors at office |
400-700 lux |
|
| 5:55 Sunrise |
750 lux |
| 6:10 a.m. |
2,500 lux |
| 6:20 a.m. |
5,000 lux |
| 6:40 a.m. |
10,000 lux |
| 12:00 Noon |
81,000 lux |
| 5:10 p.m. |
10,000 lux |
| 5:30 p.m. |
5,000 lux |
| 5:40 p.m. |
2,500 lux |
| 5:55 Sunset |
750 lux |
|
Although researchers do not have firm numbers, a lot of people are light deprived. Symptoms of light deprivation include:
- Feeling depressed or moody during the fall and winter
- Fatigue, lack of energy, and difficulty getting up in the morning
- Problems getting things done (lack of motivation)
- Reduced social contact (often reduced sexual interest)
- Cravings for carbohydrates and weight gain
Surveys suggest that as many as 1 in 20 people experience full-blown winter depression in the northern hemisphere, and three times as many experience winter doldrums. Far larger numbers experience nonseasonal depression at some point in their lives, often for years at a time. With the recent findings that light therapy can also work for nonseasonal depression - light itself or in combination with drugs, the size of the responsive population multiplies.
