I have a friend who refers to his other half as his “solar-powered wife.” This sunshine-dependent woman has learned (the hard way of course) that she is a “high-intensity light” human being, a living organism that functions best when exposed to high-quality (a.k.a. Floridian or Virgin-Islandian) direct sunlight for long periods of time. When plucked from the Southern beaches and planted back into her New England home, this life form withers like so many others who suffer from Seasonal Affective Disorder (SAD).

I’m a “high- to medium-intensity light” person myself. If I didn’t have two small mouths to feed here (and one slightly bigger one), I’d flock to Florida and write from there. Instead I work under a mammoth HappyLite and pretend my feet are in the sand.

Humans are like plants. Some of us require long exposures to intense sunlight while others thrive on very little. Ray. R. Rothenberger from the Department of Horticulture at the University of Missouri-Columbia writes about the different kinds of light various houseplants need. The Chinese evergreen (aglaonema), for example, requires low to medium light intensity, while the spider plant (chlorophytum comosum) demands medium to high intensity sunlight.

As a depressive, I’m intrigued by the process of photosynthesis in plants–how they use sunlight to produce sugar and chemical energy. The word, quite literally, means the “putting together” (synthesis) of “light” (photo). All of life depends on this chemical process, which uses water, light, and carbon monoxide to release oxygen.

Photosynthesis is not all that different from the way we process light. According to Dr. Kevin Keough, this is how light therapy works:

“In simple terms, after light hits our eyes, it travels through the brain to a specific area, causing biological changes that impact how we think, feel, and function. In technical terms, after bright light hits our eyes, it travels along the retinohypothalamic tracts to the suprachasmatic nucleus located in the hypothalamus. From there, it moves to the pineal gland. This complex process triggers hormonal and neurochemical changes that alter core body temperature, melatonin secretion, and serotonin and related neurotransmitter levels. These biological changes ultimately result in fairly rapid changes in our body clock and circadian rhythm that affects how we think, feel, and function.”

None of us could live in darkness. Even the “low-intensity light” human beings and plants. For starters, we’d suffocate because no oxygen would be released into the air we breathe.

That’s why, when it came to creation, God started with light.