Sun Exposure · Skin, light & energy
Skin as a Solar Panel: What I Mean by That
What light can do inside cells, how melanin responds to it, and where my solar-panel analogy meets an open scientific question.
When I say my skin is a solar panel, here’s what I’m getting at: sunlight reaches my body and can interact with processes involved in cellular energy. Melanin belongs in that picture for me because of the way it interacts with light.
The analogy points toward a connection worth understanding. It is not a demonstrated account of skin melanin collecting sunlight and passing its energy directly to mitochondria in a person. To see where the evidence takes us, it helps to separate light reaching tissue, something absorbing it, and a response inside the cell.
The energy connection that caught my attention
Jack Kruse describes skin as a solar panel in relation to the brain’s energy needs in his conversation with Max Gulhane, around 1:24. His wider account connects melanin, light, leptin signaling, and mitochondria. That helped shape the way I think about the subject.
The important word for me is energy. Mitochondria are structures inside cells that help produce ATP, a molecule cells use to power their work. The National Human Genome Research Institute explains that role. A claim about light changing ATP production is something researchers can test.
What kind of energy connection?
In ordinary metabolism, cells draw on the chemical energy in nutrients. Mitochondria help convert that energy into a form cells can use. Light could influence parts of that machinery without replacing the food-derived fuel. Think about the distinction between changing how an engine runs and identifying what fuels it.
An increase in ATP tells us that a cell responded. To understand why, we still need to identify what absorbed the light and trace the steps that followed. That is the question I carry through the experiments below.
Light can reach beneath the surface
In a 2025 study by Jeffery and colleagues, a small amount of longer-wavelength sunlight was detected after passing through the chests of seven men. The transmitted light had a different spectrum from the light arriving at the skin. Jeffery et al. (2025): sunlight transmission through the body.
This was a measurement of light transmission. The participants were described as Caucasian, and that small group cannot establish the same transmission across skin tones. The paper also included separate laboratory light experiments; those should not be confused with its sunlight measurements.
Outdoors, wavelength, intensity, duration, clothing, and the tissue involved all affect the question being asked. A selected red-light exposure in a laboratory represents only part of the sunlight setting. These findings do not supply a personal sun-exposure dose, and UV protection remains relevant.
What happens when melanin absorbs light?
Eumelanin, the brown-black form of melanin, absorbs light and can rapidly dissipate the absorbed energy as heat. In a 2022 study, Ilina and colleagues used instruments that track extremely fast changes to investigate this response in pigment preparations and a molecular building block. Their work helps explain a mechanism of photoprotection. Ilina et al. (2022): eumelanin and light energy.
Here, the measured response is heat dissipation. Keep that in mind as we turn to experiments measuring enzymes and ATP: they are examining another response, under different conditions.
What researchers have measured in cells
Photobiomodulation is the study and use of selected light exposures to influence biological activity. In an experiment, researchers can specify the wavelength and amount of light, then measure how cells or tissues respond.
In 2012, Houreld and colleagues used 660-nanometer red light on human skin fibroblasts and mitochondria isolated from those cells. They measured enzyme activity in the isolated mitochondria and ATP in irradiated cells. ATP increased in particular normal and diabetic cell conditions; the response depended on cell condition and dose. Houreld et al. (2012): red light, mitochondria, and ATP.
One enzyme involved is cytochrome c oxidase, part of the mitochondrial machinery that supports ATP production. That helps explain why researchers pay attention to it: a change in its activity might help account for a change in the cell’s energy processes.
The mechanism is still being examined. Quirk and Whelan’s 2016 experiment found no significant change in the reaction rate of isolated cytochrome c oxidase under their red and near-infrared conditions. Different preparations and measurements are involved, so these experiments cannot be reduced to a simple yes or no. They show why the exact process matters. Quirk and Whelan (2016): light and cytochrome c oxidase.
What I mean by the solar panel
The crux of my analogy is energy. We can now be more specific about the pieces: some light penetrates tissue, eumelanin absorbs and dissipates energy, and selected light exposures can change cellular measurements. The experiments establish those pieces under their tested conditions; the proposed transfer from skin melanin to mitochondrial energy remains unestablished.
I believe melanin deserves much more attention. For me, the most useful way to give it that attention is to follow the energy carefully, asking what each experiment actually measured. That makes the solar panel an invitation to investigate, with a clear idea of what still needs explaining.
There is also a more familiar route through which daylight affects us: light received through the eyes helps organize the body’s daily timing. Understanding that pathway gives us another way to think about our relationship with the natural day.
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