Let there be light

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I was reading about Vitamin D this morning and found out that shade produced by severe pollution reduces ultraviolet (UV) energy by 60%. Imagine what it would do to us humans, plants, other species and even solar panels that rely on UV. To begin understanding this, the World Health Organization (WHO) has a good explanation on the difference between kinds of UV radiation. Sun’s light contains – visible light (one that we see and is divided into the seven colors of a rainbow), heat, and UV radiation. UV radiation can be divided into UV-A, UV-B and UV-C radiations. The ozone layer, water vapor and carbon dioxide absorb all of UV-C, almost all but not all of UV-B, and hardly any of UV-A. A lot has been discussed on the relation of these radiations and cancer, which you can read on the WHO page.

Levels of ozone at various altitudes and blocking of different bands of UV radiation. Source: Wikipedia

Let’s say that we are living in a severely polluted city. Except on week days when people usually go to work, people usually can access sunlight on weekends, but do people venture out on weekends? I for one preferred staying in to avoid traffic in Mumbai. Owing to severe pollution, we are already short of our vitamin D shot, plus such sedentary lifestyle is worsening the situation. As for the weather in the US, it is a lot of times cold for me, so I usually sit with my sweater on near my window where I get the sunlight I need. I had asked my husband that I need the sunlight to enter the house in the morning, so we rented a house that would provide us that. It wakes us up naturally, without the need of alarm clocks. I detest taking medicines/supplements and my food doesn’t contain a lot of fatty fishes that provide a lot of this vitamin.

“It has been suggested by some vitamin D researchers, for example, that approximately 5–30 minutes of sun exposure between 10 AM and 3 PM at least twice a week to the face, arms, legs, or back without sunscreen usually lead to sufficient vitamin D synthesis and that the moderate use of commercial tanning beds that emit 2%–6% UVB radiation is also effective.” Now where are we between 10 AM and 3PM? – Source: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

On weekdays, during work hours I used to take a few minutes out of my schedule to soak in some sunlight. Not many companies and especially big buildings/corporates have such spaces and high-rise skyscrapers are so-called gas chambers – a case of bad indoor air quality. Nor are we are not getting the sunlight we need sitting in these skyscrapers neither in our cars.

A really good explanation on how plants use light is given here. Plants definitely do not use a lot of the green light in the spectrum because if it did we wouldn’t see their green color. How about plants in greenhouses, do they get the sunlight they want? UV is also known to cause damage to plants but plants have evolved to use it for them instead of against them. UV-B in sunlight actively promotes plant survival. It helps them keep pests and pathogens at bay. Artificial lighting such as those used in vertical farming these days, contains the blue and red region of the light spectrum needed for plants to grow. The primary light harvesting chlorophylls absorb light in the blue and red regions whereas carotenoids absorb in the blue and green regions. However, a simple light bulb won’t help grow a plant simply because it will lack this region of the spectrum. David Latimer’s bottle garden is another testament to plants living inside a glass structure. His bottle garden is a closed system that has been going on for more than 50 years, without any external input after it was closed. All it needed was a bit of sunlight.

Last but not the least, consumption of sunlight by solar panels. As mentioned on my previous blog on basics of solar power, sunlight is made of a range of wavelengths of lights – the electromagnetic spectrum. Silicon absorbs light of wavelengths close to the visible range. Photovoltaic response curve – solar cell output plotted against wavelength will show the wavelengths absorbed. In order to harness the entire spectrum, scientists have to engineer new materials. The effects of atmospheric pollution, according to this paper, may vary depending on the kind of solar cell.

P.S.: “Let there be light” is an English translation of the Hebrew יְהִי אוֹר (yehi ‘or). The phrase comes from the third verse of the Book of Genesis.

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