I’m a software dev, product manager and co-founder of Hotels.ng and HNG Internship. I also dabble in embedded systems and hardware projects.

My theory for the dropping global TFR - LED Lighting

Abstract Art

Globally, there is an alarming trend - human birth rates are dropping rapidly. They are not dropping by a small amount, they are collapsing in some countries. For example, South Korea had 500,000 babies in 2007, last year it had 249,000 babies. Half the babies that could have been born were never born. If this continues, soon there will be no more south koreans.

Korea TFR

But what is causing this? There are many theories, but here are the facts we know so far (and I will show how this is connected to lighting):

  • People in cities have far less children
  • People in richer countries have far less children
  • People in countries with better education have far less children
  • People in countries with electricity have far less children

Many different things are correlated with the above points, for example education. And the theories are often around that. But I want us to examine another factor that is correlated with all of the above - Artificial lighting in general, and LED lighting specifically.

Humans do not give birth equally in all months of the year. In the northern hemisphere, children are conceived in the dark months, and come out in the brigher months.

Months humans are born

This not because we have less sex, it’s because the fertility of human varies through the year(1).

Fertility vs Intercourse

To quote the paper:

“Our study allowed us to confirm that seasonal fertility is the main driver of birth seasonality in industrial and post-industrial societies, which has been disputed for at least 150 years. We explicitly tested whether the seasonality of sexual activity is responsible for human birth seasonality. Our models found, universally, that seasonal sexual activity alone cannot explain birth seasonality.”

Basically, humans have sex through the year, but they give birth to kids in the brighter months.

So humans have some kind of internal regulator that determines the best month to give birth. This makes sense - a child born in the winter will have a harder time surviving than a child born in the summer. This is extreme evolutionary pressure, as the child born in the winter will have a much higher chance of dying, and the child born in the summer will have a higher chance of surviving. So the child born in the summer will have a higher chance of passing on its genes.

How does the human body know how to adjust this fertility? The best thing it could use is the amount of light. Perhaps the length of the daytime, or the intensity of light. Adjusting fertility is highly likely to be tied to something related to light.

And now we come in and introduce electric lights. Humans have not had time to evolve to adjust to electric lights. So the human body is still using the same mechanism to adjust fertility, but now it is getting the wrong signals. The human body is getting the signal that it is always summer, and so it is adjusting fertility to be lower. It’s trying to prevent kids from being born in the winter, but now it’s preventing kids from being born at all.

Gas lighting must have had a strong effect on TFR already. Look at the historical TFR of france:

TFR of France

Gas lights where introduced in 1790, and you see the TFR rapidly drop after that.

Since 2015, we have seen an even more rapid drop in TFR. It’s around this time that LED and energy efficient lights have become more common, and one characteristic they have is the blue light spike:

LED wavelength

How about the baby boomer period? Well, that was a small period in the world when the world switched from gas lamps to incandescent lamps. Incandescent lamps do not have much blue light, so they are not recognized as sunlight. They would rather be recognized as “fire”, which we would have evolved to deal with.

Light Spectrum

The introduction of LED lights have now created an eternal summer for human fertility regulator. And it does not want children born in the winter, and so dials down the fertility.

Since 2015, fertility has been plummeting - even faster than before. This corresponds to our extreme use of led lighting - both in energy efficient bulbs and in screens. Mobile phones, computers. We are constantly bathing ourselves in blue light.

If this theory is true, then this will affect all humans, and can lead to our extinction. No government incentives can override biological programming.

Like the germs killed the aliens in War of the Worlds, maybe something so innocuous as bright screens will end up wiping out humanity.

(1) https://www.medrxiv.org/content/10.1101/2020.11.19.20235010v1.full

Last Modified: Jan 12, 2024