Street Lights

Now an estimated 300,000 million street lights brighten the world.

Street lights create unintended consequences. For example, during the French revolution, they were convenient spots to hang aristocrats. A mob’s cry, “À la lanterne!” was fatal.

Today, street lights have different unintended consequences. They are less dramatic, but more far-reaching, than the murder of aristocrats in Paris.

Mixing Day and Night

Many of us get artificial light at night from street lights. This light suppresses the secretion of the sleep hormone, melatonin.

Newton (1643-1727) shone white light through a prism, and found a spectrum.

Further, this light, while white, includes the blue part of the spectrum. This part of the spectrum energizes us.

 Thus, exposure to light at night makes it is hard to sleep, and weakens our natural circadian rhythms.

The paltry amount of sun most of us get during the day adds to the confusion of our inner clock.  We usually feel we are getting enough illumination when all the lights are on inside our homes and office buildings during the day. However, even then we average much less exposure to light than we would if we were outside on a cloudy day.

Getting the wrong amount of light at the wrong time puts us at risk for insomnia, problems with alertness during the day, and so on. So while street lights serve many useful functions, they also confuse the timing and coordination of many functions, from sleep to digestion.

Shirking the Night Shift

Dr. Knop and her colleagues found that cabbage thistles in lit (vs dark) fields had 13% fewer fruits.

Cabbage thistles had fewer visitors if they had light at night.

Too much light at night is a problem for other living things as well, as Eva Knop, and her colleagues from the Institute of Ecology and Evolution at the University of Bern, demonstrated in August 2017. They added the equivalent of street lights to five fields, and kept five fields naturally dark. They then compared the nocturnal pollination in the two groups of fields.

When the moths, and other insects, were in fields with lights at night, these nocturnal pollinators were far more likely to ignore their pollinating responsibilities. Specifically, nocturnal pollinators were about two thirds less likely to visit the flowers in the meadows with artificial light. This decreased the fruit set, and hence the reproduction, of plants.

“The pollination during the day obviously cannot compensate for the losses in the night,” notes Dr. Eva Knop.

These findings are serious because:

  • light emissions are increasing as residential areas increase worldwide
  • daytime pollinators, such as bees, are decreasing worldwide
  • it appears that nocturnal pollinators indirectly aid daytime pollinators, so a loss of nocturnal pollinators would have a ripple effect.

The Bottom Line

While artificial light can be a blessing, we are just beginning to see, and understand, a new kind of unintended consequences. Unfortunately, these consequences may snowball as we become increasingly urban, while still living in an interdependent web of existence with insects, and plants.

Related Reading

The Danger of Mixing Day and Night

When the Light You See Is Not the Light You Want