Let there be light! Tuesday marks the official opening of the 2015 International Year of Light, a celebration of all aspects of the slice of the electromagnetic spectrum that is detected by our eyes. The opening ceremony is being held Jan. 19-20 in, appropriately, the City of Light: Paris.
About a year ago, the United Nations proclaimed this year to be the International Year of Light and Light-based Technologies. Events will be held worldwide in conjunction with IYL-2015. It is also the centenary celebration of Einstein’s general theory of relativity, which describes how light is bent by gravity. Also, it is the 50th anniversary of the discovery of the cosmic ray background, the microwave glow left from the Big Bang.
Light is fundamental to astronomy: We actually use the whole electromagnetic spectrum, from low-energy radio waves to high-energy gamma rays, in our study of the cosmos. Sure, we’ve brought back several hundred pounds of moon rocks, collected a lot of meteorites, and scraped the surface of a planet and a comet. However, the vast majority of our data have come from the light waves received from celestial objects.
IYL-2015 will also celebrate the production of light, from lasers to LEDs. Astronomers have an interest here, too, since we need an absence of light – darkness. Reducing light pollution is an ongoing effort, as we work to get appropriate light levels and well-designed fixtures that shield the light from the sky. Currently, we are wrestling with the newest lighting technology being implemented: light-emitting diodes.
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LEDs are very efficient, but we have a problem with the widely used “cool white” LEDs, which have a strong blue spike in their spectrum. Blue light is more efficiently scattered by Earth’s atmosphere than other colors. The blue part of the sun’s light is scattered so much that we have a blue sky. For lighting, that means cool white LEDs produce a lot of sky glow. Astronomers prefer the so-called filtered LEDs, which have that blue component filtered out.
Light is essential to life, from the photosynthesis that supports plants to vision enjoyed by the animal kingdom. Eyes are so important that they have independently evolved about 50 times. And about the time we started using our first artificial lighting – fire – we were starting to create special forms of reflected light, patterns of colors we would come to call art. The manipulation of light has become part of our culture.
I hope you take some time to be mindful about light this year, not only seeing it and knowing how you see it, but also appreciating how it is made and how we shape it.
Que la lumière soit!
(“Let there be light!”)
Daniel B. Caton is a physics and astronomy professor and director of observatories at Appalachian State University. Email: firstname.lastname@example.org. More on this month’s column: www.upintheair.info.