by Charles Miller

In the 1950s, arriving at the Aeropuerto Internacional de la Ciudad de México by night was a spectacularly memorable experience. For hours, over the drone of the propellers, looking out the window all one could see was darkness punctuated by a few streetlights below that were not much brighter than the stars above. Absent today's light pollution the stars shone brightly. My mother held a pilot's license and that earned her an invitation from the captain to come sit in the cockpit; remember this was the 1950s when that kind of thing was possible. She described as scary the experience of the plane descending as it approached the airport, staring desperately into the absolute darkness unable to make out the line between the stars above and the mountain ridges below. Then suddenly she was looking down into a bowl, a Oaxaca black pottery bowl with a cluster of sparkling diamonds in the center. Laid out below was the valley of Mexico with a warm glow from the streetlights of Mexico City bounded on all sides by the vague, dark outlines of mountains.

That warm glow came from the many incandescent street lights used at the time. The incandescent light bulb, perfected and popularized by Thomas Edison in the 1890s was the worldwide standard for many decades though they were and still are terribly inefficient. Some 98% of the energy consumed by incandescent light bulbs is turned into heat that is wasted when the bulbs are used for illumination purposes.

In the 1960s and 70s the warm yellow glow of incandescent lights was largely replaced with mercury-vapor or florescent light bulbs that had a more blueish-green cast to their color. These types of light bulbs output more lumens and used less electricity so the color of nighttime cities changed from warm yellowish tones to colder blueish color.

Things changed again in the 80s and 90s as cities turned orange with low pressure and high pressure sodium-vapor lighting. Once again, the change was usually driven by economic considerations because the new light bulb technology was even more energy efficient and provided more light. A common complaint was and is that the yellow-orange monochromatic light inhibits color vision in human eyes and for that reason their use was largely restricted to outdoor lighting such as street lamps. It also meant that the experience of looking down from an airplane at night was that the color of many cities changed from mostly blueish back to yellowish.

Over the last decade we have experienced yet another generational change in the world of illumination, this time both outdoors and indoors, even including the smart phone in the palm of your hand. In just a few short years the LED (Light-Emitting Diode) has transformed the world of illumination including street lights, indoor lighting, the screens of your televisions, computers, smart phones, tablets and almost everywhere else artificial lighting is used.

Electroluminescence, the naturally occurring conversion of electric energy to light has been known for a century. But it has only recently taken over and completely transformed the whole world of artificial lighting. Why it has taken so long is a story for next week.

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Charles Miller is a freelance computer consultant with decades of IT experience and a Texan with a lifetime love for Mexico. The opinions expressed are his own. He may be contacted at 415-101-8528 or email FAQ8 (at) SMAguru.com.

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