Photo by Dimaano Photography

On Monday night, I caught myself, while waiting at a crosswalk, squinting at the oncoming traffic and studying the difference intensities of light coming off of car headlights. I was trying to figure out which headlights were LEDs and which ones were incandescents. I missed my signal to cross and had to wait for the next light change because of my musings.

My musings were inspired by a 90-minute walk through a hilly region of the city led by Robin Marks. Robin, a biochemist, science journalist and former science tinkerer at the Exploratorium, started Discovery Street Tours this past July. The website describes the tours as “more than just a walking tour. It’s an urban investigation of the science under your feet, in your food, and in your life. You’ll demo the science for yourself with hands-on activities, eat some tasty treats, and meet other folks like yourself—curious, active, and a little beyond the ordinary.”

Science got festive on the night of Sunday, December 11th as 18 of us, bundled against the cold and misting fog headed up 20th Street for the The Science of (Holiday) Light preview tour. Through the up-and-down mile and half route, we took frequent stops to admire holiday handiwork, discuss the history of holiday lights, view the different types and understand how our brains were taking in light signals.

My favorite part of the tour was when we stopped at a corner house strung with both LED and incandescent holiday lights. We were encouraged to look closely and notice the difference in both the quality and brightness of light. While incandescent bulbs use a filament to produce light and heat, LEDs (light emitting diodes) are lower energy semi-conducters. LEDs shoot out light in a straight line. After learning this, I was able to identify the LED string of lights not only by the light but the crystal cut bulbs around the light that enabled the straight line of light to be refracted — making the iconic twinkling glow associated with holiday lights.

As a nerd herder and being generally inquisitive about science, this was a very satisfying tour. I was able to ramble through the city taking in wonderful panoramic scenes in one instance and then turn around and look closer at the mundane with awe at how I was seeing it with new insight and understanding. My fellow tour-goers raised other questions about light and color, as our curiosity was further sparked by what we were seeing and learning. One conversation that got started involved pollinators; which insects and birds are attracted to the red over white flowers, and the effects the visible spectrum they see have on how they pollinate species of flowers.

As this was a preview, the inquisitive can still put science in their step. Robin will be leading The Science of (Holiday) Light tour several more times in December, including Christmas Eve and the evening of Christmas Day. Tours start at 6:30pm and all the dates, more details and booking information can be found online.

‘Tis The Season for the Science of Holiday Lights 15 December,2011Cat

  • Led string lights should never be used outdoors, why? Because the leds are made with wire that corrodes in water, it rust to nothing, I have plenty of pictures to show this corrosion. If you see yellowing of the light, that is corrosion, the end is near. Do not believe what the box state, do not use led Christmas lights outdoors.



Cathleen (Cat) is the former Special Projects Manager at California Academy of Sciences and worked in the public programs division.
Before working at the Academy, Cat got her start as an intern at Lindsay Wildlife Museum for four years and worked with animals ranging from snakes and hawks to foxes and bobcats. She has a deep curiosity about the natural world and native California wildlife.

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