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Treebeard's Stumper Answer
24 January 2003

Sunbeams and God Light

We call it God light or sunbeams. The official name is crepuscular rays. That's a harsh name for those beautiful lines of light that sometimes radiate across the sky from the sun hidden behind a cloud, often at twilight. Sunlight travels 93 million miles to Earth in nearly parallel rays, so why do these visible light beams suddenly seem to fan out across the sky above us? The sky is full of light, so why don't we see sunbeams all the time? I always try to photograph these light rays, but my photos rarely capture them. What is the best exposure setting for my semi-auto digital camera?


Santa Ynez Mountains, 26 August 1999

Santa Ynez Valley, 19 December 2002

Surf Beach, 29 November 2001

Knapp Castle sunset, 30 August 2002

San Marcos Pass woodland, 23 July 1998

Are the last two photos the same effect or something different? I didn't notice the sunbeams when I took these pictures, and the photos where a pleasant surprise. Where else do you see sunbeams?

I should explain that my Olympus 2040Z digital camera has fully manual exposure and focus control, along with aperture- and shutter-priority modes. That was one reason why I bought it. But I usually use the "program auto" setting. This still gives me exposure control because there is a target in the viewfinder that I can position anywhere in the scene before I press the shutter button halfway down to lock that exposure and focus. Then I can move the camera to frame my shot before pressing the button all the way down to actually take the picture with the remembered exposure. It makes a big difference where I point my camera when I lock the exposure. I can also push buttons to deliberately under- or over-expose. This works much like my beloved (long ago stolen) Nikon FTn "needle match" camera. I usually take lots of photos and hope for a keeper, and digital shots are free. I always forget what I did, so what's the best way to deliberately get a great photo of sunbeams? Where should I point my camera when I lock the exposure?

Another stumper: I've been looking for paintings with crepuscular rays. My first thought was Medieval or Renaissance religious art, but I haven't found a great example. Help!

Beautiful sunbeams or crepuscular rays depend on several factors. There must be a cloud or mountain to make shadow rays to separate light and dark. There must be small particles like dust or water droplets in the air to scatter the sunlight and make it visible, like headlights in fog. A dark storm cloud backdrop helps add contrast. Parallel light rays spread across the sky by simple perspective just like train tracks converge in the distance. That's really not a stumper, and it's not the light but the not-light shadows that makes sunbeams visible. This seems very Taoist!


I fell behind on my stumpers, but I'm getting back to this one after nearly a month thinking about other stumpers, not to mention family and school. I think my short answer is just right. We see exactly what we should. We see the light rays because of the shadows, and we see the shadow rays because of the light. Sometimes the shadows dominate like my first photo above, but it always takes light and dark to make both visible. The symbol of Taoism is the yin yang, where each fish outlines the other.

I teach one- and two-point perspective drawing in my elective drafting classes at DMS. I don't try to explain the details except for advanced topics like perspective circles and arches. It's enough to show the kids how it works. The classic example is the way railroad tracks converge to a distant vanishing point like this train trestle across the Santa Ynez River mouth near Lompoc, California. I added a few more photos that show how parallel lines converge (or spread) by perspective. By following the "parallel lines" in each photo, you can find the vanishing point, though it may be out of the picture frame. Crepuscular rays converge and diverge in the same way, and you can also follow the lines in my photos above.


Sunbeam photos make a more interesting stumper. I'm a sucker for backlighting - shooting into the light behind the subject - but I sure can't predict the results. Part of the problem is that my digital camera is more contrasty than my old film camera, so it can't show as much range between the brightest and darkest parts of the photo. But it's free to take lots of photos and hope for a good one. I think the key is to underexpose.

Light rays in photos are another matter. I have many photos with the same pattern of light rays as the two bottom photos above. I'm sure these rays are an artifact caused by the pentagonal camera diaphram that controls my f-stop.

Here I started with the San Marcos Pass woodland photo above. Then I used Paint Shop Pro to cut out the pentagon-shape from a photo of jet contrails shot into the sun. Then then I cut out those beautiful sunbeams behind Julie at Knapp Castle. Everything lines up perfectly when rotated and pasted together.

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I'm sure these beautiful sunbeams are artifacts of my camera diaphram and me standing in just the right place, but I still like them! But what about these photos that have way too many points? And what are they photos of?


The left photo is looking up through a flowering yucca stalk while standing in just the right place. The other is the solar weenie (as my students named it). It's a thin black plastic bag that you blow up and leave in the sun to warm up and float away. It really did!

Another stumper is why the physical clouds sometimes line up with the sun, radiating away in perspective lines across the sky. I've seen this many times, though I don't have many photos to back it up. Here's a shot of my DMS Hike Club kids at Knapp Castle looking into the setting sun. Are those radiating cirrus clouds just a coincidence?


I've found many names for crepuscular rays on the Web including: sunbeams, light rays, light beams, God Light, God's Light, Jesus Light, Rays of Buddha, Buddha's Fingers, Ropes of Maui, Jacob's Ladder (?), and the Sun Drawing Water. Lots of names, but I still haven't found many classic paintings. Here are two details. (Click for more.)

Francesco del Cossa
Saint Lucy, c.1470
Pieter Lastman
Abraham on the Way to Canaan, 1614

Here are some Web links for more research on these stumpers.

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