Two nights ago I took a photo of the star Arcturus, using my Canon 70D camera with a 200mm zoom. The exposure time was 1.0 second, during which time I hand-held the camera and moved it during the shot. Here's the result.

The trace shows a massive number of variations (over 800!) of brightness and color. This is scintillation, better known as twinkling. Our eyes aren't able to see all these variations because (a) they're too dim, so we don't see the colors, and (b) they're too fast, so we see only the largest and slowest variations in brightness as twinkles.

The cause of these variations is atmospheric - the star itself is NOT twinkling! If you took a photo like this from the International Space Station, it would be a constantly bright, slightly orange line with no variations in color or brightness.

I'm very excited to be the current featured artist over at Light Painting Photography, Jason Page's great nexus for all things light painting. Jason worked with me to create a great interview, sprinkled with many of my photos and links back to here. Thanks, Jason! It's humbling to see my rather unique photography being showcased to such a creative crowd of people, and I hope that it stimulates some new ideas and techniques. I'm looking forward to seeing where this new endeavor takes me.

In case you weren't already convinced that most street lights are time-varying, here's proof. This is a shot I took of a small US city (I don't know which) from an airplane at night. I swept the camera while taking the shot, using a 1/10 second exposure time. As you can see, there are many lights and groups of lights which show strong periodic traces. Most of these lights are pressurized sodium street lights, which flash at 120 times per second (in the US).

I had to adjust the exposure and tone curve in Lightroom to compensate for the fact that a city at night isn't very bright as far as a camera's concerned; and when you sweep the camera, it's even dimmer.

Christmas is coming... and LED Christmas lights are appearing. Almost without exception, these LEDs flash at 60 Hz (in the US, 50 Hz in Europe). The result: move the camera and you'll see the dashed-line trace of each LED. Here's an example...

Inspired by something I saw online, I decided to try reflecting an image in horizontal and vertical axes using Photoshop. Here's the result:

The original, non reflected image can be seen here.

I've made a cool discovery: cellphone cameras (and probably most cameras with a live display (sometimes called "live view") can be used to observe time-varying light sources.

Simply open the camera app and point the camera at the light source of interest, then rock the camera rapidly up and down so that the light source paints a trail on the screen. In most cases, you'll be able to see the trail breaking up into dashes or repeated images, showing that the light source is time-varying. It's not as good as eyeball- or mirror-jiggling (see my "How To See" page), but as a quick way to see if a light has time-varying behavior, it can be useful.

I've tested it so far on three cellphones: LG G4, Apple iPhone 6+ and Motorola Droid Mini. It helps to let the camera focus on the light source first before rocking the camera up and down.

I've just moved to the LG G4 phone, and was excited about its camera's manual mode. Tonight I had a chance to try it out. I photographed this restaurant, which has a line of white LEDs around its windows:

By using the camera's manual settings, I captured this image:

The time-varying behavior of these LEDs is very easy to see with the naked eye, and may well be one of the easiest subjects for vision jiggling.

To get this image, I selected the following settings:

• Manual focus (so that it would not be trying to focus while taking the shot)
• ISO 500 (to underexpose the image so that I get the lights, not the whole scene)
• 1/8 second (to capture for long enough to give me plenty of dashes in the traces)

The primary weakness with the G4's camera is that there's an appreciable delay between pressing the button and the shot being taken, and since you have to keep the camera moving it's unpredictable what you'll capture. The solution is to take several shots until you get what you want. Aside from that, though, and the lack of optical zoom (which isn't too much of a problem for this type of photography), the G4 makes a great pocket tool for the photographer of time-varying light sources. Highly recommended.

I'm ramping up on Twitter. Feel free to follow me: @TimeVaryLights . Enjoy!

This is a slightly cropped region of a photograph I took at Indianapolis airport in March 2015. It shows a long building with pressurized sodium lights along the front. The cool thing to note are the regions where the traces show strong diagonal patterns to the light and dark dashes. This is due to the fact that the electrical contractor who wired up the lights was fairly rigorous in following a 1 - 2 - 3 - 1 - 2 - 3 sequence when selecting which phase of the three-phase electrical supply each light should be connected to. This is a sensible approach as it balances the load nicely. And, for those who know how to see it, it makes a cool pattern!