One persistent issue with night photography in Victoria is the red light cast on the sky when doing long exposures along our eastern shore. Head out to Cattle Point or Cadboro Bay on any given cloudy night and try an exposure of five seconds or more. The result is always a reddish sky.
Shooting north from Cattle Point in Oak Bay during a thunderstorm
As usual, I first blamed Oak Bay for the problem, assuming that street lights in that gross red spectrum must be at fault. It made sense at the time as I'd seen many a prairie city glowing sickly orange from far off when on late night road trips. Despite this, I still needed to apply some critical thought to my theory, as using Oak Bay council as a catch all for assigning blame doesn't always stand up to scientific scrutiny. My theory quickly fell apart when examining some shots taken nearby Esquimalt's ugly orange lights. The cobalt blue skies of my long exposures taken there convinced me that my early assumptions had to be way off, so I looked around for a better explanation. The red navigation lights on the large towers off to the north were considered, but despite the prominence that height gives them, the total lumen output would be small compared to other red light sources in the area.
Shooting south from Saxe Point, Esquimalt. Note the total lack of red glow.
So what else does our eastern shore have that the west doesn't? Higher property tax assessments, more Volvos, and way less pickup trucks, but none of those have much affect on visible light. It had to be something else. The biggest clue though, came from the west.
Sunsets are red for one reason. When a light source disappears over the horizon, the longer wavelengths of the red light can travel furthest, remaining visible long after the other colours fade. While there isn't any sunset in the east, there are two large light sources over the eastern horizon at night, Vancouver and Bellingham. Neither are visible from our eastern shore, but both are just over the horizon, and both put out huge amounts of light. It makes sense to me that all the red light cast by them is more than enough to be adding that annoying red tinge to our long exposures.
How does one get rid of this light pollution? Asking Vancouver to turn out the lights after 9pm is impractical. They drive bad enough over there without getting rid of the street lights. A cyan filter absorbs red light and may be useful. Desaturating reds in post processing is easy, although I find that this just makes for a grey photo. In other words, we are just stuck with it.
Australian photographer Gary Ayton explains all this in great detail on his website, which is one of the most informative I've found on a subject that really isn't covered enough. Light pollution is just a fact of life in night photography, but we can take some solace in the fact that we are pretty lucky in Victoria, one of the few capital cities where you can look up and see the stars at night. We also get to blame most of our light pollution on someone else (Vancouver). One more thing for us to feel superior about besides better beer, lower crime, cleaner air, less traffic, better WHL team, and so on, and so on.