Thursday, September 22, 2011

Brown polarized sunglasses are great!

I used to wonder why someone would want brown or amber sunglasses. Why add a colour cast to everything? Now I know. The colour:
  • decreases sky brightness, equalizing the overall brightness of the scene
  • removes glare, while still making the scene appear bright in a pleasant way
  • accentuates green foliage and various other colours
  • makes hazy days seem sunnier
  • helps decrease glare when driving toward the sun
(Blue-grey sunglasses are the opposite. They dim things relative to the sky, they make foliage look worse, and they aren't very effective at decreasing glare. I don't want those ever again.)

Polarization is also an important enhancement. It:
  • decreases the intensity of annoying bright reflections from non-metallic surfaces, such as reflections from the paint of cars or bodies of water
  • increases colour saturation by removing reflections (Foliage reflects a lot of light, and looks much greener when that reflection is blocked. Water surfaces also reflect light, and when that reflection is blocked, the colours of the water itself stand out.)
  • makes the sky darker and bluer in certain directions, making clouds stand out and helping equalize the overall brightness of the scene
The only downside of polarization is that the intensity of the effect depends on the orientation of the glasses.  It is most optimal when the sun is highest in the sky. Near sunset, the sunglasses need to be turned sideways to create a strong effect. Sometimes, I thought about creating electronically controlled polarized sunglasses using camera filters and a microcontroller.

When buying polarized sunglasses, it's important to check whether the effect works well. Turn the glasses and block some reflections. Cheap glasses may not be able to block reflections very much, or the blocked reflections may show a strong purple colour cast.

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