This photo of the
In the late afternoon as the sun slips lower in the west the eucalyptus gums and bush on the eastern river bank light up. There is a small window of time when the colours intensify and the greens of the trees and the shadows they cast, become so green they are almost surreal.
This phenomena occurring at dusk is called the Purkinje effect. It happens when the light sensitive systems in our retinas work in tandem. We have two sets of light receptors, the cones and the rods. They usually work independently of each other; the cones in the day and the rods at night.
The phototropic cones are colour sensitive while the scotopic rods do not distinguish colour but respond best to blue and green light. That’s why at night when the rods function we are virtually colour blind.
At dusk as the intensity of the sunlight dims there is a transition between the cone and rod systems. The rods start to take over our vision before the colour disappears completely and then for a brief time the two different receptors work together producing this vivid bright green effect.
While my photograph doesn’t capture the intense green light on the trees it does show how they become beautifully illuminated. In this photo there are also storm clouds circling overhead providing added contrast. Some stray cormorants are making a tardy homecoming to roost in the gum trees with the rest of their flock.
I think that today I will give thanks for the wonders of green with this poem by e.e.cummings: