Purkinje and Goodnight Moon

Blog Vol 7.7. Purkinje and Goodnight Moon.

I confess I am a nerd, a Nerd on Sight, a play on the name of the franchised IT company called Nerds on Site, who just happens to write blogs all about eyes, sight, and everything even remotely connected.

No surprise, that as a father reading books to his children, I noticed right away that the popular children’s book, Goodnight Moon, is a fine application of the Purkinje Effect.  Published in 1947 by Margaret Wise Brown, the words and cadence are brilliant, but it is the pictures: their sequencing and subtle changes that get me.

The illustrator, Clement Hurd, who trained in Paris with Fernand Léger, was fully aware of how our eyes perceive light in varying conditions, a phenomenon called the Purkinje Effect. 

When we shift from photopic (bright light, light-adapted eyes, cone receptors) to scotopic (dimmer lighting, dark-adapted eyes, rod receptors), our perception changes. The peak sensitivity of the rods is 505 nanometres, a hue of blue, while the cones peak out at 555 nanometres. When the sun starts to go down, our eyes shift from daytime to nighttime vision, which is why seeing at dusk is so difficult.  The bright reds of daytime become more and more muted until they finally become gray-brown, while the cooler greens and blues pop as we acclimatize to less light. The Purkinje Effect.

Clement Hurd studied physiology, perception, and colour, and applied it to the book. As bedtime approaches and the lighting slowly dims, the colours change and we experience the coming of night, of bedtime. It really does work, though in Goodnight Moon the effect is more pronounced in the paper copy than the board book. Not surprisingly, this shift occurs quicker when you are young and slower as you age.   

Take time out to read to your children (grandchildren, nieces, nephews...). There are so many beautiful picture books to enjoy.  I have been enjoying  The Knight Owl books by Christopher Denise.



‘til next week,

 the good doctor