“In photometry, luminous flux … is the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.”
http://en.wikipedia.org/wiki/Luminous_flux

Luminous flux accounts for the relativity of perception, in the same way that optimism and pessimism can flux from one to the other.

I think of optimism and pessimism as inseparable poles, whose ambi-valent pulls are equally strong, producing a productive state of dialectical tension. But my latest work is premised on the idea that hope is rare and requires willpower, while pessimism is abundant and passive.

According to Adam Cohen, in his review of Joshua Foa Dienstag’s Pessimism: Philosophy, Ethic, Spirit (nytimes.com, August 28, 2006), “Pessimism is not, as is commonly thought, about being depressed or misanthropic, and it does not hold that humanity is headed for disaster. It simply doubts the most basic liberal principle: that applying human reasoning to the world’s problems will have a positive effect.”

So it occurred to me that the metaphor of light and dark for optimism and pessimism lends itself to the idea that hope is rare and pessimism is abundant. Because light, which often represents hope, is rare — especially when you consider that only visible light connotes hope, while the rest of the electromagnetic spectrum bounces around and through us, constantly and imperceptibly.

Even the view that hope is rare may seem pessimistic. But rarity suggests a thing that becomes valued, cultivated, appreciated.