The power of light - comparing apples with apples?

Agreed but I have a mate who 'needs' explanations but doesn't have the background experience or knowledge and that fifty word explanation looks logical if you don't know and will save me sheets and sheets of paper and the loss of already thinning hair! I tried explaining colour theory to him...

I can understand the motivation, but it is a bit like explaining the evolution to mankind as '...rib from Adam and created Eve'. Nowhere close to reality, and not even a reasonable and simple explanation of what occurred. (After all, Adam would have had to start with an odd number of ribs!)

Well if you are not constrained by some sort of factual underpinning, just get in there and mix it up.

Just tell him to divide the Watt-sec rating of the flash power pack by 1000 and that will give the approximate equivalent in Watts of a tungsten light.

When facts no longer ground, have meaning, or need to integrate with the rational and physical world, things should be easy. Use your imagination.

Sounds sort of like science fiction. A sprinkle of science terminology mixed into a wash of words that humans somehow have an affinity for.

Enjoy! Lon

Perhaps a little explanation is in order. I certainly wouldn't make that kind of explanation in these circles, if I don't know, here I might ask or simply read.

But, I learned most of the relevent material thirty to forty years ago, and once you know how and why the theory becomes less important than using and doing. However, my mate discovered the joy of photography two years ago at the age of 67 and is really going into digital in a big way. And to be honest I've grown tired of having a couple of hours spent arguing about the technology when I know full well that either he hasn't understood or will have forgotten and still go away and be a happy snapper.

But this conversation brought two topics to mind: are there any published characteristic curves for digital cameras, do digital sensors suffer from reciprocity failure?

Reciprocity failure is not a problem with digital cameras, but long exposures tend to generate more digital noise.