Help! - completely confused

[mikemeister_admin]

Hi, - slightly off topic, but somebody may be able to help!

I've been playing with colour and I just do not understand what is going happening.

This is the baby .psd (245K) I've been playing with.
http://www.broadhurst-family.co.uk/CurveMeister/ColourExperiment.psd

I made it by creating a gradient spectum horizontally and then created a Soft Light layer above it where I vertically drew a black>white gradient (to create some tone contrast).

When I look at the colours in the info palette the L channel changes as I move vertically (as I would expect) - but if I convert this to rgb (no flatten) it does not change at all, but if I flatten it behaves the same.  What is going on?

I would also have expected more variation when applying the Soft Light layer.

[-default]

Definitely strange.  When I then un-flatten the RGB image, the Lightness value changes, more or less as expected.

I don't have an explanation, but it is true that the Soft Light calculation is probably performed entirely different for Lab mode than for RGB.  I've seen other weirdnesses that are due to the fact that Lab can represent colors that are not possible in RGB.

This an interesting problem that I don't have an explanation for.