Exposure ramping is new to me and I like to try new things, so I've been mulling it over. The idea is that you shoot a sequence of shots and change the exposure value to equalise all frames so they can be animated together smoothly without getting darker too fast.
Well, I looked everywhere on the net for a measurement of light reduction during sunset and came up with nothing :) After a think, I realised that you don't really need to know as you can just shoot in A priority and let the shutter sort itself out. Except!!! when you want to keep the shutter speed the same and adjust the ISO to prevent blur ;) So, tonight, I sat at the Bill of Portland and measured the EV of the fading light for around 90 minutes.
It seems the light fades almost exponentially just before sunset and then slows to linear thereafter. The sun did go behind very light cloud at around 15.55, but it's not shown in the results much. May not be very scientific, but if you ever wondered how light fades during sunset, here's my effort ;)