THE ELECTRICITY EFFICIENCY FEED-IN-TARIFF

The details are in an article on ,Bishop Hill Blog, though having read the blog article as well as looking at the linked article on Business Green, I am still unclear, along with most of the commenters beneath the BH article. I can perfectly well understand what a feed-in-tariff is when applied to a consumer generating electricity and feeding it into the grid, but this seems to apply not to electricity generated, but electricity "saved" by the consumer purchasing some more efficient item such as low-energy light bulbs. What is not clear is exactly how the "saving" is calculated. Is it done by some formula, in which case there may not be any actual saving at all? The consumer might, for example, decide to leave all his lights on for much longer. The "saving" could be calculated by looking at his actual usage, but he could be saving electricity because, for example, his washing machine has packed up and he is doing his washing at a friend's house. Can anyone throw any light on this, or is it simply as daft as I think?