A bit less than two decades ago, when I was still living with other (post-graduate) students we got a flyer which announced a low price for Compact Fluorescent Lighting compatible with our rented house. We went into the living room where there was a whiteboard, and worked out the TCO of these more efficient lamps over their lifetime compared to just the ongoing cost of our incandescents (since we had these already we didn't need a total cost).

We then immediately set out to purchase an entire house full of CFLs. They were still going years later when we split up and each took our share, I still have one somewhere, maybe in my living room.