Return on investment calculations link

im looking for a link to an in depth calculation of the roi of using cob led that accounts for hvac as well as electrical savings over the short term and drawn out over a few years i know i read it a while ago and have looked high and low for it, was hoping for someone to jump in with a link to the thread im talking about

fixed initial costs cob + running costs cob * x (months) = fixed initial costs hps + running costs hps * x

x = ROI in months