You are probably thinking of the work of Bill Norhaus. NPR have covered this https://www.npr.org/2014/05/02/309040279/in-4-000-years-one-thing-hasnt-changed-it

You are probably thinking of the work of Bill Norhaus. NPR have covered this https://www.npr.org/2014/05/02/309040279/in-4-000-years-one-thing-hasnt-changed-it-takes-time-to-buy-light?t=1658494560737 https://www.npr.org/2014/05/02/309040279/in-4-000-years-one-... The cost of light now is vastly cheaper than your estimate. When he did the research in the 1990s you could buy a days light with less than a minute of work. With modern LED lighting it is probably seconds.