To produce a light of 80 lm one could use a 1 W LED lamp or a
kerosene lamp which consumes 0.05 l of fuel in 1 h. Even consider-
ing a very low Kerosene price of
€
0.3/L, this lamp would spend 1.5
c
€
each hour, i.e.
€
1.8 in a month if lighted for 4 h daily. On the
other hand, the 1 W LED lamp would consumer just 0.12 kW h of