First assumption is that you will throw away the CFL instead of recycling it. I am not going to do that and most likely neither are you. Let say you did. The biggest difference is that the mercury would be in a landfill and not in the air. Then after it rain it gets into the water way and …

While googling I found a great mercury coal resource for Indiana. I mean perfectly wonderful. The average amount of mercury in Indiana Coal is 0.11 mg/kg.

How much energy is in one kg of coal? According to Wikipedia. 2kW hours / kg.

If a CFL lasts 10,000 hours and it is a 23 Watt (100W incandescent), you would have to burn;

CFL >> 10,000 x 23 Watts = 230 kW hours

Incandescent >> 10,000 x 100 = 1000 kW hours

Difference of >> 770 kW hours or 770 kW hours / 2 kW per kg x 0.11 mg

42 mg of mercury

That seems to jive with what ours have calculated. Basically, it is better to use a CFL for reducing mercury then to stick with an incandescent. It is even better when you recycle the spent CFL.