Changing just of your bulbs to an energy saving one could save around 47 kg CO2 per bulb (see here for full calculation and assumptions).
The CO2 values in the slider have been averaged over a month, and split equally over the four data points, calculated as follows:
Q. How many lights in your home have low energy bulbs?
Endpoints:
None = 0 kg
All - (47 kg x 20 bulbs) / (12 months) = 78.33 kg CO2
Midpoints:
Some - (78.33) x (1/3) = 26.11 kg CO2
Most - (78.33) x (2/3) = 52.22 kg CO2
