How to compare the brightness of low energy bulbs to normal bulbs?
A low energy bulb has a much lower wattage because it uses less electricity. In general the light output from a low energy bulb is equivalent to a wattage 4-5 times higher in an incandescent bulb. This is effected by the size and shape of the low energy bulb.
e.g. A 9w low energy bulb will generate approximately as much light as a 40w standard bulb. A 15w low energy bulb is roughly equivalent to a 75w normal bulb.