Hmm. Unfortunately HWKE, there is no hard and fast rule or method of calculating exact equivalents.
I have in my hand at the moment a Philips 12 Years Energy Saver bulb, code 544742xx. This particular bulb uses 20 Watts of energy and is equivalent to 100 Watts.
It seems to depend on the construction and shape of the bulb and no doubt your example differs in shape from the one I have.
hairygrape:
I don't doubt that you are correct. I based my answer on the ones I have been buying and haven't seen any other equivalents. Although I have bought several different types and they have said the same each time, I foolishly didn't consider different design capabilities from different manufacturers. I wouldn't have thought that there would be a great deal of difference though.
I have no doubt that there will be others in the future claiming less power consumption and greater light output.
My wife claims that they are all dull as well so I'd better not let her see your posting.
I meant to say 11 watt is the equivalent of 60 watt ordinary (of the type I buy). I didn't notice I'd typed a 9 instead of a 0.
I buy all my light bulbs and batteries at suprem-imports.co.uk they say that the general rule of tumb is a multiplication factor of 5. If you have 100w bulb you will need a 20w low energy version, 60w will be approx 11w.