1. The replacement of LED lamps with incandescent lamps is not simply measured by the number of W. For example, the same 10W LED lamp, some 800 lumens, and some more than 900 lumens. This is to understand the concept of "light efficiency", that is, how much lumens each W emits.
2. If the 40W incandescent lamp's luminous flux is 400 lumens, then according to the LED lamp's luminous efficiency of 80 lumens/watt, then the LED should be 400/80=5W.
LED Lights Common Energy Saving Lamps Incandescent
1W 3W 15W
3W 8W 40W
5W 15W 60W
7W 20W 85W
12W 35W 120W