On the advice of Pablo during the Blender Today Live, I post my question in this section.
It’s apparently a simple question but did not find a clear answer : what the meaning of Watt for the light power in Blender ?
Here : Why Watt as light value? or here : Physically correct lighting - #3 by CarlG - Lighting and Rendering - Blender Artists Community
it says that we have to multiply power light by 683 to convert it in Lumen but I think it not works because 1000W in Blender (default point lamp power in Blender) cannot be 683000 Lumens (or even 200000 Lumens for a supposed white color value instead of green).
Maybe the light power could be the electrical power of a bulb light ? It seems to be closer to reality but i’m not sure if it’s the right answer.