Lumen is the SI derived unit measuring how much light you are getting from a bulb.
While watt is a unit of power measuring the amount of energy an item needs to function.
Formula to convert W to lm.
Converting these units is like measuring how well a light source converts energy into light.
For a 100 W incandescent bulb produces about 1,600 lumens, for an efficiency of 1,600/100 = 16 lumens per watt.
A halogen bulb consumes only 72 watts for the same amount of brightness, making its efficiency to be 22 lumens per watt.
A CFL bulb consumes 26 W making its efficiency to be 61 lumens per watt.
LED bulbs, which are the most efficient, consume only 22 watts for an efficiency of 73 lumens per watt.
Convert 75 watts incandescent bulb if its efficiency is 15 watts per lumen and you asked to convert the energy to lumens per watt.
= 75 x 15
= 800 lumens.