Besides lighting and other factors one thing that will make a difference is whose White Widow you are growing.
Most are knockoffs of the original so most are genetically different not only from the original but also from each other.
What one person may very well yield under the same growing conditions as someone else could very a fair bit just due to whose White Widow was grown by each person.
Black Label Seeds White Widow says: Yield (Dried grams per square meter in a Sea of Green): 325-425
De Sjamaans White Widow says: Indoor Yield: up to 500 grams per m2
Flying Dutchmans White Widow says: Yield: 150 gr.
Green House Seeds White Widow says: Yield (Indoors): 350 to 450 gr/sqm.
High Quality Seeds White Widow says:Yield (Dried grams per square meter in a Sea of Green): 325-425
Nirvanas White Widow Says: Production square meters indoors: 450 grams
Most of the time a yield is figured for a 600-watt HID lighting system so for anything less than that you can deduct part of the yield.