While it is definitely true that original power drops were due to lower lumens, few things:

- reflective housing is super inefficient (~70% losses on the bounced light off typical material, at the top end expensive stuff still ~23%), still better than just losing the light upwards but not as many lumens on the road as a lab test would show

- Today LEDs are more efficient than sodium

Some math: 100W HPS cobra head lamp prdouces 9.5k lumens, including ballast it draws ~133W from the wall. Lab test shows about 70% of the lamp's light leaves the fixture (with the rest being lost in the housing) leading to ~7k lumens exiting. Roughly 53 lm/W.

LED cobra head lamps get like ~125 lm/W on the low end + fade much more slowly than sodium