I estimate 35-36% for standard 600-1000W HPS and ~40% for the 1000W DE HPS, when the bulbs are brand new. Of course they cannot be compared directly, a 600W 35% efficient LED will grow a lot more bud than a 600W HPS. Just how great the difference is is a controversial topic.
@Greengenes707 did an excellent side by side of 600W Apache LED vs 1000W Hortilux HPS, using the same cutting, same air, same ferts etc. The yield was comparable. Those results are a very strong data point in my mind because GG is not bias, just a smart guy looking for results in his jars.
Also worth mentioning, the LED grown weed tested with higher cannabinoids and higher terpenes than the HPS samples. I estimate that Apache LED was in the low-mid 30s in terms of efficiency, so you can extrapolate what a 55% LED will do.