A 600w HPS has a quantum efficiency of ~1.5umols per watt in comparison your LED barlight doubles that.
Then, there's 3 other major differences, the HPS light has a much better penetration or leaf transmittance and its light recipe additionally causes longer internodes and that alltogether makes the plant gather more light as a whole. Also the plant's oxygen evolution rate (a direct measurement of PS2 photochemistry) will be higher.
It's because the HPS delivers a complete package of yellow/orange light complimented by very little blue, farred and much heat (IR).
In stark contrast that LED has much blue, high red but only very little farred and no IR, all things considered creates a stocky short plant with leaves upon leaves shadowing one another.
If you ever think about improving that spectrum think about a farred extension kit on a separate timer that will cut down your veg-time by weeks, and give a sleep initiation, too.
But the highest priority right now I see is to dial in the temperature right. An IR heater is best because it will heat up the leaves and not the air (which is mostly vented out anyway). Or you can manage it somehow to heat up the air before the intake.
Another method oftentimes used is to blow down the air from above the LED and have both a cooling effect (= diodes more efficient) and a plant benefit. Some LED growers even reverse the airflow and vent out from below to get that effect
www.thcfarmer.com
