Is the "600W" light actually 600 Watts, or "600 watt equivalent" which is common with CFL and LEDs?
I recently bought a "1200W equivalent" LED light fixture which the fine print says consumes ~200-250W power. It was $90 on amazon. Yours is likely similar if it is LED. A true 600 watts-consumed LED fixture would likely cost $300+ and I've never actually seen one rated above 1500-watt-equivalent
I don't have any citrus under mine yet, only my wife's cooking herbs and a couple random seedlings I had extras of - lychee and ice cream bean. They are growing well under the light, but it is too early for me to tell how they compare to the same seedlings in my greenhouse under only natural light.
I have my light running 16hrs a day on a timer, it is in my basement which is around 65F all year. The light doesn't create enough heat to notice as it is in a wide open area. 200W 16hrs/day is under ten bucks a month in power cost
200Watts = 0.2 kilowatt-hours
power is ~10c kilowatt-hour
30 days a month, 16hrs a day
.200 * .10 * 30 * 16
$9.60
Oh yes, its claimed to be around 124w consumption, although comments have said it consumes more around the 200w at full blast. So far running it 12 hours at night I have seen substantial growth from my seedlings! I am happy with the light overall. But that's not bad in power price either, although I do have a fan going, 2 germination mats, and another LED for my seedlings. Either way, all work great!