I can't help but ask this because I feel there's a lot of controversy over LED lights being not as powerful as HID lights. Is there a measurable difference between a 1000 watt LED light and a 1000 watt HPS?
yes . depending on the brand . lets say it will take 2000 to 2500 watts from led to make the same amount of light . or foot print as a 1000 hps .. this is my opinion. the led most of them are rated stupid . so if you had a 2000 watt led its only pulling 1000 watts . buy hps there is no guess work it will grow the best brands do matter as much with hps and you can start up for about 100 to 500 . and for led start up is going to cost 300 to 3000 . if you really want to go led these are cheap priced led with good reviews . mars hydro . and meizhi . look at them on ebay . i used the meizhi it worked just as good as a mh light in veg but the yield was less then hps but the quality was high . hps is still the king right now my opinion . if your serious about led you should look into cobs people swear there better or just as good as hps but the start up is 5 times as much as led and hps .
Assuming your 1000w LED actually pulls 1000w, then there would not be a measurable difference in light output, but there would be a significant difference in cost. I have a 650w NextLight Mega and I would put it up against any 1000w HPS.
Watt for watt of electricity used, LEDs are much more powerful than HID. Here's a quote (possibly biased, but still convincing) from 5 Truths About Growing Bigger Yields With LED vs. HPS "HPS lights have been associated with high yields for a long time. But, there’s a reason why some of the largest commercial grow operations have made the switch to LED. A 600w HPS light can produce up to 150 to 300 grams in optimal grow environments, which is 0.5 grams per watt or less. LEDs, however, can produce as high as 1 to 1.5 grams per watt. All the while, LEDs use less energy to produce the equivalent HPS wattage.For example, Kind’s K3L600 lights have an actual wattage of 320. Yet, they produce an equal light quality to that of a 600-watt HPS." Not to mention the electrical savings on heat removal.
There are several factors involved in measuring a light's performance. Lumens is an older scale based on how bright a light looks to the human eye. There is a newer scale based on the spectrum of light that grows plants the best. It's called the P.A.R. scale. Photosynthetically active radiation - Wikipedia The brightness of the light is only one factor in how well it will grow. Plants use specific spectrums of light more then others. If your light matches this curve that grows plants best it doesn't have to be as bright to be more efficient at growing. There's also factors in how well they reach and how much heat they make. LED's have undergone an evolution the last 5 years. The efficiencies have went way up in even the last 1-2 years where the newest led's have 30-50% or better performance compared to led's from just a short time ago depending on what you're comparing. Many of the lights on the market are 4 year old or older designs. Most never really lived up to the claims made by their advertisements. The lights on the market the last 2 years that are mostly DIY have set new standards for growing efficiency. I've seen close to 2 grams per watt with these newer lights. I mostly agree with bk but he's underestimating what HPS can do. Talented growers can get over a pound from a 600 watt hps and the right strains with hydroponics. That's still well under 1 gram per watt. Most hps growers never make it there. You will hear growers bragging about 2 pounds per 1000 watt light. That's close to 1 gram per watt but many are using 1150 watt gavitas when they do that so the watt per gram figure is worse then it sounds. It sounds funny to brag about .8grams/watt as a seasoned pro/commercial grower when 3 crop rookie growers are now doing that with cheap led panels.