Lighting efficiency question - Dimmable, Selectable, or regular Ballast?

SO, I was shopping for a new light and ballast today, and had a question that even my very experienced "mentor" at the hydro shop couldn't answer very clearly. I am not on a very large scale. My grows are strictly for personal use - and I don't smoke huge quantities - 2 plants at a time keeps me supplied just fine.

The first HID light I chose for the small closet (4'x2') was 250 watts with an air-cooled hood. I am more than happy with the output, but am considering upgrading to either a 400 or 600 watt system for bigger yeild. He told me that's exactly what most growers go through- start small and want to keep on upping their game. So he recommended a 1000 Watt SELECTABLE ballast. You can set it to 400 watts and put a 400 watt bulb in there, or 600, or 1000. He also showed me a couple of dimmable ballasts, which led to my question:

If you take a 1000 watt bulb, and dim it down to say 400 watts, is it just as efficient as running a 400 watt ballast with a 400 watt bulb in it? We pondered this for a while, and both decided that some research was in order. I would think that you would get maximum efficiency and lumen output by just runnning a 400 watt ballast with a 400 watt bulb in it. That's exactly what it was designed for, and you're not cutting back power to a larger bulb to get down to the wattage you want. It just seems to me like you would lose something by dimming a bulb. Maybe I'm overthinking it. I think when I'm ready to make my next purchase, I will go with the "Selectable" ballast instead of the "dimmable" one. That way I still have the flexibility to change my power settings & bulbs, but I don't have to under-power a 1000 watter.

Are there any experienced growers / engineers / electricians that might have some input on this? My guess is that if there IS any difference, it would probably be very minimal - but still - if I'm spending my hard-earned cash, I want the most efficient & highest lumen output available.

MDEVA said:

If you take a 1000 watt bulb, and dim it down to say 400 watts, is it just as efficient as running a 400 watt ballast with a 400 watt bulb in it? .

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Nope. Your best bet is running your ballast on full blast. 400w ballast with 400w bulb will do you better.
The dimmable ballasts are good if you are introducing seeds or clones into an HPS environment and dont want to fry them. Or to dial back the heat on an abnormally hot day. You don't want to make a habit of running your ballast in a dimmed mode, though.

Thanks for confirming that! That was my suspicion, but with all the people I know who are doing it, I kind of doubted myself. I may go with one of the newer Lumatek selectable ballasts though. They seem like the way to go. Definitely better than dimming down a normal ballast to the power I need. With those, you can actually select 400 watts and put a 400 watt bulb in them. Nice that they're flexible, ranging from 1000 watts down to 400.

I'd like to see the white papers on those "selectable" ballasts. If they manage >96% efficiency at the lower wattage settings, as they claim their dimmable ballasts do at full output, then I'd be interested to try one. Maybe after the "new toy" prices come down to a more reasonable level. It would certainly be useful in a single-lamp setup...

Be advised with any type of HID dimming systems the lamps are susceptible to color shift and shortened life. HID lamps should be started in the highest wattage setting then dimmed down so as to remove any carbon buildup on the arctube. There is alot of information on how controls for a variety of HID lighting systems @

http://www.isienergycontrols.com/wp-content/uploads/2011/05/NEMALSD14-2010Guidelines.pdf

Peragro said:

I'd like to see the white papers on those "selectable" ballasts. If they manage >96% efficiency at the lower wattage settings, as they claim their dimmable ballasts do at full output, then I'd be interested to try one. Maybe after the "new toy" prices come down to a more reasonable level. It would certainly be useful in a single-lamp setup...

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Would that apply to Lumatek's newer selectable ballasts also Chazbolin?

Clown Baby said:

Nope. Your best bet is running your ballast on full blast. 400w ballast with 400w bulb will do you better.
The dimmable ballasts are good if you are introducing seeds or clones into an HPS environment and dont want to fry them. Or to dial back the heat on an abnormally hot day. You don't want to make a habit of running your ballast in a dimmed mode, though.

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sorry, but i think this is utter BS. do you have any facts that your base your opinion on? i have a dimmable lumatek 400w ballast right here and measured with a belkin power meter in 250w mode it pulls 270w TOTAL with a osram plantastar 400w bulb (290w total in 250w-SL mode), which is very effficient, especially compared with magnetic ballasts. do you want to tell me that a 250w ballast with a 250w bulb would pull significantly less than 20w (ballast only)? i highly doubt that. also, according to philips and osram papers it is no problem to dim HPS bulbs. you should never dim MH bulbs though, because the light spectrum might change.

@assyrix - that's pretty interesting. So a MH bulb shouldn't be dimmed huh? I'd never heard that... but then again, I'm just now starting to look into a new HID setup. Good to know.