Do dimmable ballast still using pulling full power even after dimmed?

I read that dimmable ballast still pull full power out of the outlit even if you have it on a dimmed setting, the lower power only goes to the bulb but the ballast is still pulling 100% power.

I am interested in this ballast http://solis-tek.com/digital-ballasts/solistek-400-digital-ballast.html

Says
"400W Dimmable Digital Ballast 120/240v Multi-Wattage, Multi-Voltage,Dimmable - 3.75A @120v - 1.87A @240v"
Which is
3.75a @ 120v = 450watts

I want to run this ballast with a 250 watt hps bulb, it doesn't give a amperage at 250w setting.

Anyone have experience with dimmable ballasts?

You ONLY use a 400 watt bulb with that ballast. Even dimmed.

To get amps you divide 250 watt by the voltage 120 = 2.08 amps. But the bigger question is, will the 250watt bulb blow up if plugged into a 400 watt ballast.

SnapsProvolone said:

You ONLY use a 400 watt bulb with that ballast. Even dimmed.

Click to expand...

Really lame I had my eye on that ballast for the dimmablity 250w, 400w and price.

I was hoping to find a ballast with a 250w and a 400w setting. I plan on using 250w hps during the summer.

A ballast driving a bulb will waste some power in the process thus the extra 50 watts. Nameplate is correct. Doing math of 250/120 doesn't account for ballast efficiency factor.

JCave said:

Really lame I had my eye on that ballast for the dimmablity and price.

I was hoping to find a ballast with a 250w and a 400w setting. I plan on using 250w hps during the summer.

Click to expand...

Just turn the knob down to lower setting and no bulb change required.