Difference between HQI, EYE, standard, and electric ballasts

[EmilyB]

How does that compare/or what is the difference to the Hamilton ballast which I am running (175w). It certainly does a fine job with the Ushios...on that tank? :?

ELECTRONIC METAL HALIDE 250 WATT BALLAST

Cool operating, silent & energy saving. Potted, moisture resistant ballast which provides reduced lamp flicker and consistent lumen output. UL approved. Works with all 250 Watt lamps. Works with all 250 Watt HQI double-ended. 8 1/2"L x 3 1/2"W x 2 1/8"H