400w MH to 250w MH - Big temperature difference?

[Todd]

Originally Posted by fkshiu

I think if you go from a 400W "HQI" down to a 250W electronic you will notice a difference in heat output because actual consumption will be halved from around 500W to 250W. However, if you're using, say, a 400W electronic ballast and go to a 250W HQI (M80) then you will hardly be using any less electricity and there will be no difference in heat.

When I went from magnetic 175W (M57) ballasts to 250W HQI (M80) my tank temps in the summer shot up quite a bit..

I'd be going from "hqi" which I understand to be a magnetic ballast (correct?) to a electronic (digital) ballast. It looks like everyone has a 50 / 50 opionion of if this will result in a change in temperature. What about electicity usage - Can I just simply figure out how many kWh this will result in saving and find out my power savings that way? Or is it not quite so simple.

I figured it would be this: [(800 w - 500 w) / 1000] x 6 hours per day x 7 days a week x 52 = 655.2 kWh

This would mean a 54$ savings in one year in electricity (based on BC hydros teir two rate). Unless there is a even larger difference in the electricity savings due the different ballasts being more efficient.

Any thoughts on this?