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robby21
04/29/2006, 03:02 PM
Hello :)
do you guys think that a 150w hqi at 6 inch from the surface of the water equal a 250w at 12 inch from the surface?

robsmith32
04/29/2006, 06:33 PM
if look at sanjays page, it doesn't show diff in height from surface.
but there are some bulb/ballast at 150 that outperform other combos at 250w.

bertoni
04/29/2006, 06:35 PM
That would depend also on the reflector. Sanjay's pages also have good reflector reviews.

robby21
04/30/2006, 06:09 AM
I mean if you use the same reflector and ballast of course

finrod2
04/30/2006, 08:59 AM
The inverse square law states that a light source twice the distance would need to be 4x the intensity to equal the original. At least thats what my astronomy books tell me.

bertoni
04/30/2006, 09:10 AM
That only applies to a point source, unfocused. A foxuses beam won't lose much intensity while it remains coherent, the "near field" effect, I think it's called.

So it depends on which reflector is used. Some focus better than others. The same ballast won't work for the two separate bulbs.

jman77
04/30/2006, 11:28 AM
I have a dual 250w HQI fixture over my 58g. As soon as it's time to change the bulbs i'm switching the ballasts, bulbs, and sockets to a 150w setup with 10k bulbs and lower the fixture closer to the water.

The 250's are really strong and give off a lot of bloody heat for something that is going to run 8 hours a day. And HQI’s use up more juice than what is stated…. A 150w uses around 200w and a 250 uses around 300.

bertoni
04/30/2006, 02:23 PM
The wattage rating for the bulb is for the bulb only. The ballast also wastes some energy as heat.

I'd be tempted to go with the Iwasaki 175 W bulbs in some ReefOptix or similar pendants. I have one over a 29g and like it a lot so far.