Double-Ended Metal Halides (1 Viewer)

[Wildfire]

Okay, I've searched and searched and can't figure it out. WHY are Double-Ended bulbs different (other than the obvious) than "normal" bulbs? All I can think about is that the normal bulbs tend to droop from the socket towards the water. Do the double-ended bulbs not sag towards the water line? Are they brighter? Do they have a longer life-span?

Anyone help me out here? I am beginning my hood construction, and need to get the "final" peices... MH Ballasts and EndSockets (and the bulbs).

 

[AggieBrandon]

I have heard that the de bulbs are a lot brighter than mogul based bulbs. I think I read someone stating that the 250 de was as bright or brighter than a 400 watt screw in bulb.

Brandon

 

[Guest]

A 250w DE is almost as bright as a 400w mogul bulb.

The main difference is that the shape of the bulb allows them to design better reflectors which throw a lot more light into the tank. Also, if you run them on a true HQI ballast (instead of electronic), it overdrives the bulbs to > 300w so they are even brighter.

I use an IceCap ballast with mine, so they're not overdriven, but they are still very bright and hopefully the bulbs will last longer.

 

[dfimble]

Just curious, but how does the shape allow for better design of the reflector? I have a "Normal" one with a reflector and am not sure how the reflector could be any better with a double ended one.

As far as shape, are you refering to the bulk or how its mounted?

David

 

[Guest]

From Sanjay Joshi's test of DE fixtures (and a comparison with 400w bulbs):

Interestingly when comparing the total incident light over the 3X3, 2X2 and 1X1 areas there is only a slight decrease in total incident light, while the lamp power is decreased by 37%. Why is there such a disproportionate difference? One possible explanation could be that the 400W fixtures are not as efficient as the 250W DE fixtures – the small size of the DE lamp allows for better reflector design and allows more of the light to get out of the reflector. With the 400W systems, the larger size of the lamp envelope may be causing some of the light to reflect back into the lamp envelope.

This is just one theory offered and is by no means definitive. Probably everyone who compares 250w DE to 400w lamps (myself included) is using this article as the basis for the comparison.

The entire article is here:

http://www.advancedaquarist.com/issues/july2003/feature.htm