MH question

[guyfish]

I have a 400w coralvue dimmable ballast and was wondering if anyone knows if I can use a 250w bulb or will it blow?

Thanks in advance

[JD]

I have tried several experiments with MH lighting.
Running a 250 bulb on a 400 ballast will result in a whiter light than indicated. ie a 20k bulb will look like a 14k bulb.
At no time during my tests did I blow any bulbs. However, all my experiments were short term. No doubt the bulb will run much hotter and cause premature failure.

[nissannx]

i'm an electrician by trade and have replaced many mh bulbs over my career. i can almost gaurentee that any mh bulb that is under rated for the ballasat will blow under regular usuage. it wont blow right away but it will. your dimmable ballast means if you put a 400watt bulb in you can select it to act like a 250 watt bulb.

[yellowtang]

I did a test like that once....
I run a 250w bulb with a 400w coil PFO ballast.
the bulb ignited right away however after 10 minutes of use the
filament inside the bulb got very very hot breaking the filament of bulb.
also did run a 400w bulb with a 250 ballast and it just run very blue even
though this bulb was 10000k.
from my own experience I say it does not work,unless you have a dimmable
ballast which runs 175/250/400/1000.
cheers.

[guyfish]

Thanks guys

[Stussi613]

One point of clarification: metal halide lamps don't have filaments, they have electrodes.

Rather than super heating a metal filament, current is passed between two electrodes in an arc tube containing various metals which are excited by the heat produced and the electricity passing between the filaments, producing light. This is why MH bulbs have a wam up period. Also, the average MH arc tube is at roughly 18 atmospheres of pressure. When they fail, they generally produce a non-passive event - namely the bursting of the arc tube. This is why MH bulbs come with either an outer envelope, and or a fixture that has thick glass protection.

The short answer to your question is that over-driving a 250w bulb with a 400w ballast will produce more light at a higher frequency, but the trade off will be shorter life and a potentially explosive end of life event. If you can select 250w on the ballast then go for it. If you can't, don't take the risk.

[JetJumper]

From what I have read there are 2 different types of ballasts out there.  One that is dimmable and one that is multiwatt.  With a dimmable ballast you must run a 400watt bulb with a 400watt dimmable ballast and it will adjust the output of the ballast from 50%-75%-100% etc..  With a multiwatt you can power different bulbs.

[Stussi613]

From what I have read there are 2 different types of ballasts out there.  One that is dimmable and one that is multiwatt.  With a dimmable ballast you must run a 400watt bulb with a 400watt dimmable ballast and it will adjust the output of the ballast from 50%-75%-100% etc..  With a multiwatt you can power different bulbs.

Exactly.