Variable Wattage Lamps

[solaeros]

Ok I'm told you can't run a lower rated lamp from what the luminaire itself is rated for ie: 250 watt MH Lamp in a 400 Watt MH Luminaire. I don't understand this, to me it's like saying you'll burn up a 100 amp service if run off a 100kva transformer. Shouldn't the lamp create the load and not the ballast? Would it be a capacitor issue? Could it be a wives tale?

 

[mdshunk]

The capacitor and the starting device are sized for the particular wattage of the lamp. That would be like taking the cap and potential relay for a 3 horse motor and trying to use it for a 1 horse motor. Ain't gonna work, or at least won't work for long.

 

[iwire]

Along with Marc's comments I will add that is also important that the ballast match the lamp.

A ballast does not supply a constant voltage to the lamp, the ballast maintains a certain current in the circuit. The lamps are designed to run at certain current.

If you where to wire a typical HID lamp directly to the line the current it draws would keep escalating as it warmed until it tripped the circuit.

 

[480sparky]

A great source for info on HID lighting & ballasts is Advance Transformers' Literature Page. Tons of downloadable .pdfs.