Can you use a 250W Hps bulb in a 400W ballast?

Answer 1

NOT PROPERLY Although it may light, it will burn out pre-maturely due to the higher current flow. A ballast and its lamp must always be a proper match in any HID (high intensity discharge) application. The 400 watt rating of your ballast is NOT a maximum rating. It is 400 and only 400.

Answer 2

It is not recommended to use a 250W HPS bulb in a 400W ballast as the ballast is designed to work with a specific wattage bulb. Using a lower wattage bulb can lead to inefficient operation, poor light output, and potential safety hazards. It is best to use a bulb that matches the wattage of the ballast for optimal performance.

Answer 3

The 250w lamp will burn hotter and a little brighter than normal but will use almost as much power as a 400w lamp. The ballast is trying to push that 400w into the 250w lamp. This shortens the life as it burns out quicker from too many watts. Can possibly be quite dangerous depending on the ballast and setup.

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NO, It is against the NEC (National Electrical Code)to have un-approved combinations of Ballast and Lamp installed to an electric supply. IT COULD CAUSE A FIRE due to the ballast over driving the lamp in excess of its rated capacity.

What happens is the Ballast is in series with the lamp to limit the CURRENT through the lamp, as the tube ignites and begins to conduct electricity. As the tube begins to conduct, its RESISTANCE reduces, so that normally (If the lamp was connected straight to the mains) the actual CURRENT through the lamp would keep increasing, and eventually it would self-destruct. The BALLAST reacts with the expanding and collapsing magnetic field, and LIMITS the amount of CURRENT that will go through the BULB at a certain rating(400W), and at a fixed voltage (typically 135 Volts). Well, if you connect a 135Volt Tube in the circuit, it will initially work, but eventually will start to conduct into its maximum range of current, (for a 250W lamp this would be 1.85 Amps), but because the BALLAST is rated for 400W, will allow the current to climb up to 2.96 instead of being limited to 1.85.

This OVERDRIVING of the lamp will cause the tube's Cathodes to be burnt away faster than designed, thereby decreasing the life, and increasing the temperature of the envelope to exceed its design limits so instead of 900C, it could reach 1200 or 1500C, which would also be catastrophic to the lamp causing it to fail (explosively).

The lack of CURRENT LIMITING would also cause Circuit breakers to trip and other problems (Overheating of Connections), Burning of insulation where the lamp is affixed to the fixture, and so on. All in all not a good idea to replace a 400W HID lamp with a 250W lamp (without changing the Ballast to match).