Does anyone know what would happen? Does the ballast limit the power? If the T5 HO lamps were less expensive than T5 non-HO lamps, would it be ok to just use them in a non-HO luminaire?

2 Answers 2


HO bulbs prefer more power than regular bulbs. They will work on a normal ballast, but won't give peak performance. A normal bulb in an HO ballast will be overdriven to its destruction.

What, you say? How can this be? You are accustomed to constant-voltage devices - plug a nightlight into a 20A circuit, no problem. Fluorescent tubes are current devices - like LED chips but even moreso. They are non-linear and do not act like a resistor. They act more like a dead short and will draw unlimited current. They need external ballasts to limit their current to spec. The ballast will push through spec current whether the tube can handle it or not!

  • That makes sense. Do you know how HO bulbs are able to handle the extra power? Bigger filaments than normal bulbs? Nov 3, 2017 at 18:18
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    Gas discharge tubes have no filaments and are just tubes of exotic gases and other chemicals, which like to make light when excited by an arc. In fluorescents, the gases make UV light and the phosphor coating transforms it to visible light. I assume they use more exotic/expensive gases and phosphors whose cost would not be warranted in a normal tube. Nov 3, 2017 at 18:23

The HO bulbs require more power output to operate than regular bulbs... and that is why there is an HO ballast, to provide that extra power. You could put a regular bulb in an HO fixture, but not vice versa.

  • HO always needs more power... Standards pull only what they need. As will all power supply type devices, the source can feed less load, but not more. Aug 9, 2013 at 21:07
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    @FiascoLabs This information is simply not correct and is dangerous advice. Do not do this! Florescent devices are negative resistance devices and do NOT work the way you think. See: diy.stackexchange.com/questions/58111/…
    – Ariel
    Jan 20, 2015 at 20:31

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