I'm pretty sure it's 12v as most riding mowers are. Sometimes it says it on the battery, or you can measure the battery with a voltmeter/multimeter.
Also make sure that the light bar can tolerate a bit more than 12v. When the mower is running, the voltage can go above 14v. I replaced the headlamps with LED bulbs on my mower two summers ago and most LEDs are now burned out and the individual LEDs have fallen off.
Automotive LEDs should be good for the slight over voltage as a car battery charges at 13-14v and that's what the car system runs at when the engine is running.
Another thing to think of if you are running off the light circuit is that in many systems the light circuit is AC. That is true for those systems where the lights are only on when the engine is running. That can be a problem as cars only get AC.

I think you meant to say cars only get DC...
SBL has this little beauty that throws 2510 lumens for $79.95.
4" Quad Row Heavy Duty Off Road LED Light with Multi Beam Technology - 36W | Off Road Light Bars | LED Work Light & Off Road LED Light Bars | Super Bright LEDs | Super Bright LEDs
Granted the light bars are much cheaper but, running at even 1/2 speed, they may not reach far enough to cut at a comfortable pace.


