You need to replace the bulbs in the lights.
Check the fuses and bulbs. The year, make and model vehicle info would help.
You could have a fault stalk switch, a wiring fault, or a defective high beam relay. If the high beam circuit is fused separately, it could also be a fuse.
Low beam bulb is burnt out. Replace it.
It's a Cadillac, what do you expect?
Its possible that the low beam filimant is burnt out or if you have separate lamps for high and low, that could be it too. You can lookup your vehicle below to see if you have separate high and low beam lamps - this may help - see sources and related links.
the bulbs in your car have two filaments, high beam and low beam. as you generally use mainly low beam the filament wears out a lot quicker than high beam. so replace your bulbs, as it couldn't be anything else.
You need to change the light bulb, the high and low beam on some vehicles are contained in a single bulb. or you could have a bad connection on just that one light
most likely problem is that the low beam side of bulb or sealed beam is burned out replace with a new one
Try changing the bulb that doesn't have the low beam. Check at your local auto parts store for the correct bulb.
Replace your dimmer switch and this should fix your problem Or both bulbs could be bad
Most likely the vehicle has separate low-beam and high-beam headlight bulbs and you simply have one low-beam bulb that is burnt out.
low beam, 9005 will be the high on that vehicle
All vehicles are required to have low- and high-beam headlamps. If your low-beam headlamps both fail after dark, try switching to high beam. If the high beams don't work either, switch on the emergency flashers. In either case, get the car out of traffic and off the road as quickly as safely possible.
It is very likely the bulb. The low beam gets much more use and most often fails first.