Which of the following headlight issues can be hazardous?

At night your headlights will usually be the main source of light for you to see and for others to see you. You cannot see nearly as much with your headlights as you can see in the daytime. With low beams you can see ahead about 250 feet and with high beams about 350-500 feet. You must adjust your speed to keep your stopping distance within your sight distance. This means going slow enough to be able to stop within the range of your headlights. Otherwise, by the time you see a hazard, you will not have time to stop.
Night driving can be more dangerous if you have problems with your headlights. Dirty headlights may give only half the light they should. This cuts down your ability to see and makes it more difficult for others to see you. Make sure your lights are clean and working. Headlights can be out of adjustment. If they do not point in the right direction, they will not give you a good view and can blind other drivers. Have a qualified person make sure they are adjusted properly.