About half the lights in my house went out after I changed the light bulb on a "tricky" fixture. I found the tripped breaker and flipped it back on. Now all of the lights will come on, EXCEPT the "tricky" one, which seems to have been the source of the initial trip. What should/can I do? Is this a serious problem?
You need to test the voltage between hot and neutral at the light fixture and also going back along the route of the circuit back to the panel. Be sure that the breaker in question also has the 120 volts hot to neutral (for breakers the neutral is over on the terminal strip where all the white wires come together).
Stop wasting time re-adjusting the pattern. Have several lawn sprinklers, one for each pattern.