The answer to 'why is my landscape lighting' is that there can be several common causes, including faulty wiring, burned-out bulbs, tripped circuit breakers, or issues with the transformer or timer. Symptoms may include some or all of the lights not turning on, flickering, or dimming.
To troubleshoot, first check the circuit breaker and reset it if tripped. Inspect the bulbs and replace any that are burned out. Check the connections at the transformer and ensure the timer is set correctly. If the issue persists, it's best to call a professional landscaping technician who can properly diagnose and repair the problem.