How to programmatically turn off the screen of an Android phone?

Question

How to turn off the screen of an Android phone programmatically? I tried using the following code with no luck

PowerManager mPowerManager = (PowerManager) getSystemService(POWER_SERVICE);
mWakeLock = mPowerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "MYTAG");

mWakeLock.acquire();