I have a CFL in a desk lamp that I keep on for several hours every day. Recently, the CFL has been randomly turning off. There is no flickering before the CFL turns off like I am used to with incandescent bulbs when they are going bad. If I tap the lamp with my finger the bulb instantly turns on again.
Is this an indication that the bulb is going bad or that the lamp has a bad connection?
It's impossible to say for sure without inspecting the lamp, but it sounds like a bad CFL. Have you already checked to be sure that the bulb is screwed in securely?
You could use a multimeter to check for continuity through all of the wires to the socket (which can be difficult when trying to find an intermittent connection since digital multimeters displays don't update instantly, a meter with an audible continuity tone would be useful).
However, If this is a standard lamp with a screw-in CFL bulb, there's a simple test you can do that only costs a couple dollars (or may even be free if you have a spare CFL bulb in the house or can "borrow" one from a different lamp):
Put a new bulb in the lamp and see if it works.
