This is the most common sign. The light is much,much brighter than it usually is, that means it is within minutes of burning out.;
,, The light is dimmer than usual, or doesn't turn on. It could be that it blown out already, you are too late.
 The light takes a long time to start up. This means either a bad electricity current, or that it is going to burn out immediately.
 The light flickers, this may mean it is badly connected/screwed in, or that the connection is connecting, and splitting, probably already burned out.
 A fluctuating brightness definitely means it is about to blow up. Disconnect or switch off immediately.
Watch for an increase in light brightness.
Listen: A strange squealing will come from the bulb, or a buzz, this signifies vibration that can cause the connection to break and fail.

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Notice dimming.
Observe how long it takes for the light to start up.
Watch for flickering.
Notice for light fluctuations.
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