Hi. I have two light at my front door one on either side. I have installed motion sensor fixtures to both. The light switch is left in the on position. The voltage seems correct. Sensors work correctly. The problem is, the bulbs keep blowing in one or the other fixture. It alternates which blows. Getting very expensive and aggrivating. Any ideas?

What kind of bulbs?

Both regular and led

Regular incandescent bulbs will blow from excessive heat, vibration or over voltage. Don't know much about LED except that they are light emitting diodes, are very efficient and generate very little heat. I believe that they can be sensitive to excess voltage.
You have to be careful of the wattage of the bulbs in exterior fixtures because the fixtures can be totally enclosed and restrict heat dissipation. A regular incandescent bulb is sensitive to vibration once the filament gets hot. A LED bulb should not generate very much heat and I have never heard anything about them being sensitive to vibration. If you are being subjected to frequent voltage spikes that should also affect other lights in your home.

I would try a CFL bulb. If you regularly blow those I would conclude that there is something defective about the fixtures, although I cannot suggest what.