One of the key benefits of motion detector lights is the energy savings these lights bring.  The light stays on less and only when needed, and less energy is used as a result.

Instead of traditional incandescent light bulbs in your motion lights, consider instead using a CFL - compact fluorescent light - or LED energy savings light in your fixture.  These lights provide energy savings over normal light bulbs.  Keep in mind that these lights provide different lighting effect, so make sure to choose the right bulb for your lighting application.

Also, when using CFLs, make sure to choose CFLs that are rated to work with dimmer switches.  This is because CFLs that are not made for dimmers will typically require the full amount of voltage in order to fire the gasses inside the fluorescent bulb.  If the power gets below the required number of volts, which may happen with certain motion detector lights (for example, using the Dual Brite system), the CFL may not receive enough volts to cause the fluorescent light to fire completely, leading to a flicker effect.  Solve this by choosing CFLs that work with dimmer lights.

Otherwise, you should have no trouble using an energy savings bulb in your motion sensor light, and enjoy the extra savings.