What constitutes the best way to turn an outdoor lamp on and off will depend on the type of outdoor lamp post light fixture you have and your perspective when it comes to convenience and safety. There are several factors to consider, therefore, when determining which approach is the best way for your circumstances.
What Type of Lighting Do You Need?
If you installed an outdoor lamp post fixture on your property for the purpose of merely "dressing" the front of your home's exterior at night, making it look cosy and "lived in," you will probably wish to manually turn the lamp on and off at a switch located near the front door. If this same kind of post light is located in your backyard, you should put this light on a switch near your back door entrance.
If, however, your front- or backyard post lamp needs to provide security for your property after dark, or if the lamp is supposed to light a potentially hazardous walkway, an automatic system that doesn't require your direct interaction may be a wiser and more practical choice.
Automatic Systems: Light Detection
A lamp post based on a light detection sensor will begin to turn on (in a warm-up stage) at dusk and become fully illuminated at dark. The lamp will continue to burn until dawn, at which time the lamp will begin to step down until it finally turns off completely in daylight conditions. You can purchase lamp post fixtures that operate on this technology, or purchase socket adaptors that will install in any existing fixture with a screw-in bulb base. These socket adaptors work with standard incandescent lamps but they may not work with newer CFL bulbs.
The chief drawback to a light-detector lamp post like this is the energy cost of an incandescent lamp that burns for nearly eight hours a day, 365 days of the year. A good option is to place a light-detection socket adaptor on a standard light post that also operates on a manual switch inside the house. When the indoor switch is in the "on" position the light will turn on at dusk and stay on throughout the night, but you can still opt to turn off the lamp post from the manual switch.
Automatic Systems: Motion Detection
A motion-detection type lamp post will only turn on when the sensor detects motion in the vicinity of the lamp post. You can set the range of the sensor so it turns on when something moves in front of the sensor, up to 20 feet away, or you can narrow the sensor to only turn on the light when something moves within a few feet of the sensor. You can adjust the length of time the lamp stays lit before it turns itself out.
Motion detection socket adaptors are available but these will only work in certain designs of post lamps where the lamp enclosure won't block the "view" of the motion-detector sensor located at the base of the bulb. Many motion detector socket adaptors are also bulky and may raise the light bulb so high from the socket base that the lamp post cap can't be properly sealed.
The upside of a motion detector lamp is energy savings over an always-on light. But the chief drawback to motion detectors is that, when configured poorly, they can be triggered by a passing car, a pedestrian, or pets and rodents that break the detection beam, not just invited guests coming up the walkway. Under certain conditions a motion detector light can cycle on and off many times during the night, creating a weird visual disruption: There is something disquieting about watching a post light turn on and off, on and off, on and off, repeatedly during an evening. If your lamp post can be turned off by a manual switch from inside the house, you may find you're keeping such a "winking" light turned off more than you're allowing it to stay on.