You are looking at a Light Bulb with a built in Dusk to Dawn Sensor.

This is a neat unit to use to get some light when it gets dark without always flipping a switch
It will screw into a regular E27 light bulb socket.

This is a nice option for my lighthouses. You just plug your lighthouse, "or any other outside light for that matter" into a 110 volt receptacle and install this unit and you won't have to search for the door knob in the dark. Automatic on and off switch.

Tip: Set your lighthouse far enough away from the front door to keep the mosquitoes  and other bugs away from the front door.

Dusk to Dawn Sensor Features

• Turns Lamp on at Dusk
• Turns Lamp off at Dawn
• Fits into any standard E27 Lamp Socket

Instructions

• A. Screw the bulb into light fixture. The sensor opening should be positioned to receive maximum daylight.
• Caution: Screw in only until the bulb is secure and the sensor is correctly oriented. Do not over tighten.
• B. Turn on the power (and leave it on for automatic operations.)

Operations

The dusk to dawn bulb uses an electronic switching circuit and a special photocell which senses light through the window, depending on the position of the sensor. The ideal sensor position lets in enough light to turn the light on, yet reduces unwanted blinking.

It is a nice add on for lighthouses or any other light you would like to have come on automatically.