Connect the switch "downstream" of the photocell - that is, between the photocell's hot output and the hot wire to the light.

Placing the switch anywhere in the circuit will shut off the light. But photocells typically are "ON" unless electrically energized AND exposed to suitable light levels. If power is interrupted at the house, when the power is restored, the photocell will be ON for about 45 seconds, even in daylight conditions. The third wire to the photocell is to keep it energized even if the power it controls is interrupted. To wire it this way, a 3-wire cable would be needed from the house to the lamp post. The red would power the photocell and the black would power the light.

David & Bus Driver, thanks. I couldn't put a three wire cable from the lamp post to the house because the photocell will be on the house about 20 feet away from the post. Would it work if I connect the red wire from the photo cell to the black wire from the source. One wire from the switch to the black wire from the light and the other wire from the switch to the remaining black wire on photocell? I thought that when I do wire it it would work this way but I wasn't sure. I want to make sure before I begin the project. Thanks again for your help

I forgot to mention that another reason I want to put a switch in the house is so I can use a dimmer switch on the light. It will be a three head light that can use 3 100watt bulbs. I will probably use the 100 watt bulbs but will dim the light.

I don't remember which wire from the photocell goes to line and which to load. It may vary with different brands. The diagram or instructions with the photocell will tell you.

The line wire from the photocell (will be red or black) goes to the black from the source cable, and the white to white from source (the white wire to the light also joins these whit wires). The remaining wire from the photocell (load) goes to the white wire in the cable leading to the switch. Put a piece of black tape on both ends of this white wire. Then the black wire in the cable to the switch goes to the black wire leading to the light.

If you want a dimmer, use it in place of the switch. IMPORTANT: Make sure the photocell is rated to switch fluorescent loads! Any other type of photocell may not work properly with a dimmer.

Three hundred Watts is a LOT for an outdoor light on a photocell. At a rate of 10 cents per kWh, that will cost you about $130 a year to operate. Dimming will reduce this but not as much as you might think.

I suggest that you use compact fluorescent lamps of the brightness you want. This will cut the cost of operation by at least 75%.

Do not supply the photocell from a dimmer. Place the dimmer (electrically) between the photocell and the light. The photocell is not just a simple switch. The photocell requires regular 120 volt electrical power for it's own operation.

Bus Driver, are you talking about bringing a 2 wire cable from the light into the house to the switch first, then a 3 wire cable from the switch to the photocell and a 2 wire cable,of course, from photocell back to breaker box? If the red wire from the photocell is connected to the black wire from the source, would that not give the photocell a 120 volts all the time regardless of where the dimmer was placed?

I'd suggest a motion sensor instead, most of them incorporate a photocell, your energy consumption will be a lot less, and it'll just be on when you need it, if you need to leave it on, say when you're outside, most allow you to lock them on, by a rapid flick off/on of the switch.

I think the idea of the dimmer's unwise and probably prohibited by most sensors of these types, I suspect you'd fry them.

jimmy, this project needs an experienced electrician. Call/hire one.

You could bring power first to the box for the photocell (14/2). Go to the dimmer with (14/2) as a switch loop. Go out of the box to the post light with (14/2). If it is on a 20 amp circuit, the wire needs to be 12/2. The incomming hot connects to the black of the photocell. The red of the photocell connects to the white of the switch loop. The black of the switch loop connects to the black going out to the post light. The incomming neutral, photocell neutral, and neutral to the post light connect together. The photocell would have to be able to work in series with the dimmer. Turing off the dimmer switch would kill power to the light without turning off the breaker.

Thanks Spencer and everyone here. That sounds logical to me and similar to what I thought. When the light is off during daylight hours, if the dimmer is turned down very low to dim the light when the photocell turns on the light at dark that wouldn't keep the light from coming on. You should have the light that the dimmer was set to before the photocell previously turned it off. To make it brighter once it came back on, all one would need to do is turn the dimmer knob up. The photocell would still be getting its 120 volts with the dimmer set at low dim because it would be wired to the main source. The light would come on as to where the dimmer was set for the light, either bright or dim setting. The photocell I have seen at Lowes states that it is compatiable for 120 volts and 15 amps and the dimmer switch states it is compatiable with 15 amps, single pole, and 600 watts. Thanks again!

Jimmy, you'll be OK as long as you get a photocell that states it can be used with fluorescent loads. DO NOT use one that says "incandescent only." It won't work right with the dimmer.

Thanks, David. I will keep that in mind and make sure I get a photocell like that.

It worked! I can use both my photocell and dimmer switch. Can set the dimmer to real low and light will still turn on by photo and turn off by photocell with no problem. Thanks to everyone for their help and especially Davidr and Spencer.

I had the same problem, then realized that the photocell needs a minimum voltage to operate, and the dimmer messes this up.

Does anyone know where I can find a photocell like Jimmy used? The big orange box had one that said no dimmers.

Look for a photocell which specifies that it can be used with fluorescent lights. Most post light photos are of this type.