Or if you want to build one or even ask wtf I'm talking about. (They are pretty cool actually)

Not my design but I can't find the original website.

parts

120v Single pole dual throw relay "spdt"

120v dual pole single throw "normally off" relay "dpst" (dual throw if you want 240 at night)

120v duplex outlet

240 single outlet (dual if wanted)

120v cord

240 cord

120v photocell

Box to put it all in

Romex and wire nuts

How it's wired

The photocell triggers the 120v spdt relay, the relay powers the duplex plug "day" side and the other relay's trigger wire when there is light. The other pole on the spdt powers the night half of the duplex plug. The dpst relay activates the 240 plug. It's triggered by 120v but you can use any rated voltage on the poles. But that's moot as 240v is just 2 120v lines.

The reason you want the dpst to be a normally off relay is incase the photocell stops working you won't be running power 24/7 until it's fixed. You wouldn't want lights on with no fans for example.

I was thinking that it would be cheaper and easier to adapt a security light with motion detector for that purpose. If I remember correctly, there is a switch to turn off the motion sensor while leaving the photocell function intact. Then you can screw in a bulb socket to cord plug adapter.

That is dangerous as all hell with high wattage lights, a/c's and other devices.

This is designed to handle 15amps 120v and 15amps 240 all at the same time. It's overkill for 1 small light.

I agree that your set-up is more versatile. The security light is for two 150 watt incandescent bulbs and, as such, I would not use it for appliances more than 300 watts and with a power factor not near 1. But, if I needed more power, I would connect a 24 volt transformer and relay from my electronics junk drawer.

But, on second thought, instead of a security light, I would use one of these:

http://www.amazon.com/Westek-SLC5BCB-Outdoor-Indoor-Control/dp/B004YWEQQY/ref=lp_14328101_1_4?s=lamps-light&ie=UTF8&qid=1436542269&sr=1-4

Someone would likely want their grow lights on to supplement daylight only when it is cloudy during the day and during part of the night. Most typically, someone would not want their grow lights on for all of the night. In this case, the input of the photocell control needs to be connected to an actual timer with the timer set to be "On" all of the day and part of the night. As I recall, 15 amp timers with grounding plugs and sockets cost about $12 and low capacity non-grounding timers cost about $3.

The whole point is to replicate the daylight hours. You have 240v for lights and/or a/c. You have 120v on during the day for things like lights, small a/c, fans, pumps, humidifier, whatever. You have 120v at night to run whatever you may want ran at night, a heater even, if needed.

It is so versatile, any options are available. You can build a timer into it and it would be much safer than using a timer the normal way with high power and wrong type of load devices. The photocell still has its uses in that case. You can set it to turn on or off when the photocell says so but turn off after a certain time. Or come on and off multiple times as needed either day or night. It's best to be hard wired in but I can't do that where I live.

I personally use it to replicate daylight indoors. It adjusts to the seasons exactly on a per day basis. I personally would rather have less power all day then lots of power on the rare days it's cloudy. But I live in a north facing apartment so I have to fully replace daylight.

If it's not your thing I totally understand. But for people like me pretty much forced into providing the full day of light, wind, and humidity it's nice to not have to adjust timers. No worry about throwing off the seasons and confusing the plants. I am trying to get indoor citrus fruit production to be in line with when its supposed to be outside. Now the fact that I live in Michigan might be something that needs to be "corrected" for. I'm also considering switching the 240v relay to turn on at night to run an a/c only at night for my blood orange trees. That wouldn't be for another year and a half though.

A control system could be designed to operate from a computer which would automatically adjust the on and off periods according to the date and time.

What was the price of your photocell?

Free, I already had it.

Your computer idea, I already had it. It's a simple idea that is very hard to implement. My original goal was to fully replicate the weather of Rome.