This thing is really cool. I wanted something that I could use to put my porch light on a timer with a CFL bulb, and this works perfectly.
Some of the other products available (including light sensors and other timers, as well as a Honeywell timer similar to this one) only work with incandescent bulbs, which totally defeats the purpose of putting your lights on a timer to save energy. I could run my 26-watt CFL (100w equivalent) all day long and still use less electricity than using an 8-hour timer with a 100-watt incandescent.
This model allows you to program either a single on/off cycle to repeat every day, or up to 7 separate on/off cycles for each day of the week. I believe you can also set an every-day on/off cycle and combine it with 6 additional day-specific cycles if you want to. The cover to the programming buttons functions as the manual on/off switch, and using it does not interfere with your programs.
I had some trouble figuring out that you have to slide a toggle under the button cover to "ON" before the switch itself will work AT ALL. I thought that was a bit confusing in the instructions, so now you'll know. Programming is not difficult but it took me a few tries to figure it out. When you are finished programming, you just close the cover and press it once as if you're turning the light on, which will exit programming mode.
There is another model available that also works with CFLs and can be set to vary the on/off times with your local daylight calendar (
Honeywell Econoswitch RPLS740B 7-Day Solar Time Table Programmable Switch) but for the extra cost, I didn't need that feature.
To use this product, you need to have a light switch where the power enters at the switch rather than at the light fixture. That's because the timer itself needs to have electricity to it in order to work while the light is turned off. If the power enters at the light, shutting off the light would kill the power to the timer. Most houses are wired the correct way, and typically this means at least 1 pair of black/white wires entering the switch box. If there is no white wire, only two black wires or a black and a red, you won't be able to use this timer.
As a side note, this switch has some sort of capacitor inside that saves your programs during power outages. It isn't a battery, so you would never need to replace it. I have not had any extended outages so I don't know how long it will remember your programs, but it has worked fine through a couple of brief outages so far.