I replaced one EJ500 switch – that I had with an incadescent spot light so that I could use an LED light buld instead. The EJ 500 switch is not compatible with LED or mercury (CFL) bulbs. I also replaced a standard toggle switch that I have been using mercury (CFL) bulbs that had built-in photosensors. They are no longer available since photosensors for mercury (CFL) bulbs are now available. However, the photosensor that I purchased to work with the CFL bulb added 1-2 inches of height and did not fit correctly into our fixture.I have had the EJ500 for about five years – and since I installed it and programmed it, I have not touched it since. We have frequent power outs and surges due to storms/lightning and in all of that time the program has worked without any input from me.This time, when I installed the EJ600, I told it sunup and sunset were 30 minute earlier and later, respectively. When I gave it the exact sunup/sunset times (in the EJ500 that I have been using), the bulbs came on a little later in the evenings than my wife liked and went off a little earlier than my wife liked.Installation of the switch is fairly straightfoward except that they must be connected in the so the electricity flows through the switch in a particular direction. Since both of my wires that were to be connected to the switch are black (instead of black and white), I had to put them together and then switch them if (when!) they were wrong. They were both backwards and I had switched them both after I connected the switch and found that the light bulbs did not respond to pushing the front panel which is essentiall on/off if you want to control the lights at other than the programmed times.I had some trouble (with both the EJ500 and EJ600) in programming the lights. There are six separate buttons with dual functions for most to control the programming. I use the switch in the SUNUP/SUNSET mode. When programming the switch, I needed my readers and a magnifying glass and a good light (and a third hand) to be able to see what I was doing. That may be just my age; but even when I could see what I was doing, I found it hard to follow their directions for programming the light. I ended up reprogramming it each afternoon until the program finally worked.Overall, I would recommend the switches. I would get the EJ600 because it can handle LED and mercury (CFL) lights. Once they are installed (fairly easy) and programmed (a challenge for me), they will work for years without any thought to them. It was worth a week of aggravation to program them. I had to purchase a new face plate for the large switch size.