individual modules with RF and logic

hello everyone,

at the moment i have and arduino mega 2560 and im using it to try to control the light switchs at home, atm i have an encoder, an RF transmitter connected to the arduino, and a individual board with a decoder, RF receiver and a relay to change the state of the light switch, so far so good, now im facing a problem...
I want to know the true state of the light, cause at the moment, if i turn on the light using the board and then turn off the light using the switch, on the software i get that the light is still on but in reality it is off.
i've been told that i could use an opto-coupler so i can know if its on or not, but i need to find a way to transmit it to the arduino. the size of the board is a problem, i need it to be the smaller as possible.
I've thought about a board with a micro-controller, an opto coupler and the nRF24L01+, something like this

You think this is doable? will it be big? im planning on having this around the house, so we're talking about quite a few (around 14)

One option... use a relay in series with the light bulb and the contact connected to the microcontroller... that means you'll use two relays for the same purposee.

Another option might be something like this: Intelligent Power and Sensing Technologies | onsemi the problem is that the lightbulb will draw quite some current and you might end up dissipating lots of power on that resistor.

The other is an LDR, but that might be strange to implement in a house.

Is it that important to know that you have power in the house or that the lightbulb is not broken?

Check out the JeeNode too, small and Arduino compatible,

its not important to know that the light bulb is broken...
its important to know if the lights are on or not and be able to turn on/off remotely...

In my head what i'm asking looks easy but hardware speaking i don't know...

About jeenode, it looks basically that it could cover the part of communication, but not the most important part at the moment, that is, know the actual state of a lamp

The JeeNode has an Arduino on board, so you can use it to read the voltage and current at
the loads.

I want to control the lights too, not to measure the current...