multiple LDR sensor's / voltage divider circuits - independant of each other?

I am working on an arduino uno project with the following goal: Collect data from 4 separate LDR sensors and report the data in graph form to a web page. The data is an indication of the status of a thermostatically controlled heat zone (on/off) I have recently constructed a house that utilizes hot water plumbed through the floor for its primary heat source. The underfloor heating is very efficient, however based the subtle changes in temperature, while the system is heating it is difficult to optimize the controls. This project is designed to provide specific data related to operation. (time date each zone is on/off)
In an effort keep the data collection system separate from the formal heating system, my plan is to extract the data based on a set of control lamps that I installed in the thermostat system. The indicator lights come on when the thermostat calls for heat. I have four lamps arranged in a row and I have built a set of four LDR’s that will be placed directly adjacent to the lamps. My plan is to read the change in voltage of the individual LDR’s when the state of the light changes. (voltage divider circuit)
So all is well when testing only 1 LDR circuit. I utilized a voltage divider (10k resistor) circuit, however my question is this, when I added 3 additional voltage divider circuits and connected to 4 separate Analog inputs on the UNO, the voltage reading appear to be influenced by the others ? I direct a light source to one of the LDR’s and voltage reading changes for a 4 sensors? It feels like using a shared ground may be part of the problem? … can you provide me any clarity? … Once I get this sorted out I will begin on the webpage challenge … thanks

thermostat_project.pdf (92.9 KB)

If all LDRs are optically isolated, there should be no change in other readings.

As always, please provide a drawing of how you have wired the circuit and show your program.

The first thing newbies need to learn is how to put their code in its own window as seen in other posts. This can be done by placing     [code] and [/code]  around the code. This makes it easier for others to read.

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