Low Power LED detection : Voltage Divider or RC Time?

[Puneit Thukral]

Hello
I have a smart meter in my apartment on which an LED glows when the power supply switches from the grid to a backup ( in case of load shedding etc).
Today, I use an Nodemcu running ESPhome to detect the LED glowing on or off status by doing a voltage divider on a LDR. This is being powered through a phone charger. I check the status on a digital pin.

Now, in order to improve the WAF points, I need to make is battery operated (wires are ugly - simple), hence I would like to run it on Arduino Pro mini running MySensors & AA/AAA batteries
Which is more power efficient - LDR with voltage divider or LDR with a capacitor using the rctime library?
Year to date LED was on 103 hours

[skywatch]

@Puneit-Thukral A photo-transistor maybe better as it will draw less current in 'off' mode. Google phototransistor applications and there will be another learning opportunity for you ;)

[idanronen]

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