Humidity and Temperature
There are many generic humidity and temperature sensors that are cheaply available. Some connect to a smartphone via Bluetooth and provide a graph of data while others incorporate a smaller LCD to display current readings
Light Sensors
"Quantum" sensors are able to measure the intensity of a light source accurately but are very expensive. Alternatively, there is an ios only app called Korona - Plant Light Meter that can measure PPFD[1]
Digital pH Meters
References
- ↑ Korona whitepaper https://growlightmeter.com/whitepaper/