You can use any analog/i2C/UART based light sensor.
The BLE module present on the kit is CYBLE-022001 module has I2C, SPI, UARt and ADC. Please refer PSoC creator pre-populated schematic for more information on the components/blocks that can be used.
You can use the pins on Jumper j2 to connect your light sensor to this kit. Please refer page number 62 from the solar powered kit document.
You can use the ambient light sensor used in the kit CY8CKIT-044 on this Solar powered iot kit also. Please refer CY8CKIT-044 design files from the link below:
Thanks for your reply. Can the ambient light sensor be powered by the same board using energy harvesting? Or does it have to be powered from elsewhere (external power supply / battery)? If it can be powered by the same energy harvesting kit, do I have to use a low power sensor? What's the maximum power rating for the sensor to fit and be powered by the board?