LTR4206E replacement

Yes you can take any phototransistor instead of a LTR4206E.
The only constraint, is to have a voltage (measured with a classic multimeter in voltmeter mode between gnd and tpA), when exposed to common light conditions, around 1 ou 2V very approximatly (the exact absolute value is not very important).

2 cases :

1. the voltage is very low : Check that it is increasing when exposed to stronger light source. If necessary, you can replace the serial resistor (1k or 10k on my schematic) by a bigger one. The voltage will increase, and the current consumption will decrease (nice !).
2. the voltage is too high (near vcc or worst : Clamped to the maximum) : It's bad, when a flash will appears, the voltage won't increases very much because it's almost at the maximum, so the resulting pulse amplitude will be very small and probably too much. In that case you will need a less sensitive phototransistor or you can try to reduce the resistor value, but be carefull, is the resistor is too small the current consumption could be very high.

max phototransistor current = Vcc / R

1kohm generate 1mA current, but 100 ohms => 10 mA (the battery life will decrease !)

I'm not sure that my module would works with photodiode. I don't know very well this component, but i suppose that it reacts in a go-nogo way. Something more "progressive" is needed.

Please, contact me to tell me if your module works when finished, and what type of component you choosed and how it reacts.