Multiple photresistors

Good afternoon, I am working on a project and I am trying to connect to photoresistors to the Arduino to read a time difference between when each resistor's voltage changes so I can calculate the velocity of a projectile. Any advice would be very helpful on how to do this. Thank you.

int lightPin = 0; //define a pin for Photo resistor
int threshold = 500;

void setup(){
Serial.begin(9600); //Begin serial communcation
pinMode(13, OUTPUT);


void loop(){

if(analogRead(lightPin) > threshold ){
digitalWrite(13, HIGH);
digitalWrite(13, LOW);


If the projectile is going more than a few meters per second, a photoresistor is not going to work. Thy have reaction time that is too slow. For example circuits do a search for diy photogates

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