#include<stdio.h>

double F_get_photons(double t, double LAMBDA, double RADIANCE, double PIX_A);


double F_get_photons(double t, double LAMBDA, double RADIANCE, double PIX_A)
{
  double j;
  double pi=3.141592;			// PI the famous number			       
  double h=6.63e-34;			// Planck constant Js
  double c=3.00e8;			// c speed of light m/s
  double f=8;				// f, f-number of the illumination system	
  double phot;
  double a;				//area of the pixel

  printf("Lambda: %.10f ->",LAMBDA);
  LAMBDA = LAMBDA*1e-9;			// from nm to m			
  printf("%.10f \n",LAMBDA);

  printf("Texp: %.10f ->",t);
  t=t*1e-9;				//from ns to s
  printf("%.10f \n",t);

  printf("Area: %.10f ->",PIX_A);
  a=PIX_A*1e-12;			// from um^2 to m^2
  printf("%.15f \n",a);

  j=pi*RADIANCE/(1+(2*f)*(2*f));	//irradiance
  printf("Radiance %.15f \n",j);

  phot=j*a*t*LAMBDA/(h*c);			//number of photons
  // phot =5;
  printf("photon %f \n",phot);

  return phot;

}

main(){
  printf("%f\n", F_get_photons(100.0, 1.0, 1.0, 1.0) ) ; 

}