Dear Revathi,   I recommend you to use an optical bench, where the halogen lamp and the photodiode are co-located at separation of S=1.07m.   First, read photocurrent Ip of the photodiode. Then replace the photodiode by an illuminometer under assumption of stability of the halogen lamp.  And read illuminance E and multiply it by the square of S.  It is luminous intensity Iv=S^2 L [cd] on the photodiode.  In this way, you can calibrate photocurrent Ip with regard to luminous intensity Iv.     Shigeo

For getting the expression for peak intensity for Gaussian beam after certain distance 

please visit

https://en.wikipedia.org/wiki/Gaussian_beam 

I agree, you need to measure it. The angular distribution is not uniform, so it will be pretty difficult to make a reasonable estimate without measurements