I need to determine the total luminous flux of an LED lamp. I have readings of the intensity (I) at a range of given latitude and longitude angles ($\displaystyle \theta, \phi$), but I do not know how to solve with the equation given for calculating total luminous flux:

$\displaystyle \int^{\pi2}_{\phi=0} \int^{\pi}_{\theta=0} I(\theta,\phi) \sin\theta d\theta d\phi$

My knowledge of calculus is quite limited as I have only this year started to learn it at school. I would really appreciate an explanation of how to apply this equation!

Thanks in advance.