Subject: how do I measure phototropism ?

I dont understand how to measure phototropism. Do i do it i terms of degrees of 
groth towards light from the original position? If so how? If there is any 
other way kindly assist.
I am doing a lab on how phototropism is affected by different coloured light. I 
have a methodology etc, aplan and everything I just dont undertand how to do 
measure phototropism. This lab shall be used to help me in my IB extended essay.
Thank You

Re: how do I measure phototropism ?