How to take electrical characterizations of Graphene based FET as UV sensor?

I have following details for the same!!!

For the proposed application, to my understanding from the literature review, I need to measure the drain characteristics after UV exposure for t minutes (t = 1, 2, 3, 4 & 5 minutes). But, I am having a little confusion in regard to measurement procedure. 

1.One option is that I provide Vds = Vgs = 1 V. On completion of 1 minutes, I shall disconnect the Vds supply and connect the Keithley source meter to measure drain characteristics. 

2. Another option is that I shall run the cycles of - 5 to + 5 V for Vds with Vgs = 1 V. The UV exposure shall be continuously ON for the whole time of measurement . At the end of t minutes + cycle time  ( Here, lets say t = 1 minutes) , I shall turn off the Vgs and Vds. On extracting the data (excel file) from source meter, I shall search t =  1 minute and plot one cycle of drain characteristics for that point.