I am using the TCS3210 to measure light intensity - did I choose the wrong chip? From the datasheet it looks like the output frequency is just proportional to the amount of incoming light, and that there is no set value to it (ie, lumens).
http://mouser.com/catalog/specsheets/TCS3200-E11.pdf

Am I correct that the frequency doesn't represent a certain unit of light?

 

It does within the tollerance shown on the data sheet. Not a very close tollerance, you probably should field calibrate it. What it is good at is being linear.