Do I need to keep a light on the live rock in my sump?

I have a bunch of live rock in the refugium section of my sump. 
Do I need to keep a light on this rock? Or can it be in relative darkness? There will be some indirect shadowed light hitting it from my frag tank but that is it.

 

word on the streets is that if you have a light on your sump when the display lights are off it helps the ph stay more stable.

 

+1
And to the comment about it keeping pH more constant, that's only true for macro algae, not rock.  The pH rise (or sustaining) is caused by the macro algaes photosynthesis.  The bacteria on the rock doesn't use photosynthesis and therefore would not be able to maintain the pH.
--AJ

 

Thanks I am going to turn that light off then.