Arduino Brightness Control

when I started learning Arduino for some projects.. i think Whats the use of doing this besides knowing commands to do?
Then I got a Reply for such stupid question..
I have a Whiteness Meter, Which is used to Measure the Whiteness of some Chemical powder...
But the output Value is changing With the Outside Sun lightning..
so i Did this
 

I made a Box and put the meter in it and placed the Leds Which are controlled Serially..