Yeah it's faaar not enough
I put about 150 fibers on my bridges. Unfortunatly, a lots were broken during the construction process. Now only about 105 are working.
And when I take a look at my bridge, 100 fibers it's not enough. So 50... :lol
My ISD is just a bit bigger than RC's and I plan to put about 10000 fibers to get the same effect than the 8ft.
I know 50 can sound a huge amount, I thought the same, but it's nothing in fact. You've spent 3 jours to put 300 fibers, and you are very happy, thinking "wow it will be great once lit" then you turn the lights on and you think " What's the hell, looks like 10 poor fibers ! ****, 9700 more to go..."
Try to count all the tiny holes on the 8ft. Each hole is a fiber. You will be surprise to count sometimes more than 20 holes/cm².