How to say "it is actually something that does something"?
The usage of 是 is correct.


  是 ( shì ㄕˋ )
  〈动〉
  (5) 表示肯定判断之词 [be]


I think it is actually the idea that can really light up the future.
其实我觉得是主意点亮未来。
我觉得其实是主意点亮未来。
我觉得其实是主意才能真正点亮未来。

To emphasize it, you can add 应该. (contrast to 梦想)
其实我觉得应该是主意点亮未来。
我觉得其实应该是主意点亮未来。
我觉得其实应该是主意才能真正点亮未来。

You can also use 想法 or 点子 for 主意.