I am able to get pretty high on scales, but when I start singing, because I sing opeara I tend to get very heavy. I can sing up to the high c wuth scales but can hardley get get up to f sharp. Any exercises to lighten up the voice a bit?
Thanks

Do you mean to reach higher notes or lighten up the timbre of your voice?

I think he means he's keeping the sound heavy and that is preventing him from going higher.

Assuming opera singer is a he. xD

Are you able to vocalize up to an F# in your light voice? Because if you aren't, you can't expect to have control over that area in full voice.

As Jaime says, picture your voice as a triangle. The voice should get more condensed, more piercing towards the top. This also means decreasing breath pressure. Do extremely quiet, non-breathy scales, and consciously decrease your breath pressure (even if you get quieter) as you go higher. The less breath you use, the more control you gain and the easier it is to negotiate between registers.

I have really been noticing this in my voice recently. When I would vocalize lightly, I would hit a wall at about E5. I started to strain (even though it was quiet!) and couldn't go any higher. Then I remembered Jaime's advice about the voice being shaped like a triangle, getting smaller at the top. So I consciously made the sound smaller as I ascended. It took a few tries, but with the right breath pressure, I just zipped right up into the next register and could vocalize notes as high as C6! Of course, I am not a master at this yet and still must work out this "secondary break". But decreasing the breath pressure definitely helped me a lot.

Although I haven't progressed that far, I imagine that once you have control over this higher register, you can add volume and use it in full voice. This is obviously how Jaime has gained full voice notes up to C#6!

My falsetto only goes up to F5.

Don't worry about it Andrew. When I first started using it my falsetto only went up to the C5, but it's expanded into the occasional whistle register note... and I don't really work on it very much, just the occasional falsetto slide. So I'm sure if you really work on it, your falsetto will expand.

Yeahhh, I can only get up to F5 in falsetto, but I can do what I think is whistle without much trouble. I can't slide it down into falsetto, maybe because my falsetto has never gone that high.

But will the voice get stronger on the top?
Or will it always stay light?

Follow the program as suggested in the book and you can lighten and add power at your choice;) Try to do some light singing like explained in the warmups section and some reverse TT exercises.