globe is too drak

1. A concise explanation of the problem you're experiencing.

viewer.sceme.globe.enableLighting = true,globe is too drak

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you're using, your operating system and browser.

You should be able to tweak the lighting parameters as shown in this example:

Does that help?

thanks , it's so helpful