Hello, mesh babylonjs that looks bright in Blendar also looks dark. I increased the light setting in babylonjs but the result did not change. Can you help me?
We need a playground to be able to help.
Try to load the exported file from Blender in the Babylon sandbox. 
If everything looks as intended, then you are possibly missing an environment. 
You can quickly create an environment with
Yes, you definitely need to indicate whether you are exporting via .GLB or .BABYLON. If .BABYLON, next you need to specify whether you are exporting standard or PBR materials. Lighting is handled very differently for each.
Finally, your Blender screen shot is not a render (F12). Lighting and culling have no meaning in the 3D viewport. That is also why people report problems with normals in BJS. There being no culling in 3D viewport, you cannot detect that your normals are inside out till the file lands here.
Bottom line, it really makes little difference how it looks in Blender, especially when not rendering. People who export rarely do Blender rendering. You need lights, a camera, and the environment texture you plan to use (they do not support .ENV files).