is it possible that there is no light but there is casting shadow? Or is it because the light is very similar to the background color?
Because they play with colors. You can have it by applying the same color as background. It is the light where you initially enable casting shadows.
sorry for keep asking question. it will be last one xD is it possible to connect light and character so that there is constant casting shadow? when i connected, shadow doesn't work? i just have to use multiple lights?
Well, we do have the option but the shadows doesn't work in that case. It'll be just a glowing effect if you attach a light to character with Cast Shadows unchecked. If we check the Cast shadow option while the light is attached to character it won't work. We also have the option to add a light to character in Animation editor but still only can be used as glowing effect. Or I might be missing a trick here. Above is what I am aware of. May be there is a way but I'm not aware of. So to me you'll have to place the lights where you need them.