Sprite is black when no light

I want to make sprite invisible when there is no light, I’m using Sprite Diffuse shader and when there is no light, sprite is black. Help

Diffuse just makes it so it’s brightness is affected by light sources. If there are no light sources, there will be no light on it and it will appear black. If you want them to be invisible in darkness, then don’t use diffuse and just write that into your code. Have their sprite’s color alpha go to 0 when in dark areas.

But problem is that I want to make sprite partially visible, depending when light is, I show you here:

I know the trick with ambient light turn to black, but I want to use another light for the floor that will not affects objects.
@thetomfinch