Look very carefully

Where is the light source?
Yes, it's catching the top of the bellies of the railings at the left hand end of this balustrade.
And yes again, that means that each of these railings has been hand-painted in four different shades of blue, carefully blended from each shade to the next to suggest that the light comes from below.
They used to be black. So either Anahata is making a fortune and can afford a specialist paint job for their railings which most people won't ever notice, or they have too much time on their hands and find that concentrating hard on something complex and creative is a more hands-on form of meditation.