[siegfried-en]

You can't really measure solar energy in weight, right?

[pfdietz]

If you have an idealized mirrored box, and add some light to the inside, that will increase the inertia of the box. So in that sense the light has mass.

[freeflight]

With some creative math, and as long as you don't care about the actual practicality of the resulting metric, you can measure anything in everything.