Ian, you know that light has a energy Every time you go out in the sun you feel that energy warm you up. So no matter what equations you consider you have to admit to that.

Yor_on nailed it. There are at least two definitions of mass that make sense in special relativity, and they both agree with our concept of mass and with each other when things are moving at slow speed relative to us.

If you choose to use the one called relativistic mass, E=mc

^{2} holds, and light has a non-zero value of m so that it can have energy.

The more common choice, and the one that's used when saying light is massless, is the invariant mass. If you use the invariant mass, the proper equation is E

^{2}=m

^{2}c

^{4}+(pc)

^{2}, where m=0 for light, and p is momentum, which is non-zero.