  In this paper, we define energy-momentum density as a product of the complex
vector electromagnetic field and its complex conjugate. We derive an equation
for the spacetime derivative of the energy-momentum density. We show that the
scalar and vector parts of this equation are the differential conservation laws
for energy and momentum, and the imaginary vector part is a relation for the
curl of the Poynting vector. We can show that the spacetime derivative of this
energy-momentum equation is a wave equation. Our formalism is
Dirac-Pauli-Hestenes algebra in the framework of Clifford (Geometric) algebra
Cl_{4,0}.
