where θ is the phase angle between V and I, and ∡θ=cos(θ)), is the power factor. It is possible that the energy delivered to the system be electrical and the lamp system has both a capacitive and inductive component, and so a phase difference between I, input current, and V a sinusoidal voltage at high frequency.
It is assumed that at steady state all energy input is converted to quanta of energy and emitted. Given a small enough scale the quantum can be measured precisely. The target material can be thorium oxide or magnesium oxide or lanthanum oxide.
