where \(\theta\) is the phase angle between \(V\) and \(I\), and \(\measuredangle\theta=cos(\theta)) \), 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.
