= Optical-electrical heating non-equivalence
<Optical-electrical heating non-equivalence> means that equal absorbed optical and electrical <powers> do not necessarily give identical <thermometer> responses. <Light> and the heater may deposit <heat> in different places, producing different <temperature gradients> and different routes of <thermal conduction> to the support. Holding one <thermometer> reading fixed need not hold every part of the cavity at the same <temperature>. This differs from incomplete <radiometric absorptance>: one concerns where absorbed <heat> goes, the other how much incident <light> becomes absorbed <heat>.
A useful accounting convention is
$$
P_{\rm in}=\frac{\Delta P_h+\Delta Q_{\rm out}-\Delta P_{\rm par}+\delta_{\rm ne}}{a},
$$
where the signed correction $\delta_{\rm ne}$ is determined by characterization of the instrument and represents the residual departure from the lumped <electrical substitution heat balance>. It is not a universal extra source of <energy>. Varying the beam location or heater location, comparing equivalent temperature excursions, and checking repeatable dark returns can test the assumptions; no single small correction proves that every other correction vanishes.
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