This paper presents modeling of transient thermography in terms of equivalent electrical parameters, its simulation using a popular circuit simulator SPICE (Simulation Program with Integrated Circuit Emphasis), followed by experimental verification. A novel current source based electro-thermal modeling of radiative heat sources is introduced. Analytic comparison of thermal and electrical circuits forms the basis for modeling and simulation of transient thermography experiments, in which the current source (modeling rate of incident radiative energy) drives a 3- dimensional (3-D) Resistance-Capacitance (RC) network (modeling heat conduction in the material). The current source value was derived from pyranometer-based measurements of the heat flux from the source. A mild-steel sample with a blind hole below the front surface, irradiated by a heat pulse, has been modeled by the proposed technique. SPICE then simulates the absolute thermal contrast of the surface as a function of time, in moderate computing time (seconds). The simulations compare well with experimental observations and similar to generally reported results. Current source approach, allows estimation of radiative heat flux necessary, to view sub-surface defects in a given material, at different depths, in general, and to predict time and magnitude of surface temperature over the defect and non-defect region in particular.