Notes. Functional approximation of the measured NI-CU fluence, as function of current (I in mA) and pulse-width-modulation duty cycle (PWM in %) for all five LED channels. The fluence is the prediction per average NISP pixel and per photons per second. These ad-hoc models are of the form ƒ(v × I + w × PWM + x × I × PWM + y × I³ + ɀ × I² × PWM), where v, w, x, y, and ɀ are fit parameters across the central part of the I and PWM parameter space. The last two terms are non-zero only for LED E. The resulting relations are shown in Fig. 11.