The responsivity of silicon trap detectors commonly used as calibration standards today is to 99.5 % defined by the values of fundamental constants when accounting for calculable reflectance losses. With predictable quantum efficient detectors (PQEDs) the percentage contribution from fundamental constants to the responsivity increases to 99.99%. The simple structure of the PQEDs make s them well suited for three dimensional modelling and opens a new path of traceability where the spectral response over a wide spectral range can be extracted from a model fit of current voltage (I-V) characterisations done at one wavelength only.