A description of the radiation emitted by impurities from within a plasma is crucial if spectral line intensities are to be used in detailed studies, such as the analysis of impurity transport. The simplest and most direct check that can be made on measurements of line intensities is to analyse their ratios with other lines from the same ion. This avoids uncertainties in the plasma volume emitting the radiation and the absolute sensitivity calibration of the spectrometer and, in some cases, the need even for accurate measurements of parameters such as electron density. Consistency is required between the measured line intensity ratios and the theoretical values. For some elements, this can lead to the determination of parameters such as the electron temperature of the emitting plasma region. Carbon was the main low Z intrinsic impurity in JET and an analysis of spectral line intensity ratios has been made for the C IV radiation emitted from the JET divertor. Agreement is found between the measured and theoretical ratios to within the experimental accuracy of ~ ±10%. This has allowed the electron temperature of the emitting region to be determined and estimates to be made of the contribution of charge exchange recombination to the electron energy level populations. The analysis has been made for a database of Ohmic and additionally heated phases of a large number of pulses and the importance of dielectronic and radiative recombination as well as ionization has been investigated. In addition, the development of Te throughout two example discharges is illustrated. The agreement found between the measured and theoretical C line intensity ratios for the C IV divertor emission contrasts with that from the JET scrape-off-layer, for which there are discrepancies.