The effects of light and temperature on the net primary productivity (NPP) of fodder galega (G. orientalis Lam.) were studied in two series of experiments. NPP was determined under laboratory conditions using a stepwise change in photosynthetic photon flux density (PPFD) from 0.0 μmol m−2 s−1 to 1.21 × 103 μmol m−2 s−1 at temperatures of 5, 15, 18, 25 and 31°C. NPP was 0.0 mg CO2 gDM−1 h−1 at a PPFD of 1.1 × 102 μmol m−2 s−1 and temperature of 5°C. A PPFD of 1.21 × 103 μmol m−2 s−1 produced 4.44 mg CO2 gDM−1 h−1 at 5°C and 7.15 mg CO2 gDM−1 h−1 at 15°C, but 5.57 mg CO2 gDM−1h−1 at 25°C. Average night respiration was 2.24 mg CO2 gDM−1h−1. The highest average NPP under experimental conditions was 8.56 mg CO2 gDM−1 h−1 with a PPFD of 1.1 × 103 μmol m−2 s−1 at 31°C. An equation was developed for fodder galega to illustrate the relationship between photosynthetic photon flux density and temperature as independent variables and NPP as the dependent variable. The optimum temperatures for NPP of fodder galega were from 12.5 to 32°C in minimum light conditions of 7.26 × 102 μmol m−2 s−1 and a maximum night‐time temperature of 15°C. The potential maximum NPP was about 9 mg CO2 gDM−1 h−1 and occurred at a temperature of 23°C and a PPFD of 1.21 × 103 μmol m−2 s−1 Fodder galega required increased illumination at the beginning of the vegetation period.