The chlorophyll fluorescence was studied in <i>Petiveria alliacea</i> plants exposed to different nitrogen concentrations and light radiation, the response was measured by two different forms; (1) measuring the photosynthetic efficiency with a pulse amplitude modulated fluorometro (PAM) emitted by a 650 nm diode and (2) measuring the fluorescence spectra caused by high power 452 nm diode with a SD2000 spectrometer. It was found out that the photosynthetic efficiency decreased in the plants exposed to high radiance and low nitrogen. Two chlorophyll fluorescence peaks were observed on 684 nm and 739 nm, the intensities in this wavelengths are inversely related with the light radiance. The correlation between the FIR and photosynthetic efficiency was very strong (r² = -0.809, p &lt;&lt;0.01); this let us conclude that the fluorescence spectral analysis induced by the diode (excitation at 452 nm) is an efficient technique to detect stress by high light intensity and nitrogen in <i>P. Alliacea</i> plants.