The assaying of nitrogen isotope abundance using emission spectroscopy commonly requires a plasma discharge in a sample of N2 gas at low pressure (∼0.5 kPa) in a sealed glass tube. Expensive high‐power (≳20 W) radio‐frequency or microwave amplifiers are often used for this purpose. However, with correct design, a simple and inexpensive, single transistor, 100 MHz, 1 W oscillator can be used to produce a bright plasma discharge in a low‐pressure sample of nitrogen in a 6 mm diameter by 10 cm tube. The device utilizes optimal impedance matching to minimize the power requirements. The principles and limitations of the matching are outlined, and a simple feedback circuit is also described which, with the aid of a phototransistor, enables the emission intensity to be controlled. Ignition of discharge by friction or with the help of a simple piezoelectric gas lighter is also described, and construction details are given.