Abstract: By analyzing the working mechanism of the low-pressure sodium lamp，it is found that the plasma in

the low pressure sodium lamp is in non-local thermal equilibrium state. Therefore，this paper uses the corona model

suitable for non-isothermal plasma to calculate the intensity ratio of sodium doublet in the sodium atom spectroscopy

experiment. The calculated results agree well with the experimental results，with a five percent error，which gives a

good explanation for the experimental phenomenon.

Key words: low-pressure sodium lamp, line intensity, non-isothermal plasma, coronal mode