Measurement of Work Function of Practical Fluorescent Lamp Electrodes with Emissive Oxides

Abstract

In this paper we propose a method for measuring work function of practical fluorescent lamp electrodes with emissive oxides. The work function measurement is based on the matching between the zero-field thermionic emission currents and various dc lamp currents set in a normal glow discharge by means of a lamp voltage monitoring procedure with an electrode-heating device for thermionic emission measurement. Measuring the work function of practical fluorescent lamp electrodes is a promising approach because changes that occur in the work function of aged-lamp electrodes in some lighting systems will be helpful in evaluating the system. The paper points out the doubtful approach of taking a rather small value of the Richardson constant. To solve this issue, a temperature-dependent work function is introduced. In the first stage of the paper, the Richardson constant is taken as the theoretical value. As a result, work function φ[eV] of a fluorescent lamp electrode halfway through its lamp life was measured and given as: φ=0.80+1.36×10-3T (computed from equation with T2) where T was the electrode temperature [K].Second, an attempt is made to measure a temperature-dependent work function taking a realistic value of the Richardson constant. The smaller the value of the Richardson constant, the smaller the estimated work function is. Finally, the paper examines how to take a realistic value of the Richardson constant.