This paper presents the variation in current harmonics injected by the LED lamps and their effect on harmonic estimation in the low-voltage network. Lighting consumes a significant portion of total electricity consumption in residential, commercial and industrial sectors. The energy-efficient lights, for example, light-emitting diode lamps, are reducing this share significantly over the last few years. These nonlinear LED lamps are the source of current harmonics and reduce the power quality in the low-voltage grid. The estimation of the magnitude by which they affect the power quality is essential for network operators. However, the thermal stability of the lamps is a prime consideration for the accurate assessment of the power quality. This paper investigates the effect of thermal stability on current harmonics injected by LED lamps.