PWM stands for pulse width modulation. The average value of voltage (and current) fed to the load is controlled by turning the supply ON and OFF rapidly. The longer the ON period compared to the OFF periods, the higher the total power supplied to the load & thus the brighter the lamp.
All Nordic Lights LED lamps that use a linear power supply can be dimmed by PWM. These are: The KL-lamp range, Spica LED N2401, Scorpius LED N4410, Antares LED N3304, & Virgo LED N3104.