dimming an Ikea Jansö with Arduino
I've found 2 watt warm white LED with inbuilt current control at a supplier that appears idential and they give the following description:


  What makes these interesting is that they have two AMC7135 250mA ICs in parallel to provide 500mA of current to the LED. Note that the regular AMC7135 provides 350mA, these appear to be a 250mA version and we have tested them and they do indeed feed the LED with a fixed 500mA in total. There's also a small chip capacitor onboard for proper operation of the ICs. 


Looking at the AMC7135 Datasheet there doesn't appear to be a way to control the current output so it's largely a matter of if the device can start up and achieve regulation within a short enough period to use PWM. The datasheet doesn't seem to supply that information and doesn't give any hints to how the internal control circuit operates so it may just be a matter of trying it and if doesn't work you may have to replace the driver with a circuit suitable for PWM.