LED lamp keeps glowing when dimmer is turned off
First and foremost, absolutely required: this has to be inside a steel box.  No plastic boxes.  The metal box needs to be grounded. This will keep containment on a variety of problems. 

Thermal calcs can be quite complicated so I like to shortcut them by leaning conservative.  Everything in modern mains wiring is rated at 60C.  I assume ambient is about 30C.  So I'm looking for a solution that will give about a 20-25C rise.  

Power resistors are real fond of giving 180C or even 350C rise at full rating.  Going "I'll derate by 30% and that'll be good" is a noob mistake. I've had to use a 1000W resistor to get an acceptable rise at 230W. 

Also using a resistor like the anodized aluminum types which require a heat sink, is inappropriate unless you attach it to a heat sink.  They have favorable thermal ratings, but only with the heat sink. Junction boxes are not listed to be heat sinks. 

Experience led me to an Ohmite L25 series with lugs. The data says we'll have just shy of a 20C rise at 1.44W and that will be fine.  The lugs will allow crimp lug attachment with #6-32 or 8-32 screws.