I set out to upgrade the 921 incandescent bulbs in my 26BH a few months ago and after some trial and error with a few different style LEDs, I'm pretty content with some panels Threebutchers recommended.
I tried some small, cheap cob style bulbs but with only 13 SMD (surface mounted diodes) on them, they were useless as a task or general use light because of their low output but I'm keeping them to use as nightlights for my kid's bunk area. Next, I tried a few 36 SMD panels and they seem OK for use above the bed for reading but still don't have the lumen output as the 921's. Finally, after trying these 48 SMDsthese
I'm happy with them even though the output maybe slightly less than the 921s. These lights are listed as a warm 3528 (3.5mm x 2.8mm), 48 count SMD panel. I may buy a few 5050 (5.0mm x 5.0mm) 48 count SMD panels to so see if there is much of a difference in the lumen output.
As others have reported, the adapters on these imports are a bit picky; they take a bit of force to push in and don't always make a good connection so you may have to straighten the wires to make them work. The lights are also polarity sensitive. I put the adapter in the socket first and then connected the light to the adapter and ignored matching the wire colors on some of the lights. The adhesive tape on the back of the panels are "iffy" substitutes of the real 3M product but it will initially work. Also, I did not notice any radio interference (FM) with these unregulated panels as some have reported.