It takes fluorescent D2 bulb but the variable power ballast is no longer able to light up the bulb. I have tried new bulb but it just keeps on blinking. Googling the ballast and looking at ebay/amazon, I could not find a replacement. If I could put a regular socket there, I can reuse this one rather than throwing it out. I had another one which went bad many years ago and I tried to disassemble it but could not get to the innards.