Standard classic bayonet fitting (B22) so a straightforward easy replacement for older incandescent 100watt bulbs. Using energy-efficient LEDs they are equivalent to 100watt(incandescent) bulbs but only consume 13watts, so an immediate 87% saving on your lighting costs. Being LED they should also last a lot longer.
I was aware that these bulbs are not dimmable, but when I replaced a hallway light which has an auto-sensor/switch which turns on/off the bulb when movement is detected during darkness — the bulb would come on fine, but rather than go off it would remain on with a very dim light. This may be an issue if using the bulb on PIR activated lights(?)
I’d give 4.5 stars if I could: but very happy with purchase – cost and functionality, so giving 5.