If you own the property, you might was well swap the lamp holder for a standard BC one and buy some LED GLS type lamps. Even a 100W equivalent wont be much more than 13W, which is obviously less than that lamp and will give a better output.
Be wary asking for a DD lamp most people will think you mean a 2D lamp and they will not fit, that holder.
Looks like it is for for what is known as a xxwatt 4 pin PL-C lamp.
They are sometimes known as xx watt DE lamps
Though not necessarily an 18W maybe 10w, 13w hard to tell from the pic, but maybe stamped on the housing somewhere
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