These lamps are commonly found in downlighters, they are quite powerful low energy lamps with a very long life
They need the correct lampholder and you cannot change from one wattage to the another easily
The wrong lamp will not go into your fitting because they have plastic flanges which prevent this, if you have to force it it is wrong
The wattage is written on the lamp and this and the colour tone is all you need to know to order replacements
They come with either two or four pins. The four pins allow dimming and are used as emergency lighting so if your fitting is also an emergency then the chances are you have a four pin lamp in it. Of course the easiest way to be sure is to take the lamp out and check!