Choosing a bulb: fit, brightness and colour
Start with the fitting, not the wattage. Check the lamp holder and the fixture manufacturer's limits. E27, E14 and GU10 are different cap types and are not interchangeable. Check physical dimensions as well as the cap.
Compare brightness in lumens. Watts describe power consumption, not a universal brightness level: two technologies can draw different power while producing similar light. Do not exceed the fitting's stated limits.
Colour temperature is expressed in kelvin. Lower values generally describe warmer-looking light, while higher values look cooler. Choose deliberately for the room and compare the manufacturer's stated values rather than relying on a product photograph.
Dimming requires compatibility across the bulb, driver and control. A dimmable label does not guarantee compatibility with every dimmer or smart system. Read both manufacturers' compatibility guidance.
Before buying, record the cap type, maximum permitted power, available space, desired brightness, colour temperature and control system. For enclosed fixtures or wet locations, confirm explicit suitability with the manufacturer and a qualified installer.