At the top of this chart you have the brightness of the bulb in lumens. This is the number you need to start thinking in. Let's say you're in the US and want to replace an old 60W bulb and get a similar amount of light.Then you know you'll need to get at least 800 lumens in order to match the brightness of the old 60W.et's say you're in the UK and want to replace an old 60W bulb and get a similar amount of light. Then you know you'll need to get at least 700 lumens to get a similar brightness to the old bulb. Knowing your lumens means you will get the brightness you want, and avoid being mis-sold 'replacement bulbs'.