LED light bulb, 470lm/40W Crown E14, from Attralux. If you"re struggling with light bulbs and technical data, here"'s a brief explanation of the most important things you need to be aware of. Today, brightness is measured in lumens instead of watts. You can roughly go by the following. 15W = 140 lumens 25W = 250 lumens 40W = 470 lumens 60W = 800 lumens 75W = 1050 lumens 100W = 1520 lumens In addition, you can also see on a light bulb that there is an RA or CRI value. This is the light"'s ability to reproduce colours and is rated on a scale from 0-100 RA. 100 RA gives the best colour rendering and that"'s what you get from daylight. For a typical home, you should choose light bulbs with an RA value of more than 80. There will also be a kelvin degree labelled. This is the colour of the light. A light bulb with a kelvin rating of 2,700 - 3,000 has a warm light. 4.000-4,5000 gives a neutral to cool light and is the most optimal light colour to work in. If you need extra energy during the dark months, go for a kelvin rating of 6,000 or higher. If you want to read more about light bulbs, you can find more information here.