Lumens vs watts

For about a century, watts worked fine as a brightness proxy. Incandescent bulbs all used the same technology at roughly the same efficiency, so a 100W bulb really was brighter than a 60W bulb, and buying by wattage was buying by brightness without anybody having to think about it.

LEDs broke that. An LED producing the same light as a 60W incandescent draws around 8 watts, and the ratio is not fixed - it improves as the technology does. The EIA has tracked LED efficiency rising steadily over the last decade, which means the wattage that corresponds to a given brightness keeps falling.

So watts now tell you about your electricity bill and nothing about your room. The unit that describes brightness is the lumen, and it is printed on every box.

If you remember one row, make it 60W equals about 800 lumens. That is the anchor most household lighting is built around - the Philips Ultra Definition A19 publishes exactly 800 lm at 2700K with CRI 95, and it is the bulb this site reaches for more often than any other.

"60W equivalent" is a translation offered for your convenience, not a measured property. No two manufacturers have to agree on it, and they do not.

You can see it in the products this site already recommends. The Cree A19 is sold as a 60W equivalent and publishes 815 lumens. The Philips A19 is also a 60W equivalent and publishes 800. Those are close. But the 100W-equivalent Philips publishes 1,500 lm, while other 100W-equivalent bulbs on the market publish 1,600 - a hundred lumens of difference hiding behind an identical claim.

The gap grows at the edges of the range. A Feit R20 publishes 450 lumens, which puts it at 40W-equivalent brightness in a fitting people often expect to behave like a 60W one, because the shape looks like a floodlight.

None of that is dishonest. It is just imprecise, and it is why every recommendation on this site quotes a published lumen figure rather than an equivalence.

The reason this matters beyond pedantry is that lumens add up and watts do not.

If you know a room has four fittings and each holds an 800 lumen bulb, the room has 3,200 lumens in it. You can compare that against a target, and you can change the answer by changing bulbs. That whole method - floor area multiplied by a published illuminance range - is set out in how many lumens does a room need, and it only works because lumens are additive.

It also gives you the cheapest fix in home lighting. Reading the figure on the bulbs you already own frequently reveals that a dark room is full of 450 lumen bulbs, and that swapping them for 1,500 lumen bulbs adds thousands of lumens for the price of a multipack, with nothing to install and no cord to route.

One caveat worth carrying: lumens describe what leaves the bulb, not what reaches your book. A shade, a sealed fitting or a narrow beam angle all change the outcome - which is covered in lamp shades and diffusion and beam angle and spread.