You’ve found the perfect lamp. It looks brilliant, you’ve decided exactly where it’s going, and now there’s just one small job left: choosing a bulb.

Then you start reading the box.

4W. 470 lumens. 2700K. LED. CRI 80.

At which point, buying a light bulb suddenly feels like it requires a minor qualification in electrical engineering.

It doesn’t. And the number we’re interested in here is actually one of the simplest: lumens.

So, what exactly is a lumen?

Put simply, lumens tell you how bright a bulb is.

You’ll usually see them written as lm on the packaging. The higher the number, the more visible light the bulb produces and, generally speaking, the brighter it will appear.

For years, most of us bought bulbs according to their wattage. We knew roughly what to expect from a 40W, 60W or 100W bulb, so watts effectively became our shorthand for brightness.

The problem is that watts don't actually measure brightness at all. They measure how much power a bulb uses.

That distinction became much more important with the arrival of energy-efficient LEDs. An LED can produce the same amount of light as an old incandescent bulb while consuming a fraction of the electricity, so wattage is no longer a particularly useful way of comparing brightness.

Think of it this way:

Watts = how much energy goes in.
Lumens = how much light comes out.

Much easier.

Lumens vs watts: what should I look for?

If you grew up buying bulbs by wattage, you're certainly not alone. Fortunately, there are some useful rough equivalents.

These are approximate comparisons rather than hard rules, but they're a useful starting point. The Energy Saving Trust, for example, gives around 470 lumens as the equivalent of an old 40W bulb and 800 lumens for a 60W bulb.

And this is where LEDs really earn their keep. You can get that familiar 800-lumen brightness from an LED using considerably less power than an old 60W incandescent bulb.

More lumens aren't necessarily better

It's tempting to assume that brighter equals better.

Not necessarily.

Lighting is as much about atmosphere as visibility. You probably don't want the same amount of light beside your sofa on a Sunday evening as you do above a workbench when you're trying to find the tiny screw you definitely just put down there.

For a table lamp or decorative lamp, you're often trying to create a pool of warm, comfortable light rather than illuminate the entire room.

A lower-lumen bulb can therefore be a great choice for atmospheric lighting, while higher-lumen bulbs make more sense where the light has a practical job to do.

Rather than asking "What's the brightest bulb I can put in this lamp?", try asking:

"What do I actually want this light to do?"

That's a much better place to start.

Don't forget about Kelvins

Lumens tell you how much light you're getting, but they don't tell you what that light will look like.

For that, you'll also want to check the Kelvin (K) rating.

Kelvins describe the colour temperature of the light. Lower numbers produce warmer, more yellow-toned light, while higher numbers move towards a cooler, whiter appearance.

As a general guide:

• Around 2700K – warm, cosy light similar to traditional incandescent bulbs

• 2700–3000K – warm white and a good all-round choice for homes

• 4000K+ – cooler, cleaner white light, often better suited to workspaces and task lighting

The Energy Saving Trust recommends warmer 2700K light for living spaces and bedrooms, while cooler white light can be more appropriate for areas such as kitchens and bathrooms.

For the kind of warm, characterful glow that works beautifully with vintage and industrial lighting, we're firmly fans of the warmer end of the scale.

The bulb is part of the design

There's another reason to think about your bulb beyond simply making sure the room isn't dark.

When the bulb is exposed, it's part of the lamp.

A clear globe, oversized round bulb or vintage-style LED filament bulb can completely change the personality of a piece. Put a stark white bulb into an old industrial object and it can feel strangely clinical; give it a warm filament glow and suddenly all that aged metal, patina and texture comes alive.

That's particularly important with HausKat lamps.

When you've got decades of wear, scratches, tarnishing and beautifully imperfect surfaces to show off, the light shouldn't fight against them. It should bring them out.

What bulbs do we recommend for HausKat lamps?

For most decorative table lamps, we'd suggest starting with a warm LED bulb around 2700K and choosing the lumen output according to where the lamp will live.

If it's primarily there for atmosphere, go softer. If you're planning to read beside it or use it as a more practical light source, go brighter.

And always check the information supplied with your lamp for the correct bulb fitting and maximum permitted wattage.

One useful thing to remember here is that a lamp's maximum wattage isn't the brightness we're recommending. It's an electrical limit for the fitting. Lumens are still the number to look at when deciding how bright you actually want your bulb to be.

In short: forget watts, think lumens

The lighting world has made something very simple sound unnecessarily complicated.

So here's the bit worth remembering:

More lumens = more light.
Fewer lumens = softer light.
Watts = energy consumption.
Kelvins = how warm or cool the light looks.

That's really all you need to make a much more informed choice.

And when you're choosing a bulb for an unusual lamp, we'd always argue that the goal isn't simply to produce as much light as possible.

It's to produce the right light.

Because whether your lamp started life as a French textile bobbin, an old garden sprayer or a piece of forgotten industrial equipment, after surviving for the best part of a century it deserves something a little more flattering than the lighting from aisle seven of a supermarket.

Give old things another life. Just make sure you light them properly.

HausKat — forgotten objects, reworked for remarkable homes.