Most floor lamps look good in a showroom. The trouble starts at home, when the shade lands at eye level, the bulb throws a hard white glare across the sofa, and the only switch is a rocker on the cable tucked behind the armchair. None of that is bad luck. It comes down to four decisions that are easy to get wrong: the size of the shade, the bulb the lamp is designed for, where the switch sits, and how the lamp's scale relates to the room around it. Get those right and a floor lamp stops being an object you notice and becomes light that simply works.

Start with scale, not style

Floor lamps live in the space between the floor and everything else: the arm of a sofa, the back of a reading chair, the edge of a picture rail. If the top of the shade finishes below the back of your sofa, the lamp will look as though it has sunk into the carpet. If it towers over a low armchair, it will dominate the corner.

Measure two things before you shop: your ceiling height and the height of the furniture the lamp will sit beside. In a room with a standard 2.4-metre ceiling, a lamp around 150–165cm tall tends to sit comfortably. Period houses with high ceilings will take 170–180cm, or an arc lamp that reaches out over a seating area. Look at what is already in the room, too. A floor lamp standing at exactly the same height as a pendant or a wall light creates a busy, flickering look. Slight variation reads better than matching.

Shade size decides whether you see the bulb

The most common mistake is a shade that is too short or too narrow for the height of the lamp, leaving the bulb visible from a seated position. When you sit in the chair the lamp is meant for, the bottom edge of the shade should sit at roughly eye level or slightly above it, so the light falls on a book rather than in your face. If you want the light lower, choose a shade with a diffuser panel underneath or one made from a denser fabric.

Width matters just as much. Floor lamp shades usually measure somewhere between 35cm and 45cm across; narrower than that and the lamp looks spindly, wider and it starts to feel top-heavy. As a rough guide, the shade should be clearly wider than the widest part of the base, so the whole thing looks balanced. Then consider the material. An opaque shade with a closed top throws light both up and down, which is lovely for atmosphere. A linen or cotton drum spreads a soft, even glow. Metal and glass give a sharper, more directed pool of light.

The bulb is half the lamp

Bulb choice is where floor lamps quietly fail. Check the fitting before you fall for the design. E27, also sold as ES, is the most common fitting in UK floor lamps. E14, or SES, is smaller and appears on slimmer designs. Some lamps use integrated LEDs that cannot be replaced, which is worth knowing if you might want to change the colour of the light later.

Check the maximum wattage on the label, usually inside the shade holder or under the base. It matters even with LEDs, because the fitting and wiring are only rated for so much.

• Dimmable lamp, dimmable bulb. A standard LED on a dimmer will flicker, buzz or refuse to dim at all.
• Colour temperature. Around 2700K gives the warm light most people want in a living room; 3000K is a little crisper; 4000K and above tends to look clinical at home.
• Brightness. Think in lumens rather than watts, and match it to the job. Ambience needs far less than reading.
• Bulb shape. A long bulb in a shallow shade will poke out of the bottom or leave a bright hot spot near the rim.
• Enclosed shades. Fabric and glass shades trap heat, so check the bulb is rated for enclosed fittings.

Where the switch sits

Think about the moment you will actually use it: sitting down, in the evening, with a cup of tea. An inline rocker on the cable means bending to the floor, and if the lamp stands behind a sofa you will be reaching blind. A foot switch is easier, provided the lamp is not tucked behind furniture or sitting on the far edge of a rug you walk across. Switches mounted on the bulb holder at the top look elegant but require reaching over or past the shade. Touch dimmers let you change the mood without getting up, though they can be fussy about which bulbs they will work with.

Count the cable, too. Most floor lamp leads run between about 1.8m and 2.5m, which is shorter than people expect. Measure from where the lamp will stand to the nearest socket before buying. A switched socket is genuinely useful; if yours is not switched, a smart plug gives you control without crawling behind the sofa. Bear in mind that smart bulbs need the lamp left switched on at the wall to work.

A five-minute check before you buy

1. Measure the ceiling height, the height of the chair or sofa arm, and the footprint the base needs.
2. Stand where the lamp will go and note what else is lit in the room.
3. Sit in the chair and picture the bottom of the shade at eye level.
4. Find the nearest socket, check whether it is switched, and work out the cable distance.
5. Confirm the fitting, the maximum wattage and whether the lamp is dimmable, then buy the bulb with it.
6. Test the base. A heavy base on a wobbly three-legged frame will still wobble. On thick carpet or uneven boards, a flat weighted base is safer.

The lamp you stop noticing

A floor lamp that works is one you never think about. It stands at the right height beside the chair, the shade keeps the bulb out of your eye line, the light is warm enough to sit under all evening, and the switch is where your hand expects to find it. Get those four things right and the style question becomes easy, because most designs will do the job. Get them wrong and no amount of attractive detailing will stop you reaching for the ceiling light instead. Measure first, buy the bulb with the lamp, and spare ten minutes to imagine reaching for the switch while you are sitting down.