A table lamp beside the sofa can feel soft and warm, or it can feel like a small spotlight aimed at your face. The difference is often not the lamp itself but its height. The rule of thumb that designers repeat is simple: when you are sitting, the bottom edge of the shade should be at about eye level, or a little below it. It is a guideline, not a law, so the planner below lets you see why it works and where it stops working.
Seated eye height is measured from the floor to your eyes while you sit. Typical published averages are around 115–125 cm. The shade is drawn 22 cm tall and the lamp sits about 90 cm from your eyes, like a lamp beside a sofa arm.
A bulb is the brightest thing in the lamp. A shade exists to hide it and spread its light softly. When the bottom edge of the shade is higher than your eyes, you look up into the opening and see the bulb itself. Your eyes then adjust to that bright spot and the rest of the room looks darker and more tired. When the shade bottom is at or just below your eyes, you see only the glowing shade, and the bulb stays out of sight.
The other direction is not a disaster, only a different feeling. A very low lamp pours its light onto the table and the floor around it. That can be lovely for a quiet corner, but it is weak for reading and it leaves the wall behind you dark. That is why the planner calls it "low" rather than "wrong".
You can measure it in a minute. Sit the way you normally sit on that sofa, relax, and ask someone to measure from the floor to your eyes. Published tables of average adult dimensions put seated eye level at roughly 115 to 125 cm from the floor on a seat about 44 cm high. A deep, low sofa lowers it and a firm dining-style chair raises it. People also sit differently from one evening to the next, so use a typical number and don't chase the last centimetre.
The sum to do: table height plus lamp height minus shade height is where the bottom of the shade ends up. Compare it with your eye height. Aim for the same number, or up to about 20 cm lower.
You rarely need to buy anything. A lamp that is too tall can move to a lower table, a stool or the floor. One that is too short can stand on a stack of hardback books, a wooden box or a small tray. Make sure whatever you use is stable and can't tip, and keep a bulb in it that is within the maximum wattage printed on the lamp. Swapping the shade for a deeper or shallower one also changes where the bottom edge lands. Second-hand lamps and shades are a good place to experiment because the cost is small.
The rule is written for a lamp you sit beside and glance at. For reading, you want the light to fall on the page, so an adjustable lamp or a lower shade pointed at your lap can serve you better. In a room where you mostly stand, such as a hallway or kitchen corner, a taller lamp is fine because nobody looks up into it. Shades with a closed top and bottom, or very deep shades, hide the bulb better than shallow ones. A dimmer or a softer, lower-lumen bulb takes the edge off a lamp that sits slightly high. If the lamp feels comfortable to you, it is the right height, whatever the number says.
Take your table height and seated eye height with you, or note them on your phone. Look for listings that give the shade height as well as the total height, check the socket type matches the bulbs you already own, and don't be afraid to ask a shop about a dimension that isn't listed. Cosy comes from a few warm light sources at different heights, and each of them can be a lamp you already have.