How much electricity does an LED lamp use?

Consumption is measured in kilowatt-hours: watts times hours, divided by a thousand. A 5 W LED bulb burning four hours a day uses 5 × 4 = 20 watt-hours a day, about 7.3 kilowatt-hours a year — roughly what a water heater uses for two or three showers.

Multiply that by the price of a kilowatt-hour on your bill and you have the yearly cost. For a lamp of this size it lands in the region of one coffee — a year, not a month.

For a similar amount of light, an incandescent bulb draws around 60 W, a halogen around 40 W, and an LED 6 to 8 W. The difference isn't in the light but in the heat: an incandescent turns most of its energy into heat and only a little into light. An LED does the opposite — hence a bill several times smaller for the same brightness.

That heat is also why only LEDs belong in a 3D-printed lamp. The body is plastic, and an incandescent or halogen bulb inside a closed shade produces enough heat to deform it over time. On our lamps that's settled in advance: a warm-white E14 LED bulb comes in the box, so the lamp stays lukewarm to the touch.

At these wattages consumption effectively stops being a criterion — the difference between 5 W and 8 W on a yearly bill is negligible. What matters far more is how much light you get (lumens) and what colour it is (kelvin). So when choosing an ambient lamp, look at lumens and colour temperature, and let the watts go.