Checking how much of your meter reading goes on lighting

Rather than guessing from the bill, use the meter reading and its pulse light to measure what your home lighting actually consumes.

When the monthly electricity bill arrives, lighting is often the first suspect: "the lights are on everywhere, that must be where the money goes." Usually that stays a hunch. Yet the meter on your wall can tell you how much energy the lighting really takes. You need no special equipment, only a little patience, a pen and the right order of steps.

What the meter actually shows

A household meter adds up energy in kilowatt-hours (kWh). One kilowatt-hour is 1,000 watts running for one hour: a 10-watt bulb, for example, uses one kWh after 100 hours. The number on the display or dials is a running total since the meter was installed, so consumption is always the difference between two readings.

Most electronic meters also have a small flashing light, the pulse indicator. Next to it you will see something like "imp/kWh", for example 1600 or 3200. That tells you how many times the light flashes for every kilowatt-hour that passes through. This little light is what lets you measure power in just a few minutes.

Method one: counting pulses

This takes a few minutes and gives you the power drawn by a particular group of lights.

• Switch off as much as you can: fridge, air conditioner, water heater, anything charging. You can unplug the fridge briefly, just remember to plug it back in.
• Watch the pulse light. If it still flashes, there are background loads (router, TV on standby); count their rate first.
• Now switch on only the lights you want to test and count the pulses for one minute.
• Work out the power: watts = pulses per minute × 60 × 1,000 ÷ the meter's imp/kWh figure.

An example: the meter says 3200 imp/kWh and with the chandelier on you count 3 pulses a minute. That is 3 × 60 × 1,000 ÷ 3,200 ≈ 56 watts. If the background load was 1 pulse a minute, subtract it and the lights account for roughly 37 watts. Low-wattage LED lamps produce sparse pulses, so for accuracy count over 3–5 minutes and average.

Method two: comparing two readings

On older meters without a pulse light, or when you want a picture of a whole evening, comparing readings works well. Note the reading before the lights go on in the evening and again before bed. The next day, use as little lighting as possible over the same hours and repeat. If the other appliances ran roughly the same way, the difference between the two evenings is close to what the lighting used.

The weakness of this method is that kettles, washing machines and air conditioners also run in the evening and easily drown out the lighting. On test days try to use them the same way, and repeat the comparison more than once.

Making sense of the result

Multiply the measured power by the hours of daily use to get real consumption. A 56-watt chandelier on for 5 hours every evening uses about 0.28 kWh a day, or 8–9 kWh a month. Compare that with the monthly kWh on your bill and the share of lighting becomes obvious.

The measurements sometimes surprise people:

• A small gap between the wattage printed on the bulb and the measured figure is normal; an LED lamp's driver uses a little energy too.
• If pulses continue with a lighting circuit switched off, suspect an illuminated switch, a smart relay or a transformer left connected.
• If one room comes out higher than expected, check whether an incandescent or halogen bulb is still hiding there.

Staying safe while you measure

There is no need to open the meter cover, touch the seal or handle any wiring: everything can be read through the window. If the meter is in a shared stairwell, your neighbours' consumption does not affect your figure, since each flat has its own meter. If you want to isolate circuits by switching off breakers in the consumer unit, keep your hands dry and label which breaker controls what before you start.

Should the meter readings persuade you to change bulbs, look up which wattages Zəfər İşığı LED lamps come in, then feed your own numbers into the site's savings calculator to see the yearly difference.