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How to keep a non-stick pan alive
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Articles
2 min read
Switching to LED: what the numbers on the box mean
Three numbers appear on an LED box, and only two of them matter to most people.
Lumens is brightness. This is the one to look at first, and the one most people ignore because we all spent thirty years buying bulbs by wattage. As a rough guide: 450 lumens replaces an old 40W bulb, 800 lumens replaces a 60W, and 1100 lumens replaces a 75W. A 9W LED putting out around 800 lumens is the standard household replacement.
Watts is electricity used, not brightness. On an LED it is only useful for working out running cost. The reason a 9W LED replaces a 60W incandescent is that the old bulb spent most of its energy producing heat rather than light.
Kelvin is colour temperature, and it is the one people get wrong. 2700K is warm and yellow, like the old bulbs, and suits living rooms and bedrooms. 4000K is neutral white, good for kitchens and bathrooms. 6500K is daylight, which is bright and slightly blue and belongs in a garage or a workshop, not above a dining table. Mixing temperatures in one room looks like a mistake even when people cannot say why.
On cost, the arithmetic is unusually clear. A 60W bulb left on five hours a day uses about 110 kWh a year. The 9W equivalent uses about 16. Multiply the difference by your rate and by the number of bulbs in the flat, and the replacement typically pays for itself inside a year even before you count not replacing burnt-out bulbs.
Two practical notes. Check the fitting before you buy: E27 is the common screw fitting, B22 is the bayonet, and they are not interchangeable. And if a fixture is on a dimmer, buy bulbs marked dimmable, or they will flicker and buzz.
Lumens is brightness. This is the one to look at first, and the one most people ignore because we all spent thirty years buying bulbs by wattage. As a rough guide: 450 lumens replaces an old 40W bulb, 800 lumens replaces a 60W, and 1100 lumens replaces a 75W. A 9W LED putting out around 800 lumens is the standard household replacement.
Watts is electricity used, not brightness. On an LED it is only useful for working out running cost. The reason a 9W LED replaces a 60W incandescent is that the old bulb spent most of its energy producing heat rather than light.
Kelvin is colour temperature, and it is the one people get wrong. 2700K is warm and yellow, like the old bulbs, and suits living rooms and bedrooms. 4000K is neutral white, good for kitchens and bathrooms. 6500K is daylight, which is bright and slightly blue and belongs in a garage or a workshop, not above a dining table. Mixing temperatures in one room looks like a mistake even when people cannot say why.
On cost, the arithmetic is unusually clear. A 60W bulb left on five hours a day uses about 110 kWh a year. The 9W equivalent uses about 16. Multiply the difference by your rate and by the number of bulbs in the flat, and the replacement typically pays for itself inside a year even before you count not replacing burnt-out bulbs.
Two practical notes. Check the fitting before you buy: E27 is the common screw fitting, B22 is the bayonet, and they are not interchangeable. And if a fixture is on a dimmer, buy bulbs marked dimmable, or they will flicker and buzz.
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