What’s the difference between Lumens and Watts?

The transition from incandescent and halogen light bulbs to energy-saving light bulbs has been taking place for the past seven and a half years. Beginning in September 2016, the EU directive (EC 244-2009) set out a timetable to phase out these older bulbs in favour of more energy-efficient models to reduce carbon emissions across the EU by an estimated 35 million metric tonnes.

Incandescent bulbs were banned from sale in the UK in 2016, while halogen bulbs followed (except for some specialist applications) in September 2019. It’s not illegal to buy, sell, or use these bulbs, of course, but you’ll be hard-pressed to find them in most shops.

The brightness of older bulbs used to be measured in watts, while many of the newer bulbs measure their brightness in lumens, which can be confusing for anyone used to the older system. But what is the difference? In this article, we’re going to address that question and more.

The difference between watts and lumens

Put into simple terms, watts are a measurement of power, specifically the amount of power consumed by the bulb when it’s in operation. Lumens are a measurement of brightness, describing how much light is emitted by the bulb in question. Back in the day, when everybody used incandescent bulbs, there was no need to also include a measurement of lumens, since the higher the wattage, the brighter the bulb—simple.

These days, it’s not so cut-and-dry. The whole purpose of energy-saving bulbs is that they operate on a lower wattage than incandescent bulbs. A bulb might give off the same amount of light as an old 100-watt bulb, but it only needs 40 watts to run effectively. Even then, there are many new types of bulbs on the market. You could have several that generate the same amount of lumens, but each one requires different levels of wattage to operate.

Lumens and Watts Comparison in Incandescent, LED, and Halogen Lights

So, how do you choose the right light bulbs for your home if watts are no longer a useful form of measurement? In short, you need to look at the lumens figure; this tells you how bright the bulb is. You can get a rough comparison to the brightness of old incandescent bulbs with the following table:

40W = 450 lumens
60W = 800 lumens
75W = 1100 lumens
100W = 1600 lumens
150W = 2600 lumens

This means that if you’ve used up the last of your stock of 100W bulbs and you need an LED bulb that offers a comparable level of brightness, you need to find one that produces 1600 lumens.

You will see that energy-saving bulbs still include a measurement in watts. While this is no longer useful for estimating brightness, it still has its uses. The lower the wattage, the more energy-efficient the bulb is. By comparing the lumens to the watts, you may be able to find yourself the best bulb for lighting your rooms and saving you money at the same time.

How many lumens do I need for each room in the house?

Of course, that’s all well and good, but it doesn’t help you decide just how much light you need for a given room. While that decision will be largely down to personal taste and comfort, there are some general rules of thumb that can help you.

First, you need to measure the area of your room in square feet. Assuming a roughly rectangular shape, this requires multiplying the length by the breadth. So, a bedroom that’s 13’ long and 9’ wide will have an area of 117 sq ft (13 x 9 = 117). 

Next, you decide on the “foot candle” of your room. Not all rooms require the same amount of brightness, and the foot candle determines this. For instance, sitting (living) rooms, dining rooms, and bedrooms generally need a lower level of brightness—typically 10–20 lumens per square foot. Using the bedroom that we gave as an example above, that would need 1170–2340 lumens to light comfortably.

Other rooms, such as your kitchen, office, and bathroom, need more light, with 70–80 lumens per square foot being a reasonable level. For an 8’ x 8’ (or 64 sq ft) kitchen, that would mean between 4480 and 5120 lumens. This is usually achieved with multiple bulbs fitted at strategic points across the kitchen.

With sheds and garages, it’s a little trickier. If you just need it to be able to see things in the dark, a foot candle of 10–20 lumens is fine. If you regularly work there, you will need closer to 70–80 lumens to take full advantage.

Watts vs. Lumens: Final Thoughts

Getting the lighting right in your home is as much about the positioning of your light bulbs as it is about their brightness. As domestic electricians, we install light fittings in homes across Leicestershire, Derbyshire, and Staffordshire. We operate from our Ashby-De-La-Zouch office, covering a 30-mile radius across the East Midlands.

Call the team today on 01530 441 878 or send an email to info@aandj-bartlett-ltd.co.uk to discuss your lighting needs and see what we can do for you.

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