Five tips for choosing the right Light Bulb

The light bulb market has gone through enormous change since traditional incandescent bulbs were removed from the market and replaced with energy-saving bulbs. Below, we walk you through what you need to know to buy the best bulb for your needs. Once you've narrowed down your choice of size, type and brightness, head to our reviews section where we reveal the best and worst light bulbs.

1) What fitting do you need?

There are an awful lot of fittings to choose from so, if you can, it's best to take the old bulb you are replacing to the store with you. But if you can't do that, then use the graphic to the right which shows some of the most common fittings. You will need to write down the fitting reference number and take it along to match with the packaging on the box of your new bulb.

You don’t need to know what they mean.  But if you scribble down the fittings before you start shopping for bulbs not only will they fit, they’ll be the right voltage too.

2) What shape bulb do you want?

Bulb shape is not just a question of liking the look of a bulb, it is about how it throws light.  The design of the bulb determines what direction the light goes, so you need to consider what you want the bulb to do.

Each of the different shapes provides a slightly different spread and angle of light, from the almost 360 degree spread of a globe or golf bulb, to the narrow beam of a spotlight. The 'right' shape of the bulb and spread of the light is essentially down to your personal preference, but do consider how the bulbs will look when they are switched off as well as on and whether they will fit sensibly in their chosen location. For example, you wouldn't want a large stick shape if it will protrude from the top of your bedside lamp.

See the graphic below for the most common shapes.

3) What the right light bulb brightness and colour it need to be?

Decide what type of light you'd prefer. This breaks down simply into brightness, otherwise known as watts or lumen output; and the colour of the light, measured on the Kelvin scale.

Watts and lumens (brightness)

In the past, when nearly everyone filled their homes with incandescent bulbs, brightness was measured in watts - which is actually a measure of power. Since the introduction of energy-saving bulbs this is a less useful measure of brightness as new bulbs use a lot less power to produce the same amount of light. So, instead, light output is measured in lumens. The higher the number of lumens, the brighter the light.

Use this chart to see equivalent watt and lumen output for old-style incandescent and the three-types of energy-saving bulbs (LEDs, halogens and CFLs).

As a rough guide, around 400 lumens would be suitable for a bed-sized table lamp, whereas you might want between 1,500 and 3,000 lumens in total (from more than one bulb) for a good-sized living room.

Now you have decided on how bright you want your bulbs, you need to decide on the colour of the light.

Kelvin scale (colour of light)

Many of us have felt the sinking feeling of getting a new bulb home, switching it on and being bathed with a stark white or bluey light that's more akin to a trip to A&E than a warm cosy living room.

The colour of light is measured on the Kelvin scale, which is actually a measure of temperature. This is why light bulb manufacturers often refer to 'colour temperature' on the packaging. Now we don't need to get into the ins and outs of the Kelvin scale in this guide, save to say that the numbers you see on the side of the bulb packet denote the colour of light that the bulb will emit.

Most people have become used to the warm yellowy light given out by the old incandescent bulb, which is 2,700 on the Kelvin scale. Midday sunlight is about 5,500k, sunset or sunrise lighting is around 2,500k and a candle is around 1,600k.

The colour of light can impact everything, from your mood to the colour of the vegetables on your chopping board, so it is important to get the colour of light that you prefer. Use the picture below to match the Kelvin scale rating with the colour you are after and go armed with this when you head out to buy your bulb.

CRI value

To complicate matters further, each bulb is given a CRI score. CRI stands for Colour Rendering Index and is a measure of the ability of a light source to accurately represent different colours. Put simply, you want to make sure you get a bulb that makes your tomatoes look red, rather than a strange orangey colour.

Traditional incandescent and halogen bulbs are near perfect and score in the high 90s. LEDs and CFLs are a little behind this and are more likely to have a CRI value in the mid 80s. 80 is considered an acceptable level, although like many things it comes down to personal preference.

4) Are LEDs good value yet?

There are three main types of regular light bulb - CFLs (compact flourescent lamp - the standard type of energy-saving light bulb), a halogens or LEDs. For a detailed explanation of each of these bulbs and their pros and cons, see our individual guides and reviews of LEDs, halogens and CFLs.

For a quick guide, below is a summary of each and how much a typical 700+ lumen bulb might cost you per year if you have it on for around three hours a day.

CFL – annual running cost €2.61

CFLs are cheap and widely available in a range of sizes and outputs. Some older CFLs were slow to brighten but this has improved considerably in recent years. They are four times more efficient than incandescent bulbs and quickly pay for themselves in energy savings  – but not everyone likes the light they emit.

Halogen – annual running cost: €10.78

Light from a halogen bulb is similar to an incandescent in colour and quality, as both use a tungsten filament. There’s little difference between the two in the amount of energy used and halogen's are significantly more expensive to run than other energy savers. With an expected life span of less than two years, a halogen bulb is unlikely to pay for itself before it fails.

LEDs – annual running cost: €2.20

These use almost 90% less energy than a traditional incandescent, making them the most energy-efficient type of lighting. LEDs are expensive to buy, but should last up to 25 years. In the long term they are the cheapest option. An LED could save you more than €200 in energy use over its lifetime, compared with an old-style incandescent bulb.

5) What is the best quality bulb for your needs?

Hopefully you are now feeling a little more informed and you have made all of the key decisions. You know the fitting to look for on the box, the shape of bulb, the light colour and brightness to look for and the benefits and drawbacks of a CFL, an LED and a halogen.

You can now head to your our DIY store armed with the correct information – but before you head off, take a look at Best Buy recommendations of the best bulbs in each category. Our reviews of both spotlights and conventional bulbs reveal not only the best but also the ones to avoid - and there's a big difference between the two.

The best bulbs brighten up quickly, don't lost light over time and provide a lot of light for a small amount of power. The worst will add to your energy bills, don't last as long as our Best Buys and don't match the Kelvin and lumens stated on the box.