Smart home gadgets are becoming increasingly popular: heating systems, security cameras and even coffee machines. You can buy smart light bulbs which can be turned on or off from your phone - anywhere in the world. These are all well and good, but they're not going to save you any money. If that's your priority, it's time to replace all the old, inefficient bulbs in your home.

LED bulb buyer's guide: the basics

Compared to traditional incandescent bulbs which were - and still are - used in everything from ceiling fittings to angle-poise lamps, LED bulbs consume at least 80 percent less power.

They may still be more expensive to buy, but over their lifetime - somewhere between 20,000 and 30,000 hours - they could save you several hundred pounds per bulb.

To replace every single bulb in the average home would cost hundreds of pounds, so it's worth figuring out which are the most inefficient (and which are those you use most) and replacing those first. It isn't worth replacing a power-hungry bulb in your shed if you only use it for a few minutes each week. Similarly, if you've already fitted energy-saving compact fluorescent bulbs, it may not be worth replacing these with LED bulbs: always check the wattage of the bulb already fitted to see how much you'd save.

By contrast, you might have a dozen spotlights in your kitchen which you use for several hours per day. These are the prime candidates for replacing with LEDs.

In many cases, it's as simple as removing the existing bulb and fitting an LED bulb. But for certain types of bulb, you'll need a transformer or LED driver as they won't work on mains voltage.

We'll take each type of bulb in turn and explain how you can replace them with LED versions which will use a tiny fraction of the power.

Incandescent

The most recognisable type of bulb, and the easiest to replace. Let's say you have a standard 60W incandescent bulb which you use to light your lounge and replace it with a 12W Verbatim LED bulb. This is overkill, if anything, as the replacement will be noticeably brighter (producing 1,100 lumens - the equivalent of a 77W incandescent bulb and representing 84 percent energy saving).

Using some average figures - 15p per kWh of electricity - you'll save around £3 per year.

It will take a little over five years before you break even (the bulb costs £16 from Amazon), but the bulb will last almost 70 years and therefore save you £236 overall.

Of course, you don't need to spend £16 per bulb - alternatives are available from Amazon, Screwfix, CPC and many other retailers for considerably less. Buy more than three LAP warm white E27 bulbs and they will cost you only £6.64 each from Screwfix. These 10W bulbs are the equivalent of a 60W incandescent bulb and output 810 lumens.

They're said to last for 25,000 hours - the same as the Verbatim - and you'll break even in roughly two years.

LED bulb buyers guide

There are various types of incandescent bulb. The common version - in the photo above - is an E27 screw, but it can also have a traditional bayonet fitting. Most LED bulbs offer a choice of either fitting.

You may also have R50 spotlight bulbs (also known as SES or E14) in ceiling light fittings. These are fairly widely available as LED versions.

However, using the same SES / E14 screw fitting are many 'candle' bulbs. Again, these are easily available in LED.

Halogen

All of these are inefficient and can be replaced with LEDs. Halogen spotlights are perhaps the worst culprits as although they use less power than incandescent bulbs, they're rarely used singly. Typically there will be up to six or eight per room, and if each is a 35W lamp, that's between 200 and 300W. Halogens are notoriously inefficient, such that you can buy 'energy-efficient' halogen bulbs, but even these save only around a third.

LED bulb buyers guide

Halogens come in two main types: GU10 (mains voltage) and MR16 (low voltage - 12V). Just because some are low voltage doesn't mean they use less power. They don't.

Don't forget your outdoor lighting. Halogen floodlights - which have lamps which consume between 120 and 500 watts - can be replaced with 10- or 20W LED versions for around £10 to £20 per light: you replace the entire light fitting. This 10W model costs only £9.98 from Toolstation.

LED bulb buyers guide

Fluorescent

Fluorescent strip lights are typically found in the garage or under kitchen cupboards. They have been around for decades, and were considered energy efficient until LED came along. You can't buy replacement LED bulbs for fluorescent tubes. Instead you can replace the entire light fitting with an LED strip.

The strips themselves are cheap - under £10 for a 5m roll on ebay - but you'll need a 12V power supply as you can't connect them directly to the mains. Some kits come with a mains adaptor which you plug into a wall socket, but if you want to turn your lights on using the wall switch for your old fluorescent lights, then you need to buy an LED driver which can be connected to the mains wiring that was powering the old strip light.

Drivers cost a few pounds each, and you should get one capable of outputting 10-12W per 5m strip of LEDs.

LED bulb buyers guide

In terms of the LED strips, there are two types: waterproof and non-waterproof. Go for the latter if they will be installed anywhere they might be splashed with water.

There's also a choice of LEDs. The best for most applications is SMD5050 which is brighter than the SMD3528 alternative. The numbers are the dimensions of the LEDS: 5.0x5.0mm and 3.5x2.8mm.

Finally, there's a choice of colour temperature. Most people will prefer warm white, which is most similar to existing fluorescent lighting. Cool white gives a bluer light which a lot of people dislike as it has a cold, clinical look.

LED bulb buyer's guide: how to choose an LED bulb

Before you head off to ebay and buy a bunch of super-cheap LEDs from China there are a few things to consider: brightness, warranty, beam angle and more.

When shopping, it's sensible to stick to well-known brands and avoid no-name cheap deals. However, that's not to say you shouldn't buy a no-name bulb. If you buy it from Amazon, Wilkinsons or even Lidl or Aldi, you can at least keep the receipt and get a refund or make a warranty claim. But you'll struggle to do the same if you've bought off ebay from a seller in China.

User reviews can be helpful as well, as people will often share their long-term experiences with bulbs from, say, Amazon.

Also, bear in mind that an LED bulb contains electronics as well as the LED itself. The electronics are arguably more likely to fail than the LED. This explains the slightly strange situation where manufacturers claim their bulbs will last 25,000 hours yet only offer a three-year warranty. If the unit fails after that, you've no comeback, so don't pay over the odds unless you find an even longer warranty.

When it comes to the bulbs themselves, here's what to look out for:

Dimmable

Not all LED bulbs are dimmable. In fact, expect to pay more for dimmable bulbs and don't try and use non-dimmable models with a dimmer switch. It can be cheaper and easier to replace the dimmer switch with a standard wall switch.

Colour temperature

Colour temperature is crucial: most people prefer the warm white, which is very similar to halogen, rather than the 'cold' bluish tint of white or cool-white LEDs. Look out for the actual colour temperature in Kelvin: 2700-3000K is a good warm white. Higher values, say 5000K or 6000K will look cooler. If you want a whiter look, be careful as you can end up with a very clinical look.

Brightness

You also need to look at brightness, measured in lumens. Try to find out how many lumens your current halogen lamps produce, and match or exceed that. Some cheap LED bulbs produce as little as 120lm, but you'll probably find you need 350-400lm to provide the same light output as your existing bulbs.

Beam angle

Next up is beam angle. This determines the spread of light the bulb produces. A narrower angle means light will be concentrated on a smaller area, like a spotlight. A larger angle is better for lighting a larger area, but don't forget this means it could appear dimmer overall. For replacing Halogen downlights, look for a beam angle of around 40 degrees. Incadescent replacements should have a much larger beam angle, say 140 degrees.

CRI

CRI is another spec you should see (if you don't, it's worth asking for the CRI figure). Here's why: CRI stands for Colour Rendering Index and is a measure of the light quality from 0 to 100. In other words, the CRI score tells you if objects appear the correct colour when lit using that bulb. Incandescent bulbs had a brilliant CRI, but not so with fluorescent tubes. If you want to avoid bad-looking lighting, it's crucial to go for LEDs with a high CRI.

Technology

Not all LEDs use the same technology. Cheaper bulbs will tend to use multiple SMD (surface-mount device) LEDs, but newer or more expensive ones will use COB - chip on-board LEDs.

COB offers a higher light output per watt, and tends to be used in smaller bulbs such as MR16. COB isn't necessarily better than SMD, though. It depends on the form factor of the bulbs you're buying and your priorities in terms of budget.

Existing equipment

If you are replacing low-voltage halogen bulbs, there are no guarantees that LEDs will work on your particular transformers which may require a minimum power draw to work properly. If the draw is too low from your super-efficient LED bulbs, they may flicker or not work at all. In this case, you would need to either replace the transformers with proper LED drivers, or change the fittings from MR16 to mains-voltage GU10 fittings and buy GU10 LED bulbs instead. Fittings are cheap, and it may be cheaper to go down this route than buy an LED driver for each MR16 bulb.