Posted on 27th March 2018

Guide to Energy Saving Light Bulbs

It’s a fact: energy saving light bulbs work. The technology of various low-energy bulbs has developed to the point where homeowners can make consistent savings over months and years without losing any of the lighting quality they enjoy from standard halogen bulbs.

However, there’s no one-size-fits-all bulb that you can buy and expect to work exactly as you imagined. There are different types of low-energy options available, and within these types there are different wattages and even light colours that you can choose from.

If that all sounds a bit overwhelming, don’t worry! We’ve created this guide to help you understand what these different types of bulb are, how much money they could save you and how to make sure you choose the right option for your home.

What are the different types of light bulbs?

There are two main types of energy saving bulb, CFLs (compact fluorescent lamps) and LEDs (light emitting diodes). In this section, we’ll look at how each of these work and, importantly, why they save energy.

The standard, non-energy saving type of light bulb is called a halogen bulb. We’ll start by briefly looking at how it works to provide a point of reference for the two energy saving types.

Halogen bulbs

Halogen bulbs pass a current through a thin tungsten filament to produce light. The tungsten provides resistance to the electricity, which causes it to heat up. When it gets hot enough, it glows with a warm, yellowish light. Halogen gas surrounds the tungsten within the glass casing, which prevents it from blackening and thinning, both of which would cause the light to be less effective.

Simple annotated diagram of a halogen bulb

The reason halogen bulbs are so inefficient is because the majority of the energy used to keep them on is wasted as heat, which is necessary if the metal is going to produce light. With most halogen bulbs, you can physically feel the heat that they’re giving off when you get too close.

CFL bulbs

CFLs (compact fluorescent lamps) are the most common type of standard energy saving bulb. They don’t contain a metal filament like halogens, instead, they contain a transparent glass tube which is filled with argon and small amounts of mercury vapour. Passing a current through this mix of gases causes their atoms to emit small amounts of ultraviolet (UV) light, which is invisible to the human eye. The UV rays excite the atoms in a thin layer of phosphor that coats the glass tube. This causes the phosphor to emit visible light.

Simple annotated diagram of a compact fluorescent lamp (CFL)

It takes a few seconds for the phosphor to produce light at the same levels a halogen bulb can produce, which is why they have a ‘warm-up’ period. Before they get to full brightness, they’re actually less efficient than halogens, but after this point they use a lot less energy, simply because nearly all their energy goes into producing light, rather than heat.

LED bulbs

LEDs have been around for decades, but have only really become a viable competitor to halogens and CFLs in the last few years. While not necessarily called ‘energy saving light bulbs,’ they nevertheless use much less energy than halogens, and can justifiably be considered in this category alongside CFLs.

The inner workings of an LED are hard to explain without boring you with chemistry. Basically, an electric current is passed through a tiny electrical component called a diode, made out of specially treated silicon. When current passes through the silicon diode, spare electrons move from one half to fill empty spaces in the other. When an electron settles into a space, it emits photons – the particles that make up light.

Simple annotated diagram of a light emitting diode (LED)

LEDs only need a small current to produce a lot of light and very little energy is wasted, which makes them much more efficient than halogen bulbs.

Brightness comparison

If you want your energy saving bulbs to replace your halogens properly, you’ll need to make sure they’re the same brightness. However, it’s not as simple as buying the same wattage. As energy saving bulbs use less energy than halogens, they can produce the same brightness at a much lower wattage. Instead, you need to match their lumen output. The chart below is an easy guide to see which wattage you should be looking for in energy saving bulbs in order to match your old halogens.

Chart showing the lumen output of halogen bulbs, CFLs and LEDs at different wattages

Energy consumption and cost

Are energy saving bulbs worth it? Halogen bulbs tend to be the cheapest to buy off the shelf, so do the alternatives save enough money to make them a genuinely cost-effective option? The short answer is yes.

As an example of the difference, we’ve added up the cost of running mid-level, 400 lumen bulbs, equivalent to a 28W halogen bulb, a 9W CFL and a 6W LED. We calculated our figures assuming that the bulb would be used for 5 hours a day, 365 days, with electricity costing £0.18 per kWh.

The halogen bulb is clearly the most expensive, costing £9.20 to run for a year. It’s over three times more expensive than the CFL, which costs £2.96 to run, and over four times more expensive than LEDs, which cost just £1.97.

Let’s put that in context with the base cost of the bulb. An average 28W halogen will set you back about £1.50, whereas a 9W CFL 6W costs about £3.00 and an LED will cost you £4.00. Therefore, the total cost of buying a halogen and running it for a year is £10.70, almost £5 more expensive than the £5.97 cost of an LED and nearly equivalent £5.96 cost of a CFL.

If that wasn’t enough to convince you, you can also factor in the lifespan of the bulb. An average halogen tends to last about two years, compared to the 10-year lifespan of a CFL and the staggering 25-year lifespan of an LED bulb. For a long-term price comparison, we can compare the cost of running these bulbs over the lifespan of the longest: the LED.

To run a single light with halogen bulbs for 25 years, you’ll need 13 halogen bulbs. This costs £230 in electricity – plus the cost of 13 bulbs, which adds up to £19.50 – giving us a total cost of £249.50. Running a CFL for that time would cost a much more palatable £74, which combines with the cost of the three bulbs you would need to give a total of £83. Finally, an LED costs £49.25 to run for that time, and you only need one bulb, which makes the total cost £53.25.

It’s clear that an LED is the best long-term investment. In fact, because of the difference in energy cost, the LED becomes the cheapest bulb as soon as it enters its second year of life and the longer you use one for, the more it will save compared to halogens and even CFLs.

Graph showing the kWh consumption of different types of bulb in a year

CFLs vs LEDs

We’ve established that energy saving bulbs are indeed a better option for your budgets, and certainly a better option for the environment. However, they were not all created equal. While CFLs are a viable option and still preferred by many people, LEDs actually trump them in most direct comparisons.

LEDs become cheaper to buy and run as long as the bulbs last longer than a year and use less energy, which is better for your carbon footprint. They’re also less harmful when they’re disposed of; the small amount of mercury vapour in a CFL is toxic and can be harmful to wildlife when released in landfill.

One area where CFLs had the upper hand over LED bulbs for a while was the quality of their light. For many years, LEDs were only capable of producing a harsh, whitish light that couldn’t match the warmer, yellow tones of a CFL or halogen bulb. This is no longer the case. LEDs can now be manufactured to produce a whole spectrum of light, from bright white-blue to warm oranges and reds. What’s more, they don’t have the warm-up period that CFLs still require.

Ultimately, it’s up to you how you choose to invest. If you know you’re only going to be in a property for a period of a few months, it’s unlikely you’ll see the best value from an LED bulb. However, if you’re looking for a longer term saving, halogens and CFLs will both cost more than an equivalent LED option.

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This guide is not intended to advise you on your personal financial situation. It is providing general guidance only. If you are unsure about a decision or anything mentioned in this guide, you should seek advice from an independent professional.