How To Choose The Right Light Bulb: A Step-By-Step Buyer's Guide
Article by Ian Cobb, 4/5/22
The light bulb market has gone through enormous changes since traditional incandescent bulbs were removed from the market and replaced with energy-saving bulbs. Because of this, buying a new light bulb is a little more complicated than it used to be. Standing in front of rows of light bulbs or browsing page after page can seem overwhelming, but in this guide we'll help you choose the right bulb based on your needs and brighten up your home in no time.
We've split the guide into several sections, covering the different fittings, shapes, types and colours of bulbs available.
Let's get started.
1. Choose the Right Bulb Fitting:
There is a variety of different light bulb caps or bases. Somewhere on your lamp, light fitting or in its instructions will be the correct bulb fitting that it requires. This section shows most of the popular fittings. Make sure you check this carefully as the wrong bulb cap will not work in your light fitting.
Large Bayonet Cap (B22)
Fit: Push and Twist
Bulbs Commonly Found On: GLS/Standard, Candle, Golfball
Key Feature: 22mm Diameter
Small Bayonet Cap (B15)
Fit: Push and Twist
Bulbs Commonly Found On: Candle, Golfball, Other Small Decorative Shaped
Key Feature: 15mm Diameter
Large Edison Screw (E27)
Fit: Screw In
Bulbs Commonly Found On: GLS/Standard, Candle, Golfball
Key Feature: 27mm Diameter
Small Edison Screw (E14)
Fit: Screw In
Bulbs Commonly Found On: Candle, Golfball, Other Small Decorative Shaped (Please Measure Carefully - Smaller Screw Sizes Are Found)
Key Feature: 14mm Diameter
G4
Fit: Push In
Bulbs Commonly Found On: 12V Capsules
Key Feature: 2 Thin Pins, 4mm Between Pin Centres
G9
Fit: Push In
Bulbs Commonly Found On: 240V Capsules
Key Feature: 2 Looped Pins with 9mm Between Loop Centres
GU4
Fit: Push In
Bulbs Commonly Found On: 25mm and 35mm 12V Spotlights
Key Feature: 2 Thin Pins, 4mm Between Pin Centres
GU5.3 (MR16)
Fit: Push In
Bulbs Commonly Found On: 50mm 12V Spotlights
Key Feature: 2 Thin Pins, 5.3mm Between Pin Centres
GU10
Fit: Twist and Lock
Bulbs Commonly Found On: 50mm 240V Spotlights (Please Note - 35mm, 63mm and 111mm Bulbs Are Also Available)
Key Feature: 2 Thick Pins, 10mm Between Pin Centres
GY6.35
Fit: Push In
Bulbs Commonly Found On: 12V Capsules
Key Feature: 2 Thin Pins, 6.35mm Between Pin Centres
GR8
Fit: Push In
Bulbs Commonly Found On: 240V 2D Compact Fluorescent Lamp
Key Feature: 1 Row of 2 Thin Pins, 8mm Between Pin Centres
GR10q
Fit: Push In
Bulbs Commonly Found On: 240V 2D Compact Fluorescent Lamp
Key Feature: 2 Rows of 2 Thin Pins (4 Pins), 10mm Between Pin Centres
R7S
Fit: Push In
Bulbs Commonly Found On: 78mm, 118mm and 189mm Linear
Key Feature: 2 Ceramic Ends with a 7mm Diameter
S15
Fit: Push In
Bulbs Commonly Found On: 221mm and 284mm Striplights
Key Feature: Bayonet Style Caps Without Lugs on Either End with a 15mm Diameter
G5
Fit: Push In
Bulbs Commonly Found On: 12mm and 16mm Diameter Tubes
Key Feature: 2 Pins on Either End, 5mm Between Pin Centres
G13
Fit: Push In
Bulbs Commonly Found On: 26mm Diameter Tubes
Key Feature: 2 Pins on Either End, 13mm Between Pin Centres
2. Find the Best Bulb Shape:
Now you have your right bulb fitting, you will need to choose the best shape for your lamp or light fitting. Each type of bulb provides a slightly different spread and angle of light, from the narrow beam of a spotlight to the 360 degree spread of a globe or golf ball bulb.
The 'right' shape of the bulb and spread of the light is partly down to your personal preference, but also consider how the bulb will look when it is switched off as well as on, and also if it fits sensibly in your lamp or light. You wouldn't want a large stick shape if it will protrude from the top of your table lamp.
GLS / Standard
This classic pear-shaped bulb is the most common bulb shape, used in ceiling fittings, floor and table lamps, wall lights and many other applications. GLS (General Lamp Service) bulbs are also referred to as A-series bulbs and standard bulbs, and are commonly available with both bayonet (B22 / BC) and screw (E14 / SES and E27 / ES) bases. Dimmable options are available.
Candle
Candle bulbs are flame-shaped bulbs which are ideal for use in decorative light fixtures, chandeliers, wall lights and many other decorative light fixtures. Emulating the shape of a candle flame, they are available in a range of base types including bayonet (B15 / SBC and B22 / BC) and screw (E14 / SES and E27 / ES). Filament LED versions have become increasingly popular in recent years, as they produce an incredibly good likeness to vintage bulbs. Dimmable options are available.
Golfball / Round
These spherical-shaped bulbs are slightly smaller than standard GLS bulbs making them suitable for use in tight fitting spaces. Also ideal for use in table lamps due to their 360° light spread, they are available in both bayonet (B15 / SBC and B22 / BC) and screw (E14 / SES and E27 / ES) base types. Dimmable options are available.
Reflector
Named reflectors as they have a reflective surface which focuses the beam angle forwards, these bulbs are ideal for use in desk lamps, recessed light fittings, spotlights and other decorative applications. Typically reflector light bulbs have a large screw (E27 / ES) base but small screw (E14 / SES) and bayonet (B15 / SBC and B22 / BC) bases are available. Dimmable options are also available.
Spotlight
Spotlight bulbs are designed to brighten specific areas with a targeted, narrow beam of light in a forward direction. Because of this they are ideal for kitchen and bathroom spot lighting, as well as recessed ceiling lights and decorative lighting. They can be found in use throughout the home and all commercial premises. Cap bases include GU10 twist and lock, GU5.3 (MR16), GU4 and GX5.3. Dimmable options are available.
Capsule
These mini two-pronged bulbs are ideal for small light fixtures due to their compact size. This combined with their high brightness means they are typically found in decorative or specialist light fixtures. They are commonly used in kitchen units, display cabinets and many other fixtures that require a small, low-profile bulb. Cap bases include G4, G9, GX6.35 and GY6.35. Dimmable options are available.
Globe
These large round bulbs are most often used as decorative light bulbs, especially in commercial spaces where they provide a bright light and distinctive look. As they are larger than standard bulbs, they are available with only the most common cap types: bayonet cap (B22 / BC) and Edison screw (E27 / ES). Filament LED versions have become increasingly popular in recent years, as they produce an incredibly good likeness to vintage incandescent bulbs.
Pygmy and Appliance
Pygmy bulbs are miniature sized bulbs commonly used in many household appliances such as ovens, cooker hoods, fridges and sewing machines. You'll also find them in Christmas decorations and accent lighting. Their small size means that they're most commonly available with smaller cap types, such as small Edison screw (E14 / SES) and small bayonet cap (B15 / SBC).
2D and Circular
Offering the same brightness as fluorescent and LED tube lights, 2D bulbs are turned into more compact shapes, making them more convenient and easier to install. Also known as Double D bulbs they come with two different cap bases: GR8 which has 2 pins, or GR10q which has 4 pins. Like 2D bulbs, circular bulbs offer the same brightness as standard fluorescent tubes and are also available in 2-pin and 4-pin versions. 2D and circular bulbs are commonly used in low profile, recessed and surface mounted light fittings found in bathrooms, stairwells, corridors, utility areas and bulkheads.
Linear
Linear light bulbs are distinctive for their long, narrow shape and double-ended caps and are also referred to as R7S, because of their ceramic ends with a 7mm contact point. They offer a very bright light and excellent colour rendering. Because of this, linear bulbs are found in flood lights, car and DIY work lamps, security light fixtures and most other weather-protected light fittings. Sizes available are: 78mm, 118mm and 189mm.
Striplight and Tube
Striplight bulbs are found in many homes and commercial premises. These double ended bulbs are commonly used in and around bathroom and shaving mirrors, wall hangings, under cupboards and cabinets. Offering even illumination from end to end, you'll also find them above pictures and paintings. Tube lights are energy-efficient and long-lasting, and like striplights offer even illumination from end to end. They come in various lengths between 2 - 6 feet and in either 16mm (T5) or 26mm (T8) diameters. T5 and T8 tubes are commonly used in offices, shops, warehouses and most other commerical spaces, but can also be found in kitchens, garages and utility rooms.
ST64
These pear-shaped bulbs are elegant and intricate, evoking the exposed look and aesthetic of the Victorian age. Longer and narrower than candle bulbs, they add vintage style to homes, bars, pubs and restaurants with their Filament LEDs and warm glow. They are available with a variety of cap bases and wattages, with dimmable options also available.
3. Choose the Best Bulb Technology:
That old incandescent light bulb you're looking to replace has been phased out, and soon will no longer be available at all. There are now three different types of bulb technology, and here we will explain the differences between them.
Halogen
Identical to Incandescent bulbs in shape and size, Halogen bulbs use up to 30% less energy and last twice as long. With an average lifespan of just 2 years, a halogen bulb also emits a lot of heat, meaning it is unlikely to pay for itself before it fails. The production of most halogen bulbs was banned by the UK government in September 2021*, with the rest to follow in September 2023. So whilst Halogen bulbs may still be available to purchase, they are only available whilst stocks last.
- Value option of the current technologies
- Inefficient running costs (only 20-30% energy saving versus incandescent)
- Short lifetime (approximately 2,000 hours)
- Full brightness instantly
- No harmful chemicals so they are safe for the environment
- Dimmable
- Get hot when used after a period of time
CFL (Compact Fluorescent Lamp)
CFLs are cheap and widely available in most sizes and outputs. Older CFLs were slow to brighten, but this has improved considerably in recent years. CFLs use up to 80% less energy than Incandescent bulbs and quickly pay for themselves in energy savings, but not everyone likes the light they emit. They have an average lifespan of 10 years. As with Halogen bulbs, Compact Fluorescent Helix Spiral bulbs could not be placed on the market* after 1st October 2021, so again are subject to availability.
- Low running costs (80% energy saving over old incandescent equivalent)
- 10x longer lifetime than Incandescent bulbs (approximately 10,000 hours)
- Some can take up to two minutes to reach 100% brightness
- Require careful disposal
- Non-dimmable
- Bulbs tend to be larger than equivalent Incandescent bulbs so may not be suitable for all light fittings
LED (Light Emitting Diode)
The future of light technology, and the one we recommend as your first choice. Whilst they were relatively expensive to purchase a few years ago, mass production has resulted in significantly lower prices in recent years. In fact, a typical 60 watt equivalent LED bulb now only costs around £2-3. With ultra low running costs of up to 90% less than Incandescent bulbs and lasting up to 50,000 hours, a LED bulb can save you over £250 over its lifetime compared to an Incandescent bulb and £180 compared to a Halogen bulb. With a LED equivalent now available in all colours, shapes and sizes and more and more dimmable versions being produced, there has never been a better time to upgrade your bulbs to LEDs.
- Ultra low running costs (90% energy saving compared to old Incandescent bulbs)
- Last up to 30x longer than incandescent bulbs (up to 50,000 hours)
- Full brightness instantly so you don't have to wait for it to illuminate fully
- No harmful materials – easy to dispose of and safe for the environment
- Dimmable options available
- Safe to handle as they're usually made from durable plastic and not glass (excluding decorative options)
4. Find the Right Bulb Brightness:
With classic Incandescent bulbs, brightness was measured in watts. As more than 95% of the power consumed by a typical Incandescent bulb was converted into heat rather than visible light, this wasn't actually the best way to measure brightness as wattage only measured the amount of energy used, not light output. Today the brightness of light bulbs is measured in lumens (lm). Simply, the higher the number of lumens, the brighter the bulb. Despite using very low wattages, LED bulbs are able to emit the same brightness as traditional light sources. To make things easier, most retailers and manufacturers quote an equivalent incandescent wattage so consumers can replace their lights and keep the same brightness.
To help you find how many lumens you'll want from your new bulbs, you can use the chart below:
| 230-375lm | 400-500lm | 700-900lm | 900-1125lm | 1300-1500lm | |
 Standard | 25W | 40W | 60W | 75W | 100W |
 Halogen | 18W | 28W | 42W | 53W | 70W |
 CFL | 6W | 9W | 12W | 15W | 20W |
 LED | 2-4W | 4-6W | 7-10W | 10-13W | 13-18W |
5. Find the Right Bulb Colour:
Finding the right colour of your bulb is almost as important as it is finding the cap fitting. Almost all bulbs give off a white glow, however this can vary from a cosy 'warm white' to a cold 'cool/bright white'. Today's light bulbs are all about warmth, with every bulb having a colour temperature rating. When choosing a new bulb, it is important to take into account the colour temperature as the choice will influence the overall ambience and mood.
Colour temperature, also called Correlated Colour Temperature (CCT), describes the appearance or tint of a particular light. Think of colour temperature like you think of paint, where there are seemingly endless shades of white to choose from. In the same vein, there are a number of different colour temperatures for you to choose from when you're selecting new light bulbs. The colour temperature of a bulb is measured in degrees of kelvin and denoted by a numerical figure followed by the letter 'k' on a scale from 1,000 to 10,000. Unlike measuring temperature in degrees celsius, the warmer a bulb's light is, the lower its temperature will be. A cooler temperature will have a higher value. So if you're looking to replace a traditional Incandescent bulb that has a slightly yellowish glow, you'll need to select a bulb with a warm colour temperature of around 2,700K. At the opposite end of the scale, if you're looking for a bulb for security lighting or displaying paintings or goods where accurate colour reproduction is required, you need to look for one with a cooler shade of white around 6,000 - 7,000K.
Using our colour temperature chart above, you should be able to identify the colour of your current bulbs and find the perfect replacement for your needs. As a general rule, warmer temperatures are more calming, inviting, and relaxing, while cooler colour temperatures are often used to enhance concentration in places like schools or offices. It's worth noting that the colour temperature of a light bulb isn't the same as its brightness. This is measured in lumens, detailed above. No matter what space you're lighting, it's important to balance warm and cool temperatures. Although colour temperature is measured on an endlessly varied scale, there are several standard colour temperatures that most light bulbs are manufactured to. All light bulbs today clearly state their colour temperature, making it easy to find the right colour.
Take a look below at some ideas of when are where to use each colour temperature:
Warm White 2,000-3,000K
- Due to their warm and inviting glow, warm white bulbs are suited to rooms meant for relaxing:
- Bathrooms: Warmer tones can be more flattering on our faces, making the tone of our skin look better.
- Bedrooms: A warmer shade of light relaxes the mind helping us to drift off. Cool, blue light can disrupt our circadian rhythms and negatively affect the quality of our sleep.
- Dining and Living Rooms: Warm light is ideal for ambient lighting. Ideally, combine with a dimmer switch so you can adjust the lighting as appropriate.
- Hospitality and Decorative Lighting: Warm light is inviting and friendly, perfect for dimmly lit restaurants, bars and establishments.
Cool White 4,000-5,000K
- Lacking the warmth of warm white, cold white bulbs emit a crisp, fresh shade that's ideal for more stimulating environments:
- Bathrooms: A cooler light can perk us up in the morning, particularly during the winter months.
- Kitchens: A cooler white can create a more sterile feel which can be desirable in a kitchen, while also complementing the usually understated colour schemes found in them.
- Basements: Ideal for environments without another light source, the brightness of cool white is great where vision is of paramount importance.
- Accent Lighting: Cooler shades of white are ideal for highlighting specific areas or objects, creating visual interest.
- Office and Task Lighting: A colder light can help us concentrate on the task at hand, keeping us alert and increasing our productivity.
Daylight 6,000-7,000K
- The colour of daylight bulbs is similar to the light outside seen on an overcast day, and is ideal for promoting focus and concentration:
- Garages and Workshops: The crisp, refeshing tone of day white offers ideal conditions for working, reading and inspection.
- Display Areas: Offering the very best colour rendering, daylight white is perfect for environments requiring high visual clarity.
- Warehouses: The pleasant and luminous tones produced by daylight create a stimulating and clean-looking environment.
- Security Lighting: The high brightness emitted by daylight white bulbs offers the highest level of security.
6. Other Useful Information:
Colour Rendering Index (CRI)
When choosing a new light bulb, you may or may not want to factor in its Colour Rendering Index. CRI refers to a light bulb's ability to render colours accurately. It is measured as a percentage from 0-100%; the higher the CRI, the better its colour rendering ability. Simply, you may want to make sure you get a bulb that makes your tomatoes look red, rather than a strange orangey colour. This is especially important if you are purchasing accent lighting for displaying artwork, or for work spaces that rely on accurate lighting, such as factory production, printing, photography and design.
It's worth noting that Colour Rendering Index (CRI) is not the same thing as Correlated Colour Temperature (CCT), which describes the appearance or tint of a particular light.
Energy Efficiency Labels and Ratings
While we've covered the running costs of the different types of bulb further up, we'll brieftly explain how to read the energy label printed on the packaging of your bulb, particularly as energy labelling has recently changed. Like all electrical goods, lightbulbs are rated on a lettering scale indicating how energy efficient they are. Because of the constant improvement in energy efficiency, most products under the original label had risen to A+ or A++, and so a rescaling was made in order to make it clearer to the consumer about which are the most efficient products on the market.
Prior to 1 September 2021, light bulbs were rated from A++ (most efficient) to E (least efficient). The new energy labels have been rescaled to a simpler A (most efficient) to G (least efficient) scale. This new system not only makes it easier to know which light bulbs are the most energy-efficient, but it also allows more room for innovation. That's because the current most efficient light bulbs will now be rated as D - G in the new rankings, giving manufacturers the opportunity to build even more efficient light bulbs in the future. Currently in 2022, no light sources with energy class A exist for the time being.
The new energy labels found on light bulbs not only feature the energy efficiency of the bulb, but also have a QR code that you can scan allowing access to more information about the bulb. During the transition phase, until the end of February 2023, you will find both the old and the new energy label advertised. It is worth noting that although the energy efficiency rating may have changed (for example A+ to F), the energy efficiency of the product has not changed, only the letter to which it is designated.
