Jim Lawrence Knowledge Base

Everything you need to know about bulbs

1. What bulb fitting do I require?

Common fitting types

Although there are hundreds of light fittings in existence, most homes only have a few different types the most common of which are shown below. The ‘B’ stands for bayonet and is most commonly used in the UK due to the British Empire, while the ‘E’ stands for Edison Screw - as in Thomas Edison - and is dominant in the USA and Europe.

The ‘cap’ or ‘base’ provides an electrical connection to the light and ensures the bulb is held in the correct position. It is essential to know the cap type to identify the right bulb for you. As a rule, the larger the cap the more wattage and heat it can take and therefore the brighter the bulb.

If you are replacing a bulb, it is a good idea to take it with you, so you know you have the right one. If not, you can use the images below, that show the most common bulb fittings in the UK, as a guide.

Small bayonet fitting
Standard bayonet fitting

Small Bayonet fitting (SBC, B15)

Generally used with smaller, lower wattage bulbs. Most are around 5 watts or equivalent to a 40 watt traditional (incandescent) bulb. There is not much difference between bayonet and screw fittings other than bayonets have the advantage of not working loose.

The vast majority of Jim Lawrence lights will take either a small or standard bayonet bulb. In many cases we can adapt the light fittings to take a screw bulb, but you will need to call us to specify this. Each light will have the bulb information on its product page.

Many of our wall lights are designed to take a small bayonet bulb as, aesthetically, this allows us to use a narrow candle tube which adds to the elegance of the design. Our Candle Shades have a candle clip fitting which can only be used with a Candle Bulb.

We supply three types of SBC bulbs: The Clear Candle LED Bulb which has a slightly elongated shape and is the recommended bulb for all wall lights that have fabric shades. Our SBC Golf LED Ball bulb which has a small round bulb, the 15 watt Pigmy bulb is a small, incandescent bulb that is supplied with our Masthead Light.

Dimmable – all our small bayonet LED bulbs are dimmable if used with a dimmer switch and have a warm white light.

Standard Bayonet fitting (BC, B22)

Also known as BS or B22 – has a larger twist and push fitting.
Width 22mm

Generally used with larger lights as they are designed to take a higher wattage and therefore produce brighter light than the small bayonet bulbs.  Our standard bulb is a Classic GLS LED that has a wattage equivalent to a 60 watt traditional (incandescent bulb).

We supply five different styles of BC bulbs, all LEDs:
  • Our Classic GLS LED  is the standard ‘pear’ shape
  • The Golf Ball LED which is a small, round shape
  • Our Squirrel Cage LED is a large, teardrop shaped alternative to the classic.
  • We stock a tubular shaped Tube LED for narrow cylindrical light fittings
  • The Globe LED is an oversized bulb that is often used on its own as well as in our larger light fittings.

Dimmable – all our standard bayonet LED bulbs are dimmable if used with a dimmer switch and produce a warm white light.
Small Edison screw fitting

Small Edison Screw fitting

Also known as ES or E14 – it has a small screw in fitting
 Width 14mm

Generally designed for lower wattage lights than larger screw bulbs and most commonly used in Europe and the USA. Most are around 5 watts or equivalent to a 40 watt traditional (incandescent) bulb.
We supply one ES screw bulb – our ES LED Clear Candle Bulb which has a slightly elongated shape and can be used as an alternative to the small bayonet bulb for our wall lights.

Please call us should you need your light fitted to take a screw bulb.

Dimmable – our Small Edison Screw LED bulb is dimmable if used with a dimmer switch and produces a warm white light.

Large Edison Screw fitting 

Also known as ES or E27 – similar to the Small Edison Screw but with a larger base
 Width 27mm

Generally used for larger lights needing a higher wattage as the larger the cap the more wattage and heat the lamp can withstand. Most commonly used in Europe and the USA, they tend to be around 7-10 watts or equivalent to a 60 watt traditional (incandescent) bulb.

We stock two E27 bulbs - our E27 LED Globe bulb is a beautiful oversized bulb that looks fantastic when paired with our larger glass lampshades such as the Lansdown, or it can be used on its own for an up-to-date industrial look. We also supply an E27 LED Reflector bulb that is a great choice to create bright directional lighting as its beam is channelled downwards by its reflective sides.
Large Edison Screw fitting
GU10 divider

What is a GU10 bulb?

Also known as a spotlight or PAR16 bulb – has two pins with small feet on the end that you push and twist into place similarly to a bayonet bulb.
The GU10 is the most common type of spotlight bulb found in most homes today. Often used in places where a bright, directional light is needed, such as kitchens and workspaces. It has the classic spotlight shape, with a narrow base that widens into a flat or slightly rounded aperture. Halogen GU10 bulbs are commonly made from plastic, not to be confused with an MR16 bulb that looks identical except for the much smaller, needle-like pins that will not fit a GU10 lamp.

We stock an LED GU10 that has the equivalent wattage to a 50watt traditional bulb.

It is dimmable if used with a dimmer switch and produces a warm white light.

What is a G9 bulb?

Miniature bulbs with two small looped pins protruding from the base. 
 Width 9mm

Traditionally these were mains voltage halogen capsule bulbs that were used in integrated fittings and appliances such as cooker hoods and kitchen cabinet lights. Now they’ve largely been replaced by LED versions which are longer lasting and more energy efficient.
As they are retrofit to existing fixtures, it is easy to replace your old bulbs. They simply slot into their fitting, but as they are often contained within integrated lamps, you may need to take the fitting apart to access the bulb. If you're not sure how to do this, or need help installing low voltage lighting, we advise consulting a qualified electrician.

We stock two G9 LEDs: G9 LED bulb that comes supplied with our Clipper and Derby wall lights and a G9 LED Capsule Bulb (Resin) that is supplied with our Malvern, Saunton and Clipper bathroom lights.
GU10 fitting
G9 fitting
Bulb types heading

2. What type of bulb do I need?

Common types of bulbs

Common bulb types

The bulb’s shape is not just about how pretty it looks but more importantly, about how it throws its light. Most household lights will require bulbs that direct the light everywhere (omnidirectional) but there are some that are designed to give a focussed light such as reflector bulbs, or Gu10 spot bulbs that often used in recessed ceiling lighting.

The three most common bulbs available on the High Street and all good DIY centres are energy saving types - CFLs, LEDs and Halogen bulbs. CFL stands for Compact Fluorescent Lamp and are typically found in fluorescent strip lighting and the old fashioned energy saving bulbs that used to take an age to warm up to full strength. They typically use 60-80% less energy than a traditional incandescent bulb.

Thankfully, technology has improved immeasurably since then and CFLs have largely been replaced by LEDs - Light Emitting Diodes. Although a little more expensive than other bulbs, LEDs are vastly superior in terms of cost efficiency as they as use an astonishing 90% less energy than traditional bulbs, and they last for years. They also light to full strength immediately and are available in many shapes and sizes and with heritage style filaments that make them better looking alternative to a CFL.

Lastly, halogen bulbs are readily available everywhere. These are closest in colour to traditional bulbs and use 20-30% less energy, but, like incandescent bulbs, don't tend to last long and more significantly, they give off a tremendous amount of heat which can burn fabric lampshades and for this reason we strongly recommend avoiding Halogen bulbs.


LED- Light Emitting Diodes

LEDs have been in common use for over half a century, mainly in electronic equipment, where they’re used as signals and indicators (standby lights, for example) but is only in recent years that they have been widely available for use in the home. They are now hailed as the future of home lighting as they are an energy efficient, longer lasting replacement for the old traditional incandescent light bulbs.

LEDs light to full strength straight away, emit the same brightness as traditional bulbs and only use a fraction of the power – around 90% less than traditional light bulbs. They therefore last 10-20 times longer and, unlike energy saving CFLs, can be recycled.

According to studies by Which magazine:
LEDs have an annual running cost of £1.71
CFLs annual running cost of £2.04
Halogens annual running cost of £8.42

LED bulb
When shopping for LED bulbs, remember the wattage doesn’t denote how bright a bulb. A 5W LED bulb is as bright as a 50W incandescent bulb. The lumens (lm) rating of a light bulb is the best indicator of its brightness.

LED bulbs differ from traditional incandescent bulbs in the way they produce light. While old-fashioned incandescent light bulbs passed electricity through a thin wire filament, LEDs produce light through the use of a semi-conductor that emits light energy when an electrical current is passed through it.

Early LEDs were limited by high prices and relatively low light output, but technology has developed rapidly in recent years and you can now get bright, efficient LED bulbs that replace 100W old-style bulbs and look just like a traditional bulb. What's more, prices are getting lower all the time. While some of the brightest bulbs cost around £20, most now cost less than £10 and the energy savings they will provide in your home make them well worth considering.


  • The most energy efficient type of bulb
  • Ultra-long lasting – around 25,000 hrs
  • Light to full strength immediately
  • Not hot so safe to use with fabric shades
  • Work well outside and in low temperatures
  • Available in all shapes and sizes and some styled with traditional looking filaments


  • Some LEDs can produce a cooler bluish light.
  • Most are dimmable but you may need a dimmer switch that recognises low electrical loads

Compact Fluorescent Lamp

Until recently, CFL light bulbs were the most common type of energy-saving bulb on the market as they’d long been used in strip lighting. Old-style incandescent bulbs had a filament inside that was heated until it glowed, which meant they used up energy to generate heat. CFL bulbs don't have a filament; instead they use an electric current to excite gases within the bulb that then cause a phosphorous coating on the inside of the bulb to glow, producing light. This method means less energy is lost to heat and the bulb uses less energy.

CFLs often come in stick and spiral shapes although some are now disguised as traditionally shaped bulbs. You can buy CFL light bulbs from many high-street shops and they typically cost between £2 and £15.


  • Cheap to buy
  • 60-80% more efficient than traditional bulb
  • Long lasting (average 10,000 hrs)


  • Take a while to warm up to full strength
  • Many are not dimmable
  • Some are not suitable for outside use or work poorly in cold conditions
  • They are not attractive to look at
CFL bulb
Halogen bulb

Halogen Bulbs

Halogen light bulbs are the closest you can get to old-style incandescent bulbs in terms of light quality. They score in the high 90s on the CRI scale (Colour Rendering Index) which is a measure of how well a light source accurately reveals various colours. CFLs and LEDs can’t match this but are still above acceptable levels.

Halogen bulbs have a filament enclosed in halogen gas, so they burn hotter than an incandescent bulb but still use less energy -  although they are not as efficient as CFLs or LED bulbs. They are commonly used in spotlight bulbs and come in a variety of classic bulb shapes.

We do not recommend using halogen bulbs with our lights as they produce a lot of heat which may scorch the shades, particularly smaller candle shades.


Closest replacement for incandescent bulb, similar light and wattages
Cheap to buy
Light to full strength immediately
Are dimmable
Available in all shapes and sizes


Very hot – might scorch fabric lampshades
Do not last as long as LED or CFL as the filaments blow

Bulb brightness heading

3. How bright do I want my bulb?

Lumens chart

What is Lumens?

Lumens is a measure of how much light you are getting from a bulb. More lumens means it’s a brighter light; fewer lumens means it’s a dimmer light.

Watts vs Lumens
When shopping for bulbs, remember the wattage doesn’t denote brightness. In the past, when we filled our homes with incandescent bulbs, brightness was measured in watts - which is actually a measure of power i.e. how much energy the light consumes to produce its light.

Since the introduction of energy-saving bulbs, it 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.
Kelvin divider

4. Do I want warm or cold light?

Kelvin chart

What is Kelvin?

There is nothing worse than getting home and finding your new bulb casts a cold, blue light instead of a warm white one. The colour of light is measured on the Kelvin scale, which is actually a measure of temperature. Named after the Belfast born scientist that invented it, the Kelvin Scale relates to the degree of temperature a colour measures on it. The lower the light temperature rates on the Kelvin scale, the ‘warmer’ and more red the light appears to the eye. The higher it is on the Kelvin scale, the ‘cooler’ and more blue the light appears to us. This is why light bulb manufacturers often refer to 'colour temperature' on the packaging.

Most people like the warm white light given out by the old incandescent bulb, which is 2,700 on the Kelvin scale. A very orange light has a low number of kelvins, e.g. a candle flame is about 1,500k. Daylight is much colder so is around 5,000k. 
CRI scale heading

5. How true do I need my bulb to reflect colour?

CRI colour rendering index

What is CRI or Colour Rendering Index?

The Colour Rendering Index (CRI) is the measurement of how colours looks to the human eye under a light source when compared with sunlight. The index is measured from 0-100 with natural sunlight having a perfect score of 100. The higher the CRI the better the colour rendering ability. Any light scoring 80-100 means that the colours illuminated by it appear the same, or nearly the same as they would under natural sunlight. The rating is used by the lighting industry to help discern the colour accuracy of lights. Lights with a CRI of 80 or more are considered to be more than acceptable for most applications.

It should be pointed out that CRI has nothing to do with the colour temperature of a light (warm or cold light) as measured by the Kelvin Scale discussed above. It is possible for lights with the same degree of Kelvin to have completely different CRI ratings, e.g. an incandescent bulb of 2700K (warm) can have a CRI of 100 (equivalent to daylight) while a fluorescent light source at 5000k (daylight) can have a CRI of 75.

The reason for the differences is to do with the way a light source distributes colours in the visible colour spectrum which are made up of different wavelengths. Daylight distributes these wavelengths more widely than most electric light sources, meaning the human eye can discern between subtle shade differences better in daylight than in electric light.

Generally, all incandescent and halogen bulbs have a CRI close to 100 meaning they are excellent at rendering colour. By comparison the CRI of LED and CFL bulbs can vary a lot so always check the packaging for a CRI of 80 or more if you want a true reflection of colour.