Light Bulb Guide

Pagazzi Lighting: Light Bulb Guide


Which light bulbs generate the most heat? Which bulbs last the longest? Which bulbs are energy efficient? What bulb cap do I need?

If you often find yourself asking these kinds of question, then this handy guide from Pagazzi should clear up most of the common confusions we've heard our customers feel when shopping for light bulbs. This short guide will equip you with all the knowledge you need to shop for bulbs with ease and confidence, sure of what you're getting.

If you still have questions, or even if you'd just like a little peace of mind, don't hesitate to get in touch via telephone or email and one of our friendly and knowledgeable staff will be more than happy to help.

Bulb Caps

In the UK there are three primary types of bulb caps for domestic fittings. We'll walk you through them one by one explaining the key information you need to be aware of when selecting your cap.

Bayonet Bulbs

Bayonet light bulbs are primarily found on the UK lighting market and are recognisable by their 'push/pull' fitting function, whereby small rods on the base of the cap slide into corresponding grooves in the fitting and are twisted into place. The most common product codes for Bayonet Bulbs are BC or B22d, with these caps measuring 22mm in diameter. These bulbs also come in a smaller size known as SBC or B15d, but these are slightly less common.

It is always best to take a note of the bulb code from any new light fittings your purchase to ensure you have a copy for your reference each time you have to replace the bulb. All bulbs are marked with the relevant cap code.

Edison Screw Bulbs

Named after the lighting pioneer Thomas Edison, this is the most popular type of light bulb used in homes across the UK. With an easy screw-in design, the Edison Screw bulb comes in a variety of sizes, the most common of which are the ES/E27 or SES/E14. Similarly to the Bayonet Bulbs, the numbers in the Edison codes refer to the diameter of the cap. These bulbs can also be found in decorative shapes such as the iconic candle-flame design often used in  chandeliers.

Halogen Bulbs

Halogen bulbs are primarily available in two forms. The smaller bulbs are generally characterised by their small rods which are simply pushed into the light fitting. Their larger counterparts feature prongs which are twisted into position in a similar method to the Bayonet bulbs. The most popular bulb codes for the smaller halogens are G4 and G9 with the number referring to the distance (mms) between the prongs. The most common larger bulb codes are GU10 and are primarily found as spotlights in track lighting or sunken ceiling spotlighting. The EU have recently passed legislation to phase Halogen bulbs out of the UK to be replaced with LEDs. We’ll cover LED bulbs and the changes in legislation in depth, further down this guide.

As well as the cap of the bulb needing to be right, it's also important that you get the right shape for your fitting as well. You don't want to come home with a bulb that technically fits, but that sticks out of the fitting ruining the overall look. Again the shape of the bulb will be clearly marked on the packaging of the fitting, so take a note and you can match it up when shopping for a replacement bulb. Where possible it's always best practice to take the old bulb with you when shopping for a new one, just to be absolutely sure you're picking the right one.

Watts vs Lumens

When we're talking watts and lumens, what we're really talking about is brightness. Back before the ban of incandescent light bulbs, the brightness of a light was measured in watts, which are actually a measure of how much power it takes to illuminate the light bulb. Nowadays energy saving bulbs take much less energy to generate the same amount of light. This means that using lumens as the standard of measurement gives a much better indicator of what you're paying for.

In simple terms: the higher the number of lumens, the brighter the light will shine.

Kelvin Scale

Of course bulbs have long since been available in a vibrant array of exciting colours (think back to that creepy Halloween party you went to where everyone was bathing in blood red lighting!), but the colour of bulbs can actually vary much more subtly, and can really affect the mood and feeling of your home. In order to properly pin down what colour of light a bulb will emit, it's best to understand what your preference is on the Kelvin Scale.

The Kelvin Scale is actually a measure of light temperature which is often how it will be referred to on the packaging. Light temperature can range from warm - giving off a warm amber glow creating a cosy feel (perfect for your living room) - to stark white which may be more suitable in an environment where perfect visibility is of key importance, such as a hospital or an industrial kitchen.

Colour Rendering Index (CRI)

Each bulb is also given what's known as a CRI value. This stands for Colour Rendering Index and refers to a light bulbs ability to correctly represent colours. You want to ensure that you choose a bulb that accurately shows the colour of the wallpaper you spent hours debating over, rather than have a bulb cast it into a slightly altered shade you didn't pick out! The traditional incandescent light bulbs scored in the high 90s for their CRI value which is considered near perfect meaning that your lettuce will look green and your tomatoes will look red. It is not advised to go below 80 for your CRI score when picking out light bulbs or you may find yourself sitting in a room full of colours that look a little bit off!

LED (Light Emitting Diode)

Although not the most glamorous topic, when it comes to light bulb technology a little knowledge really can go a long way towards helping you shop for bulbs with confidence and get the best out of your light fittings.

You’ve probably heard chatter about LED bulbs and how their better value for money and better for the environment, but never really taken too much notice. Don’t worry, you’re not alone! But with new EU legislation coming into effect from September 1st 2018 which will start to phase Halogen bulbs out of the UK, it really is time to make the leap to LED.


LED bulbs are much cooler than traditional light bulbs.

In order to create light, we need to use energy.  An unavoidable by-product of creating light is that some of the energy ends up being wasted as heat, which isn’t what we want from a bulb. LED bulbs convert up to 85% of all energy used into light, which means only 15% of the electricity you’re paying for is wasted as heat. In comparison Halogen bulbs waste 65% of the energy as heat, which is a substantial amount of your electricity bill to represent wasted energy. Switching to LED is not only better for the environment but easier on the pocket, too. Spending a little more upfront on LED bulbs will lead to savings on your energy bill over the course of the bulbs life, savings which far outweigh the initial difference in price between the bulbs.

Energy Efficiency:

LED bulbs are also advancing all the time, meaning that although their wattage (the amount of energy required to power the bulb) may be coming down, their lumens (the brightness of light the bulb produces) is rising all the time. For instance, a 5 watt LED bulb generates just as much light as a 50-watt halogen bulb. This means that LED consumers are spending less on energy, but getting brighter bulbs as time goes on. Don’t let yourself be put off by LED’s low wattage and worry you might end up sitting in the dark! Remember that wattage is not about how bright the bulb is, it’s only a representation of how much energy the bulb will need to run.

Bulb Life Cycle:

The life expectancy of LED bulbs is substantially higher than their Halogen counterparts. LED bulbs can last as long as 25 years (or 25,000 light hours) which is 10 times longer than most Halogens. That means buying and changing lightbulbs a whole lot less often than in the past if you make the switch to LED.