Google Lighthouse Performance

The Google Lighthouse performance score is a metric that measures the speed and performance of a website. It’s an overall score that ranges from 0 to 100 and is generated based on a number of different performance metrics, such as the time it takes for a website to load, the time it takes for a website to become interactive, the size of the resources used by the website, and other factors that impact the user experience.

A high performance score in Google Lighthouse indicates that a website is fast and responsive, which can lead to a better user experience and improved search engine rankings. On the other hand, a low performance score can indicate that a website is slow and unresponsive, and can negatively impact the user experience.

Mobile Performance
Desktop Performance

Core Web Vitals

Core Web Vitals are a set of specific factors that Google considers important in a webpage’s overall user experience. Core Web Vitals are made up of three specific page speed and user interaction measurements: Largest Contentful PaintFirst Input Delay, and Cumulative Layout Shift.

Largest Contentful Paint11.9 s2.9 s< 2.5 s
First Input Delay410 ms80 ms< 100ms
Cumulative Layout Shift0.980.236 0.1

Tracking scripts

All the tracking scripts on the site generated ~52 KB of data

A tracking script is a code snippet designed to track the flow of visitors who visit a website. Media, advertising, and analytics organisations will provide a script to add to your website that sends data directly to their servers. This data can then be used to measure goals and conversions, analyse user behaviour, and influence advertising campaigns.

Consider how much of this data you actually need and use? How often do you review the analytics data, and does this inform genuine change? Are you actively running social media campaigns? Consider pausing or removing tracking scripts that aren’t being actively used. 1 52 KB 1 407 B


Optimise images

By optimising the following images, roughly 1 MB could be removed from the transfer size, about 41%. This would reduce the CO2 generated per page load from 0.78g grams to 0.46 grams.

Images should be optimised for the web for several reasons:

  1. Reduced file size: Optimizing images can result in a smaller file size, which can help to reduce the amount of data that needs to be downloaded. This can lead to faster page load times and improved performance.
  2. Improved user experience: Optimising images can help to improve the overall user experience, as pages with optimised images load faster and are more responsive.
  3. Lower emissions: Optimising images can help to reduce the emissions associated with data transfer, as less data needs to be transmitted over the network.
  4. Better accessibility: Optimising images can make them more accessible to users with slower connections or limited data plans.
ZWW_banner_V3.jpg 272 KB 8% 241 KB
ZWW_news_banner_V3.jpg 194 KB 6% 166 KB
SR-News_Carousel.jpg 188 KB 5% 161 KB
Our-Latest-Results-_Widget_.jpg 178 KB 5% 151 KB
BRL338_V1_Cover_SR.jpg 174 KB 5% 152 KB
Generic_2.png 172 KB 5% 157 KB
331-V2_1-DJSI-Number-1-News-Widget-Image.jpg 172 KB 5% 147 KB
BRL353_V1_2_Net-Zero-News_Slider.jpg 93 KB 3% 45 KB
Kendra.jpg 84 KB 2% 59 KB
2022-Full-Year-Results-_News-slider_.jpg 54 KB 2% 26 KB
Download-the-2022-Corp-Gov-_Widget_.jpg 53 KB 2% 37 KB
Download-the-2022-Annual-Report-_Widget_.jpg 50 KB 1% 35 KB
Growth_2.jpg 47 KB 1% 33 KB
asset_1.jpeg 33 KB 1% 28 KB

Replace icon font files

Font icons can have a negative impact on performance and emissions because they can increase the size of the page and the amount of data that needs to be downloaded. Some specific reasons why font icons can be bad for performance and emissions include:

  1. Increased file size: Font icons are typically included as part of a web font, which can be a large file that needs to be downloaded. This can increase the overall size of the page, leading to slower load times and higher emissions.
  2. Inefficient rendering: Web fonts are sometimes loaded and rendered inefficiently, which can result in slow performance and higher emissions.
  3. Unused icons: Font icons often include a large number of icons that may not be used on a particular page, increasing the file size and leading to inefficient use of resources.

While icon fonts are still widely used on the web, and they can be a useful tool for adding icons to a website. it is a dated practice when there are better options such as SVG icons, which can be more efficient and have a lower impact on performance and emissions.

fontawesome-webfont.woff276 KB

Remove third party font files

Font files should be loaded from the same hosting as the website because

  1. Increased loading time: Third-party sub-resources, such as scripts, fonts, or images, need to be downloaded from a separate server before they can be displayed on the website. This can increase the overall loading time of the page, leading to a slower user experience.
  2. Dependence on external servers: The loading of third-party subresources is dependent on the availability and performance of the external servers that host them. If these servers are slow or unavailable, it can result in slow page loading times or even errors.
  3. Increased risk of security threats: Third-party subresources can introduce security risks to a website, as they can contain malicious code or be used to track user activity.

First Contentful Paint

First Contentful Paint (FCP) is a performance metric that measures the time it takes for the first piece of content to be rendered on the screen when a user navigates to a web page. This content can be any visual element on the page, such as text, images, or a background color.

FCP is important because it directly affects the perceived speed of a website, and can impact user engagement and conversion rates. A faster FCP can lead to a better user experience and improved performance.

Here are a few ways you can optimise your FCP:

  1. Optimise images: Large, unoptimised images can slow down a page’s FCP. You can optimise images by compressing them, reducing their dimensions, and choosing the right format for each image.
  2. Minimise HTTP requests: Each resource requested by a web page, such as images, scripts, and stylesheets, requires a separate HTTP request. Minimising the number of HTTP requests can help to reduce the time it takes for a page to render.
  3. Prioritize critical content: Prioritizing critical content, such as above-the-fold content, can help to ensure that users see something on the screen quickly, even if the rest of the page is still loading.
  4. Reduce server response time: A slow server response time can significantly impact FCP. Optimizing server-side code and server settings can help to reduce response times and improve FCP.
  5. Use a performance monitoring tool: There are many tools available that can help you monitor your website’s performance, including FCP. These tools can help you identify performance issues and track your progress as you implement optimizations.
Timing4.7 s1.1 s

Largest Contentful Paint

Timing11.9 s2.9 s

Total Blocking Time

Timing1,490 ms40 ms

Cumulative Layout Shift


Speed Index

Timing15.4 s4.5 s

Time to Interactive

Timing13.4 s2.6 s

Max Potential First Input Delay

Timing410 ms80 ms

First Meaningful Paint

Timing4.8 s1.1 s

Eliminate render-blocking resources

InsightPotential savings of 1,340 msPotential savings of 430 ms

Properly size images

InsightPotential savings of 258 KiBPotential savings of 477 KiB

Reduce unused CSS

InsightPotential savings of 39 KiBPotential savings of 83 KiB

Reduce unused JavaScript

InsightPotential savings of 886 KiBPotential savings of 895 KiB

Efficiently encode images

InsightPotential savings of 876 KiBPotential savings of 876 KiB

Serve images in next-gen formats

InsightPotential savings of 1,437 KiBPotential savings of 1,437 KiB

Reduce initial server response time

InsightRoot document took 4,730 msRoot document took 3,580 ms

Preload Largest Contentful Paint image


Avoid enormous network payloads

InsightTotal size was 3,579 KiBTotal size was 3,501 KiB

Serve static assets with an efficient cache policy

Insight25 resources found24 resources found

Avoid an excessive DOM size

Insight1,341 elements1,341 elements

JavaScript execution time

Timing4.8 s0.9 s

Minimizes main-thread work

Timing9.2 s1.8 s

Ensure text remains visible during webfont load


Minimize third-party usage

InsightThird-party code blocked the main thread for 1,040 msThird-party code blocked the main thread for 20 ms

Largest Contentful Paint image was not lazily loaded


Does not use passive listeners to improve scrolling performance


Avoid document.write()


Image elements do not have explicit width and height