Lighthouse scores – What are they and why are they important?

What is a lighthouse score?

Every webpage that is crawled by a search engine is evaluated with a score from 5 categories: Performance, Accessibility, Best Practices, SEO and PWA. This is given a score between 0 – 100. The better your lighthouse score is will affect how high up your webpage will appear on a search engine.

Each of these categories are judged on the following:

  • Performance is judged on how quick it takes your webpage to load.
  • Accessibility is judged by how accessible your website is. Especially for users who might require technology such as a screen reader or have difficulty with colors.
  • Best Practices are judged by factors which will usually only be apparent to developers. This will be on code health, for example, Using deprecated Libraries/APIs, Asking for permission if you want the users locations and making sure that it is a secure connection of HTTPS.
  • SEO (Search Engine Optimisation) is judged by making sure the page is optimised for search engine results. This is a large area of website design but some simple examples could be Header names and using keywords, Making sure images have descriptive names so a search engine can label them.
  • PWA (Progressive Web Apps) does not receive a score, it is either there or not. This is still a rather early technology but makes websites run faster on repeated views.

With a high score, your site meets the best practices and SEO standards outlined by Google in terms of performance and accessibility. Lighthouse is an important tool because it can identify common problems that affect the quality of your websites and propose solutions for them. 

How does it work?

When a Google Lighthouse audit is performed, the tool loads the target website several times and collects metrics about the structure, tags and performance of the site. The audit provides a performance report in several categories, including metrics, opportunities and diagnoses. For this reason, it is important that you perform an audit on your site. It may expose certain performance weaknesses on your site that affect the user experience and give you the insight you need to reverse them and optimize things.

Why is it important?

A high Lighthouse score is important for Google. Google will change the ranking of the targeted website depending on this score. For a business it is crucial to get your webpage onto the first page of Search engines and within the first five results. Users of search engines very rarely go beyond the first page. If your business is trying to sell or promote a product, you want to have as many viewers as possible. 

Having a high accessibility score is vital. You don’t want to block off any of your users from being unable to consume your content. The more users who can access your site, the more potential business you could receive.

A high Lighthouse score also means that you have a well performing website. The speed that a page loads at is extremely important as users do not want to sit around waiting for your webpage to load. The minimum page load time that is recommended is two seconds, this is what a user unconsciously expect. If your page takes longer than this your user will slowly get frustrated at your website and may end up leaving.

Google concludes that slow websites are a problem of usability and SEO, because we know that users don’t like waiting for web pages to load. The speed of the sites feed into Google’s search results. Google knows that it can be detrimental to the user experience if people switch to slow-loading websites, which is why it attaches great importance to page speed in determining its rankings.

The importance of website loading time

Website loading time depends on a number of factors, such as the host server, the bandwidth that passes through the website, the design of the page elements, the browser and the device type. Google’s recommended load time for websites on desktop and mobile devices should be less than 3 seconds. Excessive delays in mobile page loading times occur when websites are not optimised and designed to provide powerful interfaces for mobile devices. In fact, 46% of people on mobile say they do not want to wait for a page to load while browsing the web, and 73% of mobile users come across websites that take too long to load. Just as web pages are the same, web pages have different loading times due to developer decisions, content richness, page structure and functionality, and the number of elements on the page. 

Every second of delay in loading the page causes frustrated visitors to leave a slow website. This results in a 7 percent loss of conversion rate, 11 percent fewer page views, and a 16 percent drop in customer satisfaction. Content relevance is paramount, and if you want to get onto the search engines results page, loading times of websites are confirmed by Google, so it’s important to speed up your pages to have a better chance of SEO success.

You may be wondering if loading a few milliseconds onto your website can have a big impact on the customer experience and business growth. Page loading times are a hot topic of website improvement, which not only increases demand from mobile visitors, but also has the potential to lead to customer losses. The interval known as the “gap of death” between the expected page loading time of 2 seconds and the average website load time of 5 seconds has been widened and shortened due to neglect of website optimisation tactics and business decisions. 

How hard is it to improve your lighthouse score?

Most website issues are clearly pointed out by the performed audit. The most common that I have come across are:

  • Have images at multiple sizes so the webpage only loads the minimum size.
  • Removing unused
  • Making a background and foreground have a higher contrast ratio
  • Links not having descriptions.

All of these are very simple and slight changes that can improve your website. When you do the audit you get suggestions like the following: 

The audit also adds the estimated savings which is how much time you could save by doing this. Since the maximum page load time should be 2 seconds, every millisecond counts.

We are a UK Digital services and software development company. We provide Lighthouse audits and improvements for your site. If you’d like to know more or need some further advice or support then you can get in touch with our team via email:



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