Understanding Lighthouse Performance Metrics - SEO Tips From Semalt

Lighthouse performance metrics is something you are likely to come across when discussing the technical aspects of SEO. You may be wondering what this test consists of or how to run the test on the performance of your website. You might also be here because you want to find out what Lighthouse is all about.

We use this performance metrics test in our attempt to make all the numbers that relate to your site green. Here is all you need to know concerning Lighthouse.

What is Lighthouse

Lightroom is an open-source auditing tool used to produce standardized scores in five key areas, namely:
  • Performance 
  • Progressive web app 
  • SEO 
  • Best practices 
  • Accessibility
For this article, the name "Lighthouse" will be used to refer to a series of tests, so do not get confused while reading. 

Lighthouse runs performance tests using lab data, which is also called emulated data. This is a site's performance data collected in a manmade environment with predefined devices and network settings. Performance data is important as it helps with the necessary information for debugging performance issues. The experience on the local machine in a controlled environment is designed to mimic the experience of real-life users. 

Updating to Lighthouse

On May 5, 2020, the Chromium project announced its set of three metrics with which the Google-backed open-source would be able to use in measuring performance. The metrics were called Web Vitals. They are part of Google's initiative, designed to provide collective guidance for SEO experts when searching for quality signals. 

These metrics are designed to measure web performances in a user-centric manner. In only two weeks from its initial launch, Lighthouse V6 launched its modified version with Web Core Vitals as the primary focus of this update. 

By July 2020, we saw Lighthouse v6's metric getting adopted to many of Google's products with the release of Chrome 84. Chrome DevTools Audit panel was also renamed Lighthouse. The Lighthouse metric was also referenced by PageSpeed Insights and Google Search Console. 

Today, Web Core Vitals makes up over half of the total Lighthouse weighted performance score. Generally speaking, pages begin to experience minimal impact, with approximately 83.32% of tests conducted showing a shift of ten points or less to V6. 

What you must know before running the Performance test using Lighthouse

Picking the Right Methodology

The methodology you choose to walk with matters. Lighthouse audits are set to analyze a page at a time. But the fact is that a single page score isn't the representation of the performance of your entire site, and just because your home page is quick to load doesn't mean your entire site loads as fast. 

The best way to get an overall estimate of how well a site performs is to test multiple pages types within your site. Here, we first identify the major site types, templates, and visitor conversion points (they refer to the sign-up, subscribe, and checkout pages). 

Before we proceed to the optimization stage of our analysis, we run Lighthouse on every of the randomly selected sample page and record the data collected. From this data, we can now create a to-do list based on the most pressing to least pressing improvements. To prevent the loss of any data, we save the JSON results and rely on the Lighthouse viewer whenever we require a piece of detailed result information. 

Getting the Backlog to Bite Back Using great ROI

Over the years, one thing we've learned for certain is that getting the resources needed for SEO action is not straightforward. Having an in-house SEO isn't exactly helpful as they are often destroyed by how difficult it is to get a backlogged ticket. From our experience, we know that the best way to grease the gears is by getting performance initiatives prioritized, which results in excellent numbers that back up the investment made to the SEO department.

The data that makes it to the end of the month account sheets will become the dollar signs that justifies and rewards our development efforts. Performing this test is important because while doing so, you are likely to have more than one area flagged, especially when it is the first time. That's okay. You can check out Lighthouse Scoring Calculator to see which changes will have the biggest bangs. 

How to Run a Lighthouse Test

This is the case of many paths leading to one river. However, there are certain paths that stand out to be easier or more prominent in use. Well, if you are hoping to integrate the SEO test into the realizes process, you probably should be brought up to speed on NPM. 

Do you have less than 5 minutes before you're asked to face the board? These one-on-one reports should give you the ammunition you need to convince them that your SEO is doing great. Whichever execution method you choose, mobile is excellent unless you have a special use-case for desktop. 

1. Chrome Devtools

We test each page individually using the Chrome DevTools Lighthouse panel. This report is vital as it emulates a user experience using the browser even while on incognito or with the browser cache disabled. 

Our special way of approaching this is to create a Chrome profile for testing but keep it local. That means no Sync enabled, no password saving, or association to any existing Google account. We also do not install extensions for the user. 

When you're set, here is how you test Lighthouse using DevTools 
  1. Run an incognito instance on Chrome.
  2. Go to the Network panel in DevTools and tick the box to disable the cache. You can do this with Ctrl + Shift + I on Windows and Linux or Command + Option + I on Mac.
  3. Go to the Lighthouse panel and click generate a report.
  4. Save the file once generated. 
What are the benefits of running Lighthouse from Devtools?

Like we mentioned earlier, there are many ways to run lighthouse analysis. What this also means is that each method has its pros and cons. 

The benefit of this method is that
  • You can test local builds and find out which pages are authentic.
  • The reports that are saved can be compared with the Lighthouse CI Diff tool. 
Cons of running Lighthouse from DevTools
  • You can only do one report at a time.
  • You will have to save each report manually.

2. When testing the same pages continually

Suppose you're fond of testing the same pages repeatedly, web. dev is the ideal pick. It's similar to using DevTools only that you wouldn't need to disable all those peaky extensions. This method is basically straight forward. All you need to do is:
  1. Visit web.dev/measure/
  2. Sign in with your Google account.
  3. Enter the URL of the page you would like to audit.
  4. Click run audit.
Pros of running Lighthouse from the web. dev 
  • It captures the nifty timeline of the page's results. 
  • Users have quick links on guides for improving issues. 
  • Reports can be compared using Lighthouse CI Diff Tool.
Cons of running Lighthouse from the web. dev
  • You can only conduct one analysis and have one report at a time.
  • You have to have a record of the URLs you've tracked over time to avoid redoing the same URL unintentionally.

The Node Command-Line for Lighthouse

When you're looking to test at scale, the Node Command-Line is the preferred approach. Here is a guide on what to do:
  • Install npm: for mc users, it would be wise to use homebrew so you can avoid silly dependency issues. 
  • Install the lighthouse Module by simply inputting this code: "npm install -g lighthouse."
  • You then run a single text using "lighthouse <url>."
  • Run tests on lists of usings by running the test programmatically. 
Pros of running Lighthouse from Node
  • You can run multiple reports at once.
  • You can program it to track changes over time automatically.
Cons of running Lighthouse from Node
  • You must have an idea of how to code.
  • Its setup requires time.


The complexities of Performance metrics are an indicator of the challenges every site faces. We rely on performance metrics as a proxy for user experience. It allows us to walk the path of a user and see what they see, experience what they experience in others to build more responsive sites. 

Some other tools like the test My site Tool and What does My Site Cost by Google can also come in handy. We use these tools to make the conversion and customer-focused arguments for the importance of performance in a site. 

Hopefully, once your project gains traction, we can explain what your Lighthouse's single metric performance means to your skilled and collaborative engineering team.

Interested in SEO? Check out our other articles on the Semalt blog

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