Lighthouse Analysis Uses Medium-end Smartphone on 3G Connection
Lighthouse analysis uses an average smartphone on a 3G connection to measure speed. This might account for discrepancies between Lighthouse and independent tests which might be carried out over a much faster Wi-Fi connection.
Server Location Shouldn’t Impact Google’s Page Speed Measurement
The geographic location of a web server shouldn’t impact Google’s measurement of page speed. They have labs data to artificially measure the speed a page would take, and field data to measure the speed of pages for real users.
Google Speed Tool Scores Don’t Map One-to-one with How Speed is Used for Rankings
The scores shown in Google’s page speed tools such as PageSpeed Insights don’t map one-to-one with how sites will be ranked in search in relation to their speed.
Lab Data & Field Data Differ in New PSI Tool as User Devices Differ From Google Default
The lab data can differ from the field data in the new PageSpeed Insights tool because users sometimes have different devices than the default device that Google would use for testing.
Web.dev is Built on the Lighthouse Infrastructure in the Back-end
Google’s web.dev tool is built on Lighthouse in the back-end to maintain consistency with other tools.
Pages With Long Download Times Reduce Googlebot’s Crawl Budget
If a page takes a long time to download then this will use up crawl budget for Googlebot, meaning it will have less time to crawl other pages on your site. Look at the ‘time spent downloading a page’ report in GSC to spot these issues.
Combine Separate CSS, JS & Tracking URLs to Increase Googlebot Requests to Your Server
To improve site speed and allow Googlebot to send requests to your server more frequently, reduce the number of external URLs that need to be loaded. For example, combine CSS files into one URL, or as few URLs as possible.
New PageSpeed Insights Tool Uses Lighthouse Data & Runs Lighthouse Audits
The new PageSpeed Insights tool runs Lighthouse audits for you using data from across different devices.
Inconsistency in PSI Alerts Suggests Being on the Edge of Google’s Speed Requirements
The PageSpeed Insights team try to maintain stable tests for websites, so if a site has fluctuations between getting alerts and passing the tests, this suggests the site is right on the edge of Google’s speed requirements.