Why the audit is important
Perceptual Speed Index is a page load performance metric that shows you how quickly the contents of a page are visibly populated. The lower the score, the better.
How to pass the audit
To lower your Speed Index score, you need to optimize your page to visually load faster. Two good starting places are:
How the audit is implemented
This section explains how this audit is implemented, so that you can understand how the audit's score is calculated.
Lighthouse uses a node module called Speedline to generate the Speed Index score.
For more information on the algorithms and methodologies behind Speed Index, see Speed Index.
The target score is computed by a cumulative distribution function of a log-normal distribution. Check out the comments in the source of the audit if you need to know more.