Lighthouse scores may not accurately reflect how users experience a website. The score can be impacted by testing conditions like internet speed and Chrome extensions. PageSpeed Insights shows real-world data from users alongside Lighthouse lab data, giving a fuller picture of performance. Lighthouse is best used to compare changes during development rather than measure actual user experience, and results should be taken with some skepticism as tricks can influence scores.

1. You’re Probably Using
Lighthouse Wrong

2. Filip Rakowski
Co-founder & Chief DX Officer
Technology Council Member
I’m on Twitter!
@filrakowski

3. Accelerate and
simplify the
development of
storefronts!
/vuestorefront

4. -
@filrakowski
fn(⚡) = 💰

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@filrakowski

6. -
@filrakowski
_2017_

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@filrakowski

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@filrakowski

9. -
@filrakowski
We are here

10. -
@filrakowski
2017: Mobile phones are becoming preferred way of consuming
the web. Colorized.

11. -
@filrakowski
15,3s
Average Loading Time on Mobile,
Google Research, 2017

12. -
@filrakowski
Google Lighthouse
April 2018 - Lighthouse lands in Chrome!

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@filrakowski

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@filrakowski

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@filrakowski
👍
👎

16. @filrakowski

17. @filrakowski

18. @filrakowski

19. @filrakowski

20. Good decision = DATA + CONTEXT

21. @filrakowski

22. @filrakowski

23. @filrakowski

24. @filrakowski

25. How Lighthouse works?

26. @filrakowski
googlechrome.github.io/lighthouse/scorecalc/

27. @filrakowski

28. It matters A LOT where
you run the audit

29. @filrakowski
Chrome Devtools
● Results affected by your
internet speed and CPU
(even with throttling)
● Chrome extensions can
significantly impact the
result (use incognito!)
● Generally not very reliable

30. @filrakowski
Page Speed Insights
● Runs at closest Google Data
Center (if it has bandwidth)
● Shows both field data from
real users (top) and lab data
from Lighthouse

31. @filrakowski
Pagespeed Insights

32. @filrakowski
Pagespeed Insights
Real-world data
(your users) collected from
CrUX
Results of LH audit run on
Google Data Center
IMPACTS SEO!

33. Be suspicious about
Lighthouse score - it’s
easy to trick it

34. @filrakowski

35. @filrakowski

36. When and how does it
make sense to use
Lighthouse?

37. Good performance is a tradeoff
@filrakowski

38. Use Lighthouse to get a
perception of how new release
will affect your performance
@filrakowski

39. Don’t use Lighthouse to
measure how your users
experience your website
@filrakowski

40. @filrakowski

41. @filrakowski

42. Lighthouse and real-world
data can be very different

43. @filrakowski

44. Thank you!
vuestorefront.io/developer-newsletter
Daily(ish) tips about webperf, vue, Nuxt and whatever I find interesting.
@filrakowski