My first article on Lightroom was: Lightroom: Slow As Molasses Or Lightning Fast?.

I did some further testing with actual numbers: What’s Lightroom’s speed when browsing the same 100 photos of the same catalog with all these photos after having generated the 1:1 preview:

Mode Time % slower
Library @ fit setting 1 mn 42s 0%
Library @ fill setting 1 mn 45s 3%
Library @ 1:1 setting 3 mn 53s 129%
Develop @ fit setting 5 mn 11s 205%
Develop @ fill setting 5 mn 12s 206%
Develop @ 1:1 setting 6 mn 04s 257%

Conclusion:

  1. Browse the catalog in the library module.
  2. Generate the 1:1 previews during the import.

If I didn’t generate the 1:1 previews during the import, or would have deleted the 1:1 previews, browsing at the fill setting and/or the 1:1 preview setting would have been about 5 times slower.