When importing photos into your Lightroom, you have 4 choices for your previews:

  1. Minimal
  2. Embedded and Sidecar
  3. Standard
  4. 1:1

Why the choices? Lightroom generates the previews on the fly as needed, whenever you zoom in the photo at 100% or in the Develop module. The problem is speed versus convenience. No matter what, you will have to pay the piper, either on the front-end or on the back-end, but you will pay the piper. In this case, it’s building the previews.

Previews take a lot of CPU power to build and a lot of disk space to store.

Minimal Preview

Selecting the Minimal Preview setting, for the import, directs Lightroom to only build a thumbnail for the grid view. It’s the thumbnail used in the filmstrip. If your grid is larger, then Lightroom will build the standard preview and the 1:1 preview as needed when needed. This is the fastest import.

Embedded and Sidecar Preview

Selecting the Embedded and Sidecar setting, for the import, directs Lightroom to grab the embedded JPEG from the photo. All the RAW photos created by every camera include a small JPEG. That’s the JPEG that you see when you are reviewing the photo on the LCD at the back of your camera.

Lightroom will use that image for the Grid view. If you zoom in and/or switch to the Develop module, Lightroom will build the full, 1:1 preview. That’s when you wait and see the message “Loading…” for 4, 5, 6 or 10 seconds depending on the speed of your CPU.

Standard Preview

Selecting the Standard Preview setting, for the import, directs Lightroom to build a higher quality preview. It’s a higher quality than the thumbnail or the JPEG from the embedded. It will be used up to the FIT size (assuming a “standard” monitor). But, if you zoom in and/or switch to the Develop module, Lightroom will build the full, 1:1 preview. That’s when you wait and see the message “Loading…” for 4, 5, 6 or 10 seconds depending on the speed of your CPU.

1:1 Preview

Lightroom uses the full preview that Lightroom when you select 1:1 or switch to the Develop module. Since they take so much disk space, and Lightroom was originally written when the standard hard disk was a “small” 120Gb. You can set the catalog to delete the 1:1 previews 30 days after the last use by going to the Catalog SettingsFile Handling tab.

  • What do I use? 1:1 previews and keep them forever.
  • Why? I don’t have the patience of waiting and seeing the message “Loading…” for 5 seconds when I switch from one photo to the other.

The previews are not stored in the catalog. They are just thousands upon thousands of files in the directory catalog name with Previews.lrdata.