Although it's rare, sometimes one or more of the following issues can occur, and if they do, you may need to delete your preview cache file:
- Your hard disk gets unexpectedly full.
- You get an error about your cache in Lightroom.
- You get artifacts—such as lines, dots, or unexpected colored areas—in your images.
The file that contains your thumbnail and preview data is called [Catalogname] Previews.lrdata, and is in the same folder as your catalog.
Your thumbnails, small previews, and 1:1 (full size) previews are kept in this Previews.lrdata file. Lightroom's preferences have the option of when to delete the largest previews, the 1:1 previews. When you delete the 1:1 previews, the size of the Previews.lrdata file is reduced. If you don't delete 1:1 previews, the previews file can get very large.
The default setting for when the large 1:1 previews are deleted is one week. The size of the preview file is reduced when these large previews are deleted, but the entire file isn't deleted unless you manually delete it. The file doesn't become huge unless you rarely or never delete the 1:1 previews, but whether it affects your hard disk depends on your available hard disk space. You can change how often the 1:1 previews are deleted by choosing Edit > Catalog Settings > File Handling (Windows) or Lightroom > Catalog Settings > File Handling (Mac OS).
Note: Do not confuse the Previews.lrdata file discussed in this technote with the [Catalogname] Smart Previews.lrdata file, which contains all your Smart Previews. In cases where there is very limited hard disk space, you may need to delete this file, but if your hard disk space is low enough that you get low hard disk errors, you should empty your trash, archive some files, and/or reoganize your data so there's more open hard disk space.
If you delete the Previews.lrdata file, previews are recreated for each folder or collection you open in Lightroom, so the first time you work in a folder, you'll experience some delay while previews are recreated.
If the option to Automatically Discard 1:1 Previews is set to Never or After 30 Days, your preview file can get very large. It can take up many GB of space. If your hard disk suddenly gets full, check the size of this file. You can then delete the file.
You may get an error in Lightroom that indicates a problem with the cache; this is another time you'd want to delete your previews.lrdata file.
If your images display with artifacts, such as colored lines, colored dots, or areas of unexpected colors, then your preview file may be corrupted, and the only way to fix this is to delete the previews.lrdata file.
Note that if you included previews of images in your catalog from images that you've archived, you'll lose these prevews as well.
If deleting the Previews.lrdata file does not solve your issue, try purging your Camera Raw cache file.
- In Lightroom, choose Edit > Preferences > File Handling (Windows) or Lightroom > Preferences > File Handling (Mac OS).
- Click Purge Cache under the Camera Raw Cache Settings.
You can also change the location of this cache by clicking Choose. Note that this cache is used only by the Develop module.