Lightroom uses numerous kinds of previews and caches for different purposes. Having a basic idea of their usage can help you pick the right ones for your needs. The main ones you need to know about are rendered previews and smart previews. To fully understand the Library & Develop preview loading logic to optimize your preview choices, see the diagrams on pages 503 & 506 of Adobe Lightroom Classic – The Missing FAQ. In this post, we’ll cover the basics for Previews and Cache.
Library module
Standard-sized rendered previews are the most frequently used previews. They’re used to display the photo in every module except Develop (where they’re shown briefly and then replaced with cached raw data). For speed, Lightroom stores a range of different size previews, from thumbnails right up to your chosen preview size.
The size and quality of the standard sized previews is set in the Catalog Settings dialog. Go to Edit menu (Windows) / Lightroom menu (Mac) > Catalog Settings > File Handling to check and change the settings.
The best size setting depends on your general browsing habits and on your screen resolution. Choosing a size about the width of your screen is a good starting point, and the default Auto setting does this automatically. If you always leave the panels open and your hard drive space is very limited, you may prefer a slightly smaller size.
The quality setting is, as with most things, a trade-off. Low quality previews take up less space on disc as they’re more compressed, but higher quality previews look better. The default, Medium, is a good compromise.
1:1 rendered previews are full resolution Adobe RGB JPEGs, so they take up more space. If you want to zoom in on your photos in the Library module (e.g. checking focus), it avoids Lightroom having to build 1:1 previews on the fly, which would slow your browsing experience. Note that they don’t have any effect in the Develop module, which works with raw data instead of pre-rendered previews.
If you’re concerned about the disc space that the 1:1 previews take up, you can choose to have them automatically deleted. You can select this to happen after 1 Day, 1 Week, 30 Days or Never. Go to Edit menu (Windows) / Lightroom menu (Mac) > Catalog Settings > File Handling to check and change this setting. Alternatively, you can discard 1:1 previews on demand by selecting the photos and choosing Library menu > Previews > Discard 1:1 Previews.
There are multiple ways to build standard or 1:1 previews:
- On Demand – The standard sized preview is automatically built when you view a photo in the Library module. The 1:1 preview is rendered when you zoom in. The problem with waiting for them to build on demand is you’re sat staring at a Loading overlay while Lightroom builds the preview. Of course, this slows down your browsing. To avoid this delay, you can build the previews in advance.
- On Import – In the File Handling panel of the Import dialog, you can choose to build Standard or 1:1 Previews immediately after import. The other options in the Preview pop-up – Minimal and Embedded & Sidecar – only extract previews embedded in the image file, leaving Lightroom to build its own previews on demand.
- Menu Command – If you select the photos in the Library module, you can select Library menu > Previews > Build Standard Sized Previews or Build 1:1 Previews. This is particularly valuable, as you can leave Lightroom building these previews at a time when you’re not using the computer. It can also be used to update existing rendered previews when you’ve made Develop changes. It automatically skips any previews that are already up to date.
Develop module
Temporary Caches – Lightroom also uses a selection of temporary caches to improve performance, especially in the Develop module. The most useful of these caches is the full resolution pre-load, which happens automatically behind the scenes. When you’re working in the Develop module, it preloads some photos either side of your current photo. This means that when you move on, it loads much quicker. This happens automatically, so you don’t need to do anything to benefit.
Smart Previews are lower resolution (2560 px long edge) partially processed raw data, and can be used in place of the original files. They behave like the original raw files when editing in the Develop module, except they’re smaller, so they’re a lot less taxing on the computer’s processor. They also help to speed up face recognition and mobile sync.
To build smart previews, check the Build Smart Previews checkbox in the File Handling panel of the Import dialog, or after import, select the photos in the Library module and go to Library menu > Previews > Build Smart Previews. If you decide to delete them later, perhaps because you require the disk space, you’ll find Discard Smart Previews under the same menu.
To use them to improve Develop performance, simply go to Preferences > Performance and check Use Smart Previews instead of Originals for image editing. When you zoom into 1:1 or export the photos, Lightroom’s smart enough to switch to the full resolution original.
Camera Raw Cache (aka ACR Cache) temporarily holds partially processed fast load data for the most recently accessed raw files. It’s used in the Develop module to speed up loading times, although other optimizations have largely replaced it now.
You can set the size of the cache in Preferences > File Handling tab. The pixel dimensions of the cached images vary depending on your standard preview size. 5-10GB is plenty for most people, but if you have a high resolution monitor, you might want a bit more cache space.
Preview Area Size
Finally, the size of your preview in the Develop module makes a significant difference to the interactive performance. The lower resolution the preview, the fewer pixels Lightroom has to compute, and the quicker it runs. If you don’t mind a smaller preview, you have a few options. You can reduce the size of the Lightroom window, enlarge the panels to make the preview area smaller, or simply select a smaller zoom ratio (e.g. 25%) in the Navigator panel.
There are further tweaks you can make during your normal workflow to improve Lightroom’s performance. We’ll discuss these in the next post, workflow tweaks.
For extensive information on Lightroom Classic, see Adobe Lightroom Classic – The Missing FAQ.
Note: purchase of these books includes the first year’s Classic or cloud-based Premium Membership (depending on the book purchased), giving access to download the latest eBook (each time Adobe updates the software), email assistance for the applicable Lightroom version if you hit a problem, and other bonuses.
We also have a special bundle offer for the two books. This includes Premium Membership for the first year as described above for the whole Lightroom family!
Originally posted 10 October 2016, updated June 2021.
Dear Victoria, I believe you are the person who can help me with this matter.
I have a very large LR catalogue which, because of the large number of photos, creates a 450GB previews.lrdata.
Is there a way to reduce this file size? I have read your above suggestions, I think there is something else I should do in my case. I am thinking even deleting some of the folders inside the container of the lrdata file, even if that would mean I would not have any previews for those file when the external HDDs are disconnected.
Any idea?
Thanks, Serban
Don’t delete files within the previews.lrdata, but you can delete the entire previews.lrdata and then choose which photos you want to build previews for. Also, check what size previews you’re creating, as the automatic size is often overkill if you usually have the side panels open.
Thanks Victoria
I goofed moving files from one cloud storage (Dropbox) to another (OneDrive), and made use of backup to get things back to where they were. My issue is that now, in library grid view, no previews are immediately viewable; only a grey box. They then slowly paint up until the screen is full of images. However, I’m scrolling & scrolling down through the library to get them to do this. Is there another way? ‘Cause, this is taking forever.
Check two things:
1. That the place you have your catalog and previews in Dropbox is permanently held locally (not the Smart Sync option that only downloads on demand)
2. Ensure Standard Previews have been built for all the photos.
In my experience the ACR never seems to exceed about 80% of its allotted capacity. If it gets to more than 3/4 full then I expand it by half and it quickly uses up more than it had done previously. If it never reaches 3/4 full then it probably does not need to be expanded.
I find it beneficial to have the things that are mostly written to on a different physical drive from the things that are mostly read. Even more so if the reading and writing are happening at the same time. My catalog and preview caches are on a separate SSD from my image files because the image files get written once but the preview caches – in a database – get modified more than once. My ACR cache is on a separate SSD from my LR-specific preview caches.
I expect this configuration would be even more significant with HDDs than SSDs. However, in my case it matters even more because I tend to flit about throughout my LrC library rather than work on a consolidated bunch of files that were loaded next to each other in a single import. e.g. accessing files by keyword instead of date is likely to find a greater spread of files that would cause more HDD head thrashing and hence slower reading. The faster the computer is the more I seem to notice such delays.
Hi Victoria,
First of all, many thanks for a great website, I do appreciate all your insight in this not so easy field..!
Now, I have tried to find a solution to the following problem without any luck however, and would be really grateful if you can point me in the right direction.
When I’m loading images from my memorycard,into my MacBookPro to Lightroom 4, it says “there’s no preview available for this file”. This at the same time as I can see the file number in each picture, but not the picture itself. I have checked the settings for the catalogues but can’t see that anything is wrong.
I have read somewhere that I can just throw away the preview catalog if it’s “acting up”, but haven’t dared to do that yet. (Read that a new catalog is being created automatically?)
I have 832 MB in my preview.lrdata catalog from what I can see, and have 500 GB available still.
I have installed Lightroom Classic CC but not yet started working in the program/imported the catalogue/s as I need to find some “lost files/images” before I do that, (as I understand it is more complicated to find/add “misplaced” files after importing the catalog.. Have a new computer and have moved the content from the old one).
Therefore I’m still working in Lightroom 4, and hope to through your guide be able to locate the images “gone astray”.
Keeping my fingers crossed that you can give me some advice on how to solve/find my missing preview!
Many thanks,
Monika
No preview in the import dialog means Lightroom can’t access the preview from the file. The Previews.lrdata won’t have anything to do with that. Lightroom 4’s really old, so I would assume it’s probably an incompatibility with the operating system that will likely be fixed by using LR Classic instead.
I would go ahead with the upgrade and then fix your missing photos. The process is essentially the same, so as long as the photos moved to the new computer, you should be fine.
Thank you Victoria ! Very useful informations! Congrats for your website!
They’re all fast drives, so that sounds great. There is already a diagram of which previews get used where on pages 461 and 464 in the Lightroom Classic Missing FAQ book, that would help you determine which ones will be best for your workflow. There’s a whole chapter on performance in there, as everyone’s workflow is slightly different.
Hi Victoria, love your site, and thanks for staying so engaged in replying to comments. I have a question if you don’t mind. I have my Library Catalog and Preview Files stored on my local Mac SSD, and the Lr Photos on an external Thunderbold 3 SSD RAID, with a Thunderbolt 2 Raid 5 backing that up with mirror at night. Is this the best way to locate the Catalog and Previews? I recall Adobe telling me this years ago and it’s what have been doing ever since. I am considering building 1:1 smart previews also, is this a good idea (space is no issue) because often when I zoom in to check focus I have lag, I am trying to speed things up as much as possible. Some sort of best practice for performance, best practice for simplicity, type of infographic would be ace. Happy to help you make those free if you sketch them out and would like those. Thanks again, Andy
Thanks a lot!
Do you know, if Lightroom uses the smart previews in the Library module if there are no regular previews already generated?
If the originals aren’t available, then yes, it’ll use the smart previews to generate the standard previews.
Hello from beautiful Santorini Greece,
Can you please help me? I have an iMac late 2015 Retina 5K model with 4 GHZ intel i7 and 40 GB of ram and it performs extremely slow compares my older iMac which is iMac (27-inch, Late 2012) 3,4 GHz Intel Core i7 and 32 GB ram.
Why my new machine is so slowly. Can i do something to make it work? Thanks in advance.
Hi Vangelis, sorry, I didn’t see your comment. The screen resolution will be a factor, compared to your old iMac with the standard resolution screen. If you haven’t already done so, the latest Lightroom Classic release has made some big strides on performance.
So ive been reading that its best to keep previews and/or cache files on a separate SSD from the working catalog. Have you heard that theory? Is there any weight to that change making things smoother
I’ve heard the theory, but it’s an unofficial hack with very minor benefits and more potential problems.
Hi Victoria. Great article, thank you.
I have some questions. If i edit using only the Smart Preview to make edition faster, what do i have to do latter. Just put the original file to it’s place and export? Would there be any changes on the image size resolution? What’s your advice?
On older versions, you have to put the originals back before you export. On the latest version (the one with the checkbox in preferences), you don’t need to do a thing as it automatically uses the originals when exporting.
Very helpful, when using “f’ key to display full screen on my iMac 5k, I always get an image using a subset of the screen. Question, what do I need to set in order to fill the screen with the image ? I’m a subscriber and had purchased your E-Books. Willy chiu
Hi Willy. My initial thought is that the original image is too small for the high resolution screen. What size image are you trying to view?
Hi, my images came from Nikon D500 and also from Fuji XT-2….however, before I made changes to Sierra MacOS, they were fine so I am not sure how settings from the OS and from LR affect each other… ? I tried ‘Slide Show’ feature and got nice full screen display.
I also have a 2011 MacBook pro laptop, current LR version and Sierra macOS, I got full screen using ‘f’ key to display in Library or Develop modules…so you may have a point about iMac5k’s higher resolution display…what settings should I check or reset to display full screen ?
BTW, your website and content is the best on LR…
Looking forward to your reply…
Hmmm, if you’re seeing a difference between Sierra and your previous OS, report it at the Official Feature Request/Bug Report Forum at http://feedback.photoshop.com/photoshop_family (with that regression noted) so the engineers can compare. I don’t remember how it worked pre-Sierra, so it certainly could be a bug.
This is a very helpful article. Thanks for sharing.