Lazy Loading Images and Iframes
Lazy loading means the browser only downloads images and embedded content when the visitor is about to scroll to them, rather than loading everything at once. The page above the fold appears faster because the browser is not distracted by content nobody has reached yet.
Used well, it speeds up the initial load without the visitor ever noticing a thing.
Measuring the Benefit
We confirm lazy loading is helping rather than hurting by testing the real loading experience, not just the headline numbers. The aim is a fast first screen with no awkward gaps further down.
- Check the first screen loads quickly and completely.
- Confirm later content arrives before it is reached.
- Watch for any layout shift as items appear.
- Verify the main image is not delayed.
Getting the Balance Right
Lazy loading is powerful but easy to over-apply. Delay the wrong thing and visitors see empty gaps as they scroll, or the main image arrives late and harms your Core Web Vitals. The skill is in choosing what to defer.
- Load the first screen of content eagerly so it is ready instantly.
- Defer only what is genuinely below the fold.
- Begin loading items just before they scroll into view.
- Always reserve space so nothing jumps as it appears.
Where It Helps
- Long pages with many images further down.
- Embedded videos, maps and social posts in iframes.
- Galleries and product listings below the fold.
Where to Be Careful
The main hero image should not be lazy loaded, because delaying it would hurt your Largest Contentful Paint score. We load the first screen eagerly and lazy-load the rest.
How We Implement It
- Apply native lazy loading to off-screen images and iframes.
- Reserve space for each element to prevent layout shift.
- Test on slow connections to confirm content arrives before it is needed.
If you need a hand with any of this, your Progressive Robot delivery team is ready to help. Raise a ticket from the Support area of your client portal or speak to your account manager and we will guide you through the next steps.