What is Lazy Loading?
Lazy loading defers the loading of images until they are about to enter the viewport. Instead of loading all 50 product images on a category page at once, only the visible ones load initially.
Impact on Core Web Vitals
Largest Contentful Paint (LCP): lazy loading non-critical images reduces initial page weight, improving LCP. First Input Delay (FID): fewer resources loading means the browser responds faster to user interactions. Cumulative Layout Shift (CLS): proper lazy loading with width/height attributes prevents layout shifts.
Implementation
Modern browsers support native lazy loading with the loading attribute: add loading="lazy" to img tags. For the first visible images (above the fold), use loading="eager" or omit the attribute entirely.
Best Practices
- Never lazy load the first product image visible on screen
- Always include width and height attributes to prevent CLS
- Use placeholder images or blur-up technique for better UX
- Implement intersection observer for custom lazy loading
- Test with Google PageSpeed Insights after implementation
Image Format Optimization
Combine lazy loading with modern formats. Use WebP images exported from Pic1.ai for 30% smaller file sizes. Implement picture element with WebP and JPEG fallback for maximum compatibility.
Measuring Results
Before and after implementing lazy loading, check your PageSpeed Insights score, total page weight, time to interactive, and LCP metric. Most sites see 20-40% improvement in page load speed.