Moved here from Adobe Captivate forum
Mac or windows? what version?
What viewer are you using to view the exported image?
Which color space did you export to? (sRGB is the expected web color space.)
I am using a Mac, Lightroom CC 2015, I am viewing them just in the Finder window but even when checking my Lightroom mobile app on my iPhone it shows up not the same quality as well. sRGB is what I have been using and tried the other color spaces, ending up with the same result.
What are the options you are using in the Export dialog?