iPads with Retina display are a bit heavier and thicker than their predecessor, the2. This is mainly due to the larger battery and dual-LED backlight needed for the Retina display. The iPad 5 goes according to news website CNET, however, again a lot lighter and thinner.
The site relies on analyst Paul Semenza, working at NPD DisplaySearch. He claims to have evidence that Apple improved LED technology use. This new technique could dual-redundant LED backlight, making the iPad more efficient use of energy can go. The analyst cites sources within the supply chain of Apple. DisplaySearch moderately reliable source.
iPad 5 can be made thinner and lighter because the screen takes up less space. In addition, it is expected that a smaller battery is needed, the new LED technology would also energy efficient.
It is not the first time Apple has a device much thinner and lighter. The5 is the latest example of a considerably thinner and lighter, yet more powerful device.
It is still unknown when Apple will announce the iPad 5 at. Photos of a thinner, on the iPad mini inspired design leaked out earlier. In the rumor mentions an announcement in April.