According to the manufacturer the major difference between the two is that the LC-LE835U series is 3D-compatible and works with active 3D glasses (not included). See our 3D TV FAQ for more. The 835 has a 240Hz refresh rate, while the 830 has a 120Hz refresh rate. We don't expect this difference to have a major impact on picture quality. Check out the article 240Hz: What you need to know for details.
The 835 also has a glossy screen finish as opposed to the 830's matte screen, which will have an impact on bright-room picture quality. In general we prefer matte for bright rooms.
Also, the dynamic contrast ratio specification on the 835 is 8,000,000:1, compared with the 830's 6,000,000:1. We don't expect the difference in contrast ratio specification to have a major impact on picture quality, but we can't say for sure since we haven't tested the 835. Check out specifications to ignore from our TV buying guide for details.
Cosmetic differences include the 835's "dark silver" frame, light-up touch sensor, and silver stand neck. The 830 has a black frame and stand neck, and no light-up touch sensor.
Otherwise the two series should be very similar. For more information check out our full review of the Sharp Aquos Quattron LC-60LE830U.