LES stands for Light Ethereum Subprotocol and is described at length here.
LES allows to easily synchronize the chain, at the cost of running transactions in the EVM, and relying instead on merkle proofs.
LES is partially implemented by Apache Tuweni. Account data is not yet available.
Scope of work
Implement merkle proofs for LES
Implement, if that makes sense at all, the budget mechanism that allows a form of rate limiting for LES.