What Is a Light Client and How Do Light Nodes Work?

Blockchain technology is designed to be a trustless, decentralized infrastructure. Each node in the network maintains its own copy of the digital ledger and updates that copy as new blocks are added to the blockchain.

However, some participants in the blockchain may lack the resources or desire to operate a fully independent node. For these parties, a light client or light node offers a potential alternative.

Full Nodes vs. Light Clients

The blockchain ecosystem relies on the participation of a network of nodes to run the system. These nodes are responsible for storing the current state of the blockchain and updating it as new transactions come in. Without such a network, it would be infeasible to implement a decentralized digital ledger.

The nodes that do this work are referred to as full nodes. Running a full node can require significant resources and processing power. When a full node is set up, it needs to download a full copy of the blockchain’s history and verify it before it can start tracking newly created blocks. 

As blockchains’ ledgers grow larger, this can consume a significant amount of storage space.

Light clients, on the other hand, don’t maintain a full copy of the digital ledger. Instead, they only track the chain of block headers unless they’re interested in the content of a particular block. 

This creates a level of dependence on full nodes but reduces the storage and processing power required to track the state of the blockchain.

How Do Light Nodes Work?

Light nodes are designed to allow users to participate in the blockchain ecosystem without the overhead of operating a full node. Some of the key details about how light clients work include the following:

• Connections to Full Nodes: A light node will not store a complete copy of the blockchain’s digital ledger but may need access to certain data to verify transactions. Light clients will connect to one or more full nodes and query them for transaction data as needed.

  
  

• Block Header Downloads: Block headers summarize the transactions contained within a block and are what is actually “chained” together using block hashes. Light nodes will download, verify, and track this chain of block headers to provide them with visibility into the current state of the blockchain’s ledger.

  
  

• Transaction Validation: If a light node wants to verify a particular transaction, it can request the data for the block containing that transaction from a full node. Using this transaction data and the Merkle root contained within the corresponding block header, the light client can verify that the transaction in question is actually contained within that block.

In general, light nodes and light clients are designed to trade some level of security and trustlessness for greater efficiency and accessibility. By not downloading and storing the transaction data contained within each block, the light client loses the ability to perform full independent verification and is somewhat dependent on full nodes to verify transactions and provide data as needed. However, the light client has the ability to validate the data that it does download and by limiting the scope of this download, it operates much more efficiently than a full node.

Benefits and Downsides of Light Nodes

The blockchain ecosystem needs a certain number of full nodes to function. These nodes are responsible for storing copies of the blockchain’s digital ledger and performing decentralized validation of transaction data. Without them, the blockchain would not function or would become centralized.

However, if a blockchain has an adequate number of full nodes, light clients can provide significant benefits to their users, including the following:

• Reduced Storage and Processing: In general, light clients only track and verify block headers. This requires significantly less storage space and processing power than a full node.
  

• Faster Deployment: Light nodes only need to download and check block headers when being set up. This enables them to be deployed much more quickly than a full node.

• Independent Verification: Light clients can request and verify data from full nodes when desired. Connecting to multiple, independent full nodes and comparing the data that they provide can also help to ensure that the light node’s view of the blockchain is correct.
  

• Increased Accessibility: Light nodes can be used by resource-constrained devices (such as smartphones) and by users who just want to verify transactions on the blockchain. This makes blockchain technology more accessible since a potential user doesn’t need to operate a full node to participate in the blockchain and track the current state of transactions.

  
  

While light clients have their benefits, they also have their downsides. These include:

• Trust Assumptions: Light nodes rely on full nodes for access to blockchain data. While a light node can verify data to an extent, it has to trust the full node to provide data when needed.

• Block Creation: Block forging is one way for node operators to make money in the blockchain space by collecting transaction fees. Since light nodes lack visibility into past and pending transactions, they can’t take transactions from public mempools and organize them into a valid block.

Conclusion

Light clients provide a more accessible and less resource-intensive method of interacting with the blockchain. Instead of tracking and verifying every transaction performed on the blockchain, light nodes only monitor the block headers and request transaction data on an as-needed basis. This approach is easier than operating a full node but introduces some security risks and trust assumptions since the light client lacks a full view of the state of the distributed ledger and is reliant on full nodes for access to transaction data.

The choice between a light client and a full node should be based on use cases. A light client may be the right choice for a user who only needs high-level read access to the blockchain. On the other hand, if an organization is performing high-value financial transactions on the blockchain or running important smart contracts, then operating a full node may be necessary to provide the level of visibility and security required.