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Lightning Network

9 min read

Lightning moves most payments off-chain into fast, cheap, two-party channels, settling on the base chain only when a channel opens or closes.

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A Lightning channel begins with a single on-chain transaction that locks funds into a 2-of-2 multisig address shared by two participants. From that point, the two parties can exchange an unlimited number of updated balance splits entirely off-chain, each one cryptographically valid but never broadcast unless there's a dispute.

Payments to someone you don't have a direct channel with are routed across a network of channels, hopping through intermediary nodes that each forward the payment for a small fee. This routing uses Hash Time-Locked Contracts (HTLCs): a mechanism that ensures either the whole multi-hop payment completes, or none of it does, an intermediary cannot receive funds without also passing them along correctly, and cannot steal them along the way.

Closing a channel, cooperatively or by broadcasting the latest balance if a party is unreachable, settles the final split back to the base chain in one more transaction. This is why Lightning is described as 'many payments, two settlements': the base chain only sees the channel open and close.

The trade-off for speed and low fees is liquidity management: a channel can only route as much as its two sides have locked in that direction, so well-connected, well-funded nodes are needed to route payments reliably, and a node can occasionally fail to route a payment simply because no path has enough available liquidity, even if the overall network could handle the amount.

Explain more simply

Lightning is a second layer built on top of Bitcoin that lets two people exchange many small payments instantly and cheaply, without recording every single one on the blockchain.

Think of it like opening a running tab at a bar: you settle the full total once at the end, instead of paying and recording each individual drink.

Real-world analogy

Lightning is like a network of running bar tabs connected by trusted regulars: you can pay a stranger at a bar you've never visited by routing the tab through friends of friends, and only the final totals ever touch a bank.

Key facts

  • A channel opens and closes with one on-chain transaction each; everything between is off-chain.
  • HTLCs make multi-hop routing atomic: a payment either fully succeeds or fully fails.
  • Routing capacity is limited by the liquidity locked in each channel, not just by total network size.

Common misconception

“Lightning is a separate cryptocurrency, different from Bitcoin.”

Lightning moves the same bitcoin, just off the base chain temporarily inside channels. There is no separate Lightning coin; channel balances are ultimately backed by, and settle back into, ordinary on-chain bitcoin.[3]

Go deeper

Channel state updates use revocable commitment transactions: each new balance split invalidates the previous one by sharing a revocation secret, and broadcasting an outdated (revoked) state lets the counterparty claim the entire channel balance as a penalty, this is what deters cheating without needing a trusted third party.

Because a channel partner going offline for too long without you noticing a broadcast old state could theoretically let them cheat, most implementations rely on watchtowers, third-party or self-hosted services that monitor the chain and respond to revoked broadcasts on your behalf if your own node is offline.

Newer proposals (e.g. splicing, and eventually protocols building on Taproot) aim to make opening, resizing and closing channels cheaper and more private, but fundamentally Lightning remains a network of bilateral channels rather than a single shared ledger.

Quick check

Answer every question correctly (100%) to complete this lesson.

  1. 1.How many on-chain transactions does a typical Lightning channel normally require?

    How many on-chain transactions does a typical Lightning channel normally require?

  2. 2.What do HTLCs guarantee in multi-hop Lightning payments?

    What do HTLCs guarantee in multi-hop Lightning payments?

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Extra exam questions

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16 questions

Quick check

Answer every question correctly (100%) to complete this lesson.

  1. 1.What is the Lightning Network primarily designed to solve?

    What is the Lightning Network primarily designed to solve?

  2. 2.What is a Lightning payment channel?

    What is a Lightning payment channel?

  3. 3.Does every individual Lightning payment require an on-chain Bitcoin transaction?

    Does every individual Lightning payment require an on-chain Bitcoin transaction?

  4. 4.What is an HTLC in the context of Lightning?

    What is an HTLC in the context of Lightning?

  5. 5.What does a Lightning invoice typically encode?

    What does a Lightning invoice typically encode?

  6. 6.Can a Lightning payment be routed through multiple intermediary nodes without any single node knowing the full path?

    Can a Lightning payment be routed through multiple intermediary nodes without any single node knowing the full path?

  7. 7.What limits the size of a payment that can be routed through a given Lightning channel?

    What limits the size of a payment that can be routed through a given Lightning channel?

  8. 8.What happens when a Lightning channel is closed cooperatively?

    What happens when a Lightning channel is closed cooperatively?

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Sources