Scrypt mining is different from SHA-256 mining in that scrypt uses a different algorithm to calculate blocks. Hashing wise scrypt is one-thousandth to SHA-256.

Example in Bitcoin, you have 10 GH/s of hashing power in Litecoin, scrypt is 10 MH/s or a one-thousandth of Bitcoin, although the proportion earn of money from bitcoin to litecoin is quite different.

Another example
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My Litecoin rigs are hashing 19.3 MH/s I earn $83.27 per day before electric bill. (That will change)

A bitcoin miner will need about 1,150 GH/s (1.150 TH/s) to earn the same amount before electric bill. (Of course that will change too later)

I am using GPUs for Litecoin mining and Bitcoin are ASIC territory obviously.

Bitcoin ASIC can only mine bitcoin and other SHA-256 coins and not scrypt coins.

There are scrypt mining ASIC but they are not worth the purchase now, cheaper to buy GPUs and GPU has a resale value compare to ASICs.