How do you justify using Stormlight-infused gems as money more valuable than dull gems? I can understand why gems - even dull ones - would qualify for currency: for the same reasons we value gold, diamonds, etc. But Stormlight itself is only valuable to beings that can use it. For most other people it's just a source of light if you don't want to use fire.
Why are Stormlight-infused gems used as a currency?