Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 02, 2020	Jun. 30, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	nLIGHT, Inc.
Entity Central Index Key	0001124796
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Smaller Reporting Company	false
Emerging Growth	true
Entity Shell Company	false
Extended Transition Period	false
Entity Public Float			$ 633.7
Entity Common Stock, Shares Outstanding		38,362,820
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes