Looking for logging into the Lightning User site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Lightning User site. After that you can login as usual with your login credentials.
https://help.salesforce.com/apex/HTViewHelpDoc%3Fid%3Dsecurity_ll_enable.htm
https://help.salesforce.com/apex/HTViewHelpDoc%3Fid%3Dsecurity_ll_enroll.htm
https://success.salesforce.com/answers%3Fid%3D9063A000000ifgJQAQ
https://www.youtube.com/watch%3Fv%3D_Vfwp3TGtUM
https://www.youtube.com/watch%3Fv%3DTQOF61kaRXM
https://www.adminhero.com/lightning-login/
http://www.google.com.ph/url?url=http://sanjaykeynotes.blogspot.com/2017/06/log-in-password-free-with-lightning.html
https://www.salesforceben.com/lightning-login-fingerprint-access-salesforce/
https://www.slideshare.net/MichaelSmith138/salesforce-lightning-login-dreamforce-2017
https://salesforce.stackexchange.com/questions/136083/how-can-you-can-assign-the-lightning-experience-user-permission-to-a-set-of-us
https://www.simplysfdc.com/2017/03/salesforce-introduce-lightning-login.html
https://automationchampion.com/tag/log-in-password-free-with-lightning-login/