How do you link James Lightfoot born 1762 Luton to the family living in Clapham?
James was from Clapham when he married Jenny Crutchley in 1790 at Goldington.
James Lightfoot was 71 when he was buried at Clapham in Feb 1841 (so born 1770)
James 1762 is son of William & Sarah Lightfoot ... but they cannot be the William & Sarah that married at Luton in 1775, the subject of your other thread.
Is there any other family link for the Lightfoots of Luton to the north of the county?
No, not that I can find, but since that was all there was online I linked James to the only William and Sarah I could find. I have the Willam and Sarah that married in 1775 as James's brother and sis-in-law.
As far as I could see, William Lightfoot (1728) and Sarah Heydon (1730) married in 1753 in Luton, where they had William (1754), a stillborn child in 1757, Samuel (1758), Isaac (1760), James (1762), John (1764), Peter (1766), Edward (1768) Sarah (1770) and Ann (1774).
Firstborn William marries Sarah Farr in 1775, his brother Samuel marries Elizabeth Gathard in 1783, James marries Jenny/Jane Crutchley in 1790.
I see no reason why James can't have gone from Luton to Clapham to find work, for example. He wasn't the first son but no less than the fourth, so any family business or craft would most likely have been taken over by William, Samuel or Isaac.