The Labour Corps was part of the Infantry Regiment. If you go to the website
http://www.1914-1918.net/labour.htm you will find the history of it.
I may be wrong but I think the "Dads Army" Home guard only came into existence in World War 2.
It is more likely that Henry Light enlisted in the regular army, in which case you could search for hir army record through Ancestry.co.uk