Code Snippet:

#!/usr/bin/perl -w
use strict;

while (<DATA>) {
 chomp;
 if (/^(L[13].*(?:(?!TEXT).*).*)/) {print "$_\n";}
}
__DATA__
L1 04:10:07.915  LOG:   Want this Line1
L3 04:10:07.915  LOG:   Want this Line2
L1 04:10:08.024  LOG:   TEXT. Do not want this Line3
L3 06:37:58.163  LOG:   TEXT. Do not want this Line4
L3 07:02:36.921  LOG:   Want this Line5
L4 08:02:30.910  LOG:   Do not want this Line6
L5 08:02:36.943  LOG:   Do not want this Line7
L6 09:02:38.811  LOG:   Do not want this Line8
__END__  

 
Expected:
L1 04:10:07.915  LOG:   Want this Line1
L3 04:10:07.915  LOG:   Want this Line2
L3 07:02:36.921  LOG:   Want this Line5

But get:
L1 04:10:07.915  LOG:   Want this Line1
L3 04:10:07.915  LOG:   Want this Line2
L1 04:10:08.024  LOG:   TEXT. Do not want this Line3
L3 06:37:58.163  LOG:   TEXT. Do not want this Line4
L3 07:02:36.921  LOG:   Want this Line5