x86-16 machine code, IBM PC DOS, 13 10 bytes

00000000: b04c cd29 0c20 3403 ebf8                 .L.). 4...

Listing:

B0 4C       MOV  AL, 'L'        ; start off with capital L
        PRINT:
CD 29       INT  29H            ; write to console
0C 20       OR   AL, 020H       ; lowercase it
34 03       XOR  AL, 3          ; swap between 'l' (0x6c) and 'o' (0x6f)
EB F8       JMP  PRINT          ; loop forever

A standalone PC DOS executable COM program. Output to console.

-3 bytes thx to @nununoisy's very clever use of XOR to swap between l and o.

Runtime:

Forever and ever...