Normal deadlifts incorporate the quads into the lifting of the weight, stiff legged deadlifts lift purely from effort in the lower back and hamstrings.
Stiff leg deadlifts do place a greater stress on the lower spinal discs due to greater load concentration on the area, this makes cranking the weight up, and not using perfect form far more likely to injure you.
Other lower back exercises.
Squat: the answer to everything
works the lower back like a charm.
Good mornings: light barbell across upper back/neck (same position as squat). Legs 'soft' at knees. Bend forward from the waist/hips, keeping the spine straight till your torso is nearly parallel to the floor. Now stand up straight. Got its name as it looks a bit like someone bowing when saying 'good morning' back in the days of polite society
Hyperextension. Can be done on a hyperextension station in a gym, or can be done at home as an exact opposite movement to a weighted crunch.
Lie face down on ground, hold a weight steady on your upper traps, now arch your back, raising your rib cage off the ground as high as possible (do not crane your neck- just keep looking forward and slightly down). Hold at max contraction, then down and repeat for target reps.
Havent a name for these next ones. Not sure if I invented them, but i have not seen them done elsewhere.
lie face down on a flat weights bench, with your lower body (hips and legs) hanging off the back of it (you will need to hold the bench with your hands in line with your head).
Your position is now like you are bent over the bench, with your knees on the floor. By tensing your hips and locking in proper posture, you will raise the knees slightly off the floor. Keeping your feet together do a slow double 'back kick' straightening the legs as you thrust the feet back so that the whole body is now parallel with the floor, pause, and then 'tuck' your legs back in to the start position. When you get the hang of it, add a dumbell held between the feet.
They should keep you busy