TUL Controller expressed concern regarding the poor functionality of the tower light guns.

Narrative

I was working Local Controller in the Tower when the RADAR West position called on my shout line and told me that a Cheyenne II was NORDO and would enter the downwind to land Runway 18L; and that we could hear the pilot transmitting to us; but that the pilot could not hear us. The pilot entered the downwind and reported on my frequency and advised me of what he was doing. I transmitted to the aircraft but the pilot did not receive it. The pilot reported turning base; and then final. I was shooting a light gun signal to the aircraft the entire time and the pilot even said he was looking for a light gun signal. But he never saw the signal we were shooting him. I even sent a guy out on our catwalk to shoot it to the aircraft while he was short final to see if it would help but it did not. This is dangerous! At the time I had aircraft holding short of the runway and a vehicle doing a field inspection. The aircraft landed without anything happening. There are many times at TUL when we have vehicles on the runway; the runway is NOTAM'd closed and we would not be able to get everyone off that particular runway so aircraft would be shot a RED light. Our light gun is terrible! I've shot light gun signals numerous times to aircraft and vehicles at night and not once have they reported seeing it. This is dangerous! Tulsa has never had a light gun that works and it needs to change before someone gets injured or killed.