What do l, m and h of 198p camera mean?

In a camera, L, M and H stand for gain, L (low) stands for low, M (middle) stands for medium, and H (high) stands for high.

The video signal output by the camera must reach the standard level stipulated by TV transmission, that is, in order to output the standard video signal under different scene lighting conditions, the gain of the amplifier must be adjusted in a large range. This gain adjustment is usually done automatically by detecting the average level of the video signal. The circuit that realizes this function is called automatic gain control circuit, or AGC circuit for short. A camera with AGC function will improve the sensitivity in low illumination, but the noise will be more obvious at this time. This is because signal and noise are amplified at the same time.