If you record a 60Hz on/off light with a 30fps camera, the light will not appear to be always on. The perceived effect will depend on the synchronization between the frequency of the light and the frame rate of the camera.
If the camera's frame rate is an integer multiple of the light's frequency, such as in this case where the light frequency is 60Hz and the camera frame rate is 30fps, there will be a consistent pattern. Each frame of the camera will capture either the light being on or off, but the pattern will repeat every two frames. This means that in the recorded video, the light will appear to flicker or pulsate at a frequency of 30Hz, which is half the frequency of the light.
However, if the camera's frame rate is not synchronized with the light's frequency, the recorded video may show different patterns. For example, if the camera's frame rate is slightly higher than 30fps, the light may appear to flicker irregularly or even seem like it's continuously on due to the camera capturing more "on" frames than "off" frames.
In summary, if the camera's frame rate is exactly half the frequency of the light, the light will appear to flicker at the frame rate of the camera. Otherwise, the perceived effect will depend on the specific frame rate of the camera relative to the light's frequency.