Low Frequency Square Wave vs High Frequency Sine Wave
The square wave design provides constant maximum voltage to the lamp for a longer period of time. This produces more photons of light for your plants. The lower frequency needed will not cause any issues related to RF interference. The square wave design will improve the performance of your grow lamp.
The sine wave design provides maximum voltage to the lamp for a shorter period of time. You still get the same amount of photons from the light but maximum voltage is not maintained as long as the square wave design. In order to match the photon output of a square wave ballast, the sine wave is at an ultra-high frequency of 120,000 hertz.
This makes the amount of photons produced between the two almost identical. Square wave technology is more expensive to manufacture than sine wave technology and it offers the most stable power supply to the lamp which will increase the lamps performance.