voltage. This is called the DC intermediate. In the second stage, a buck converter draws from the DC intermediate and regulates current to the final power electronics via an electronic control board. This control board carefully adjusts the high frequency duty cycle of its transistors to maintain optimum color and light output as the lamp ages. Finally, the regulated current is inverted by an LF-converter board that uses four Insulated Gate Bipolar Transistors (IGBTs) to switch the DC at precisely 60 Hz into a square wave AC (unlike the sinusoidal pattern of line AC). Leaders in this field include Power Gems Corp, B&S, & Mytronic. By using a square-wave output that is not referenced to the line cycle rate, a flicker-free output can be produced. Since the IGBTs switch on and off at a regulated cycle rate, a generator can be slightly off-speed and the lamp will still be flicker-free, which is not the case with a standard magnetic ballast. The square wave nature of the output results in a straight-line power output from the lamp. The time where cathodes aren't emitting electrons of high enough energy is very short, meaning that safe (flicker-free) filming can occur at camera framerates up to 10,000 frame/s on most electronic ballasts. Unfortunately, this very sharp switching on and off inherent to the square-waveform causes extremely high frequency vibrations in the lamp. A square wave can be thought of as an infinite sum of odd-numbered harmonics, which will include frequencies at the resonant frequency of the bulb, causing it to vibrate at that frequency like a bell or whistle. The lamp housing does not help this, acting as a resonating chamber that amplifies the noise and presents a problem for sync-sound recording for film and video. To correct this, most electronic ballasts are equipped with a silent mode that eliminates the higher frequencies, but rounds off the voltage transition, causing the same flicker issue with magnetics, though to a lesser extent. This mode provides safe, flicker-free filming at framerates up to 24 frame/s on most electronic ballasts. In addition to solving the problems of flicker, electronic ballasts also provide other advantages over magnetic ballasts. With a square wave voltage, the cathodes spend much more time emitting electrons and exciting the plasma, creating a gain of 5–10% in lumen output. The square-wave nature of the power flow allows lamp life to be extended by as