In a recent Facebook post, Eric Cheng asked for clarification on the Gates GT14 Underwater Lights regarding flicker frequency, and if it would affect high speed imaging.
The answer is *none*. The GT14’s have a constant light output, free of anything that would affect motion imaging. And there is good reason for this.
Background: Controlling light output of LED’s is commonly achieved by PWM – Pulse Width Modulation. Power is applied to the LED for only a fraction of second – then turned off, and back on again. 100 times each second is common. The longer the ‘on’ pulse (called the Duty Cycle), the brighter the light. Very straightforward, effective and easy to implement.
Our eyes cannot see this pulsing, the result of human ‘persistence of vision’. This is why we see a movie projected at 24 frames per second as smooth and pleasing. We don’t see PWM, but a camera does, and readily. At 24 fps (or higher), a varying amount light reaches each frame, exposing it differently from the rest. This shows up as ‘flicker’. And it’s bad, a definite image killer.
So instead of using PWM to control light levels, the Gates GT14’s employ a simple DC current adjustment up / down for this purpose. We also control the current very, very closely so the light does not vary during a shot or as the battery depletes. From full battery to exhaustion, any given light level will remain constant and flicker-free. Side note: this approach to light control usually means heat losses and less burn time on a battery. But not the GT14’s, which are very efficient at DC current control with very little heat loss, even at the highest power levels. It’s an effective and robust design.
