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Infinity Signature Series Tech Talks – PWM Dimming


Imagine you have like one cycle in time that is a fraction of a second long "and with Pulse Width Modulation it means that if the fixture is 100% on, the fixture is 100% on of the time" If the fixture is at 50% then brightness, and I want to have 50% brightness output, theoretically without any compensation or anything this fixture would be on 50% of the cycle "If I am looking at 25% brightness it would be 25% of this time that I am looking at" Basically it's tricking our eye in seeing a source that is always the same brightness, darker by shortening the time "Because with the human eye we only recognize fluid motion after 25 pictures per second or 25Hz basically" The PWM frequency needs to be higher than that "If I am looking at the light is on for a fraction of the time of that cycle, the frequency needs to correct that" "If we are looking at lighting or LED lights while dimming for our naked eye to not see a flicker the frequency would need to be higher than 200Hz" "Cameras work a bit differently because a camera just looks at a fraction of the image" "Depending on the camera type they actually read the image from the top to the bottom" And that takes a certain amount of time "If the PWM frequency matches exactly what the camera would take for example for a frame and they are in sync" It could mean that the camera is always taking a picture when the LED light in it's cycle unfortunately is off, which is not something that we want to have We need to make sure that the LED light is a lot faster than that so we make sure that the light is always on when the camera would take pictures "That is why we need a certain amount of frequency to not cause interference with the camera" "So the Infinity fixture has a PWM range from 1,1KHz to 1,6KHz which might seem low " "But the clever thing about that is it can be incremented or decremented in steps of 10Hz" "Even if I am running into an interference or rolling shutter I can be able to adjust the PWM frequency by just a little bit " So I am just getting into what I need to have At the same time while being able to maintain that super high resolution for the dimming that we need for a smooth dimming "Very high frequency means I am having a potentially low resolution for the dimming," which doesn't give me enough headroom inside the fixture to calibrate the fixture properly and to maintain a good dimmer curve "In order to reach that and to get to the point where it's having smooth dimming" " I think Infinity chose the exactly right path to limit the PWM frequency to 1,6KHz at the end" "But at the same time this is still high enough to even work with high frequency cameras," to not show a valid flicker or do not show rolling shutter artifacts or any other issues that might occur with cameras "I think it's a very good balance between quality of dimming versus resolution"

Source: Youtube

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