Film & Photography Lighting
Introducing FilmGrade SmoothDim technology - gradual and smooth LED dimming
When working with LED dimmers, you may notice that some provide a very smooth and gradual dimming curve, while others will be more abrupt, coarse, or be harder to get "just right." Below, we explain the technical reasons behind these symptoms and explain how our SmoothDim technology resolves this issue for film and photography lighting applications.
How LED dimming works
Virtually all LED dimmers that operate on a DC circuit (i.e. not a wall dimmer) achieve lower brightness by turning the LEDs on and off at a very fast pulse rate. Generally, the pulse rate is so fast that it is not perceived as flickering. This method of dimming is called pulse width modulation, or PWM for short.
The percentage of time that the LEDs are switched on vs off is called the PWM duty cycle. A 25% duty cycle corresponds to an LED switched on about a quarter of the time.
Typically, the position of the dial determines the PWM duty cycle.
Symptom I - LED dimmers that are especially sensitive at low light levels
The most common issue with LED dimmers is that the relationship between the dimmer dial position and apparent brightness is not linear. In particular, you may find that small changes in the dial position translate to very large changes in brightness at low light levels, while larger changes in the dial position translate to small changes in brightness at higher light levels.
This makes it very difficult to get the brightness just right, especially for dim or low light level needs.
What causes this?
The primary reason is based in biology and the way human vision works. Our eyes are actually very sophisticated visual sensors that have an extremely wide range of light intensities. We can see shadows and outlines, even in the darkest of nights, and our eyes naturally adjust to the intense light during the day.
This process is called pupillary response, and is actually partially instantaneous. In other words, as the amount of light entering our eye increases, our iris contracts, reducing the amount of light that hits our cone cells. This results in a nonlinear relationship between light energy and perceived brightness.
In other words, as the amount of light energy entering your eye increases, each additional unit of light energy creates a lesser increase in the amount of perceived brightness increase.
Therefore, a simple 1-to-1 relationship between the dimmer setting (PWM duty cycle) and light output will produce a dimming curve that does not appear even to us.
One of the core features of SmoothDim technology includes a proprietary formula that produces a mapping of dimmer dial positions to light output levels that create the perception of even and gradual dimming.
As a result, the light output appears to be even and gradual throughout the entire dimming range.
Symptom II - LED dimmers that have large dimming "steps"
Lower-end LED dimmers will be plagued by brightness levels that jump or increase erratically. The reason for this is that the dimmer dial position is translated to a particular PWM duty cycle %, but in many cases, the duty cycle value may lack sufficient precision.
For example, a low-end dimmer may only offer PWM duty cycles in 5% increments. As the dimmer dial is slowly turned on from 0%, the PWM duty cycle increases to 5%, then jumps to 10%, 15%, and so on. The 5% jump between these PWM duty cycle levels appears as a uneven "step" as the brightness is dialed up or down.
Imagine that your car can only adjust its speed in 5 mph increments. Want to accelerate from 40 mph to 60 mph? Rather than gradually increasing its speed, your car would immediately accelerate to 45 mph, then to 50 mph and so on, causing a very bumpy ride, to say the least. Low-end dimming is the same idea, with very abrupt brightness changes.
Of course, the size of the increment determines the magnitude of the effect. And, as we showed above, these large steps can represent particularly noticeable brightness differences at low light levels.
Our SmoothDim technology ensures that each step is so minuscule that it cannot be perceived by the human eye or camera lens. Specifically, we have introduced more than 65,000 different brightness steps to ensure that the dimming curve is as smooth as possible, even for the most sensitive of applications.
Find our FilmGrade LED Dimmer here.
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