For DALI projects, two Kinds of dimming curves you should know

Situation like this sometimes occurs: the Dali driver manufacturer and the Dali dimmer manufacturer claim that their products have good dimming effect, but when you use them in one system, you find that the dimming effect is not as good as expected. After carefully analyzing the application situation, our technician solved the dimming problem easily by modifying the dimming curve setting of LED driver on DALI software.

What’s going on? This article will tell you a “little secret” about “dimming curves” of DALI driver. 

Before reading the following text, it’s necessary to explain the meanings of several coordinate variables, and this article only analyzes the effect of smooth DALI dimming.

1-254 signal: the control signal of dimmer, varying among 1-254

Dimming signal: the output signal of dimmer, varying among 0-100%. The driver receives this signal and executes accordingly.

Light effect: the change of light fixture’s brightness among 0-100% (here only refers to the light fixtures under dimmable drivers’ control)

The connections among them are as follow:

Now we can go to a further sharing.

In LED lighting, dimming curve is important to achieve the better light effect. In LED drivers, dimming curves can be classified as “linear dimming” and “logarithmic dimming”

Linear curve dimming of driver: the dimming signal received by the driver is linear with the impact of driver on the light effect.

Logarithmic curve dimming of driver: in the range of low dimming signal, the impact of driver on light effect changes slowly, while in the range of high dimming signal, the impact on lighting effect changes rapidly. So the curve is logarithmic.

Some people may say, "the logarithmic curve dimming effect of the driver performs better". Is it true?

Before explaining which dimming curve works better, we need to introduce another concept - the sensitivity of human eyes to light.

 It can be seen from the above figure that when the actual brightness of the light is very low, human eyes can feel and even magnify the brightness by very slight changes. For example, the actual light brightness changes from 0% to 1%, but the human eyes perceive that the brightness changes from 0% to 10%. However, when the actual brightness changes more than 50%, the perception of human eyes tends to be gentle and can not feel the subtle change of the light.

Therefore, in order to conform to the perception mode of human eyes, the best change effect of the light effect is to change slowly at low brightness and fast change at high brightness. That is, when we use the dimmer to adjust the light, the change curve of the dimmer and the light effect should be as shown in the figure below.