Logarithmic dimming characteristic curve
In this setting, the gateway forwards KNX brightness values unprocessed to the DALI page. A logarithmic dimming sequence of the relative luminous flux results at the physical output of an operating device through the combination of forwarding the value of the gateway and the logarithmic characteristic of the operating devices. KNX status telegrams of the effective DALI brightness value are possible in this case too.
Example of brightness change:
KNX brightness: 50 % -> DALI data value (APL): 128 -> Luminous flux: approx. 3 % -> The human eye subjectively perceives about half of the lamp brightness.
KNX brightness: 75 % -> DALI data value (APL): 191 -> Luminous flux: approx. 18 % -> The human eye clearly perceives a brightness difference to the previous dimming setting. The dimming process is constantly effective.
(relative luminous flux [%] depending on the 8-bit KNX data value [0...255])
KNX brightness value | KNX brightness value [%] | DALI value (APL) | Luminous flux [%] |
|---|---|---|---|
0 | 0 | 0 | 0 |
1 | 0.4 | 1 | 0.1 |
10 | 4 | 10 | 0.13 |
50 | 20 | 50 | 0.38 |
80 | 32 | 80 | 0.86 |
100 | 40 | 100 | 1.5 |
128 | 50 | 128 | 3.2 |
150 | 60 | 150 | 5.8 |
175 | 70 | 175 | 12 |
200 | 80 | 200 | 23 |
225 | 90 | 225 | 45 |
255 | 100 | 254 | 100 |
Advantages of a logarithmic DALI dimming characteristic:
Ideal for pure brightness controls. Adjustment to the brightness perception of the human eye. As a result, brightness changes are perceived evenly in the entire dimming range. Fine number of levels in the lower dimming range.
Disadvantages of a logarithmic DALI dimming characteristic:
Difficult or even no adjustment at all at other KNX actuators that only dim linearly. Poor sliding progression when mixing colours via separate DALI channels.
In the event of operating devices with a high physical minimum brightness (> 3%) and thus a limited luminous flux range, the lower KNX dimming range (0.4...50 %) cannot be utilised.
