Linear dimming characteristic

In this setting, the gateway linearises the DALI dimming characteristic by converting all brightness values, which are received from the KNX and configured in the ETS, appropriately into DALI data values. Thus, the KNX brightness values form linearly on the luminous flux emitted by the DALI lamps. The gateway itself does not dim linearly in this setting. A linear dimming sequence of the relative luminous flux first results at the physical output of an operating device through the combination of the non-linear conversion of the gateway and the logarithmic characteristic of the operating devices.
Status telegrams of the brightness value are also adjusted by conversion. On account of the internal calculation process, there may be slight deviations between the specified and fed back brightness value (e.g. specification = 50% -> Feedback = 49%).

Example of brightness change:
KNX brightness: 50 % -> DALI data value (APL): 229 -> luminous flux: approx. 50 % -> The human eye already perceives intense brightness.
KNX brightness: 75 % -> DALI data value (APL): 243 -> luminous flux: approx. 75 % -> The human eye hardly perceives the brightness difference to the previous dimming setting anymore. The dimming process appears unsteady.

Advantages of a linear DALI dimming characteristic:
Adjustment to existing KNX actuators possible. KNX dimming actuators or 1-10-V control units normally convert brightness values linearly into a physical output signal as defined in the KNX specification "Scaling" (DPT 5.001 / 0...255 -> 0.4...100 %). If a DALI system with such KNX actuators is combined in an installation, it is normally necessary to set a linear dimming characteristic in the DALI gateway in order to adapt the dimming behaviour to the other actuators. Otherwise, the lamp will dim to a different brightness with identical KNX data values.
A linear dimming characteristic also has a positive effect on a multichannel RGB colour control, especially during dynamic colour changes (e.g. control of 3 different DALI channels for RGB colour mixing). By converting the KNX data values to a linear luminous flux for each primary colour, colours can be mixed reliably in a wide spectrum by the lamps.
In the event of operating devices with a high physical minimum brightness (> 3%) and thus a limited luminous flux range, a linear characteristic curve allows the possible KNX brightness range (0.4...100%) to be utilised usefully in the lower dimming range due to the increased DALI data values.

Disadvantages of a linear DALI dimming characteristic:
Dimming operations are not adjusted to the brightness perception of the human eye. This means that the dimming behaviour for mere brightness control is perceived as uneven due to the logarithmic human perception.