5
Photocell Control
i) Regulating Photocell
Regulating photocell control tries to maintain a constant level of total illumination in the
space controlled by dimming and brightening the controlled luminaires to compensate
for changes in illumination from other sources.
With the photocell configured as DISABLED the Regulating Control module is
influenced only by the BRIGHT-OUT setting. BRIGHT-OUT = YES allows it to hold-off
the lights at the start of occupancy if natural light already exceeds SET-POINT LOW
and to extinguish the lights during occupancy if total light, after the controlled luminaires
have been dimmed to minimum, exceeds SET-POINT HIGH continuously for a period
equal to the OFF DELAY . The lighting is restored immediately if the illumination level
subsequently drops below SET-POINT LOW.
If the photocell is configured for ACTIVE or PASSIVE control of the relay switched load
then the Regulating Control module adopts the decision made by the Switching Control
module in the case of turn-on inhibit on entry, but still obeys the BRIGHT-OUT YES/NO
setting with regard to turn-off during occupancy.
ii) Switching Photocell (PHOTOCELL: ACTIVE or PASSIVE)
Both ACTIVE or PASSIVE modes hold off the controlled lighting on entry when natural
light is sufficient, i.e. SET-POINT LOW is exceeded, but only ACTIVE mode will
extinguish the lighting if natural light increases sufficiently during occupancy, i.e. SET-
POINT HIGH is exceeded continuously for a period equal to OFF DELAY. The lighting
is restored immediately if the illumination level subsequently drops below SET-POINT
LOW.
iii) Photocell DISABLED
If the photocell is configured as DISABLED for relay Switching Control it will have no
effect on the control of that load, which will be ON continuously during periods of
occupancy unless commanded OFF via manual switch or infrared control. The photocell
readings are still available for use by the Regulating Control module while in this mode.
Programming the Photocell Set-points.
The parameters SET-POINT LOW and SET-POINT HIGH programme the detector’s
photocell response The SET-POINTS can be manually programmed as numbers
between 1 (darkest) and 1023 (brightest). This number is not scaled to correlate with
‘lux’ measurements made using a light meter, but nevertheless is a true representation
of the light level perceived by the detector. To assist with finding the appropriate SET-
POINT settings, the light level currently perceived by the photocell can be viewed on the
QuickSet Pro screen briefly, following a download operation. The number represents the
light level read immediately before the download took place.
