Photocell Control
i) 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.
ii) Photocell DISABLED
If the photocell is configured as DISABLED 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.
Programming the Photocell Set-points
Method 1: Manual
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’s screen briefly,
following a download operation. The number represents the light level read immediately before the download
took place.
Tip: Turn the lights off using the QuickSet Pro (UTILITIES/LightSpot_MLS-LCM/USER-REMOTE) to
measure the perceived light level with no contribution from the controlled lighting.
Method 2: ‘Teaching the Levels’
With the photocell configured as ACTIVE or PASSIVE:
1) If the lights are not already on, switch them on manually by pressin
g "+" (HC5A) or
‘UTILITIES/LightSpot_MLS-LCM/USER-REMOTE/HC5/Lu/OK’ (QuickSet Pro
)
. Fluorescent
lights do not reach full output until up to 15 minutes after being switched on, so ensure that the lights are
fully warmed up before continuing.
2) If the chosen photocell mode is Passive, wait until the time of day when the natural light level is at the point
below which you
want the lights to be on. For Active photocell mode, wait until the light level is
would
above which you
want the lights to be on.
would not
3) Start the internal self-programming mechanism by pressing and holding Scene 1 (HC5A) or
‘UTILITIES/LightSpot_MLS-LCM/USER-REMOTE/SET LIGHT LEVEL/OK’ (QuickSet Pro). The
detector takes a photocell reading, adds a small amount and stores the value in SET-POINT HIGH. Then
it turns the lights off, makes another measurement and stores the value in SET-POINT LOW. The lights
now switch on again to acknowledge a successful programming operation.
The two switching thresholds have now been set, and the difference between them is equal to slightly more
than the contribution made by the electric lighting. This is the perfect amount of hysteresis to ensure that the
lights will not oscillate.
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