Specifications

T4
T4.29
Digital timers
Galax LSS
Light sensitive switches
Function and range
A light sensitive or twilight switch is an electronic
switch that switches its output-contact based
on the intensity of the ambient light, measured
by a photocell.
For DIN-rail mounting, a 1-channel, 2-channel and
1-channel with integrated digital timer are available.
They all have a separate photocell delivered
with them.
For wall mounting, an all-in-one device, integrating
the photocell, the amplifier and the switch (relay)
itself, is offered.
Operation
As long as the light intensity is above the switch-on
threshold value, the output relay remains de-
energised and the output contact is open
(see
1 in fig.1).
Once the light intensity drops below the switch-on
threshold value
4 and stays below this threshold
value during time td, after td, the output relay is
energised, and the output contact switches over
(see
2 in fig.1).
When the intensity of the light rises above the switch-
off threshold again,
5 again after a delay td the
output relay is again de-energised (see
3 in fig.1).
In order to avoid unstable behaviour, a hysteresis
exists between the switch-on and switch-off
threshold. Also a user pre-settable time delay t
d
(0..100sec), both at switch-on as well as at switch-
off, further reduces the chance of unstable behaviour.
Applications
User adjustable hysteresis
In case the built-in hysteresis does not respond to the
users’ requirements, by using a 2 channel light
sensitive switch, the on- and off-threshold can be set
completely independent of each other (see fig.2).
load
time
hysteresis
Lux
fig.1
A
Light intensity > 450 Lux
Both channel 1 and 2 are in their de-energised
position; K1 doesn’t pull and the lamps don’t light-up.
B 450 Lux > Light intensity > 150 Lux
Channel 1 switches over while channel 2 stays
de-energised. The lamps still don’t lit-up.
C
150 Lux > Light intensity
Now also channel 2 switches over, energising K1,
lighting up the lamps.
D 150 Lux < Light intensity < 450 Lux
Channel 2 is de-energised again, but K1 stays
energised through channel 1 of the light
sensitive switch.
E Light intensity > 450 Lux
Channel 1 is de-energised again, K1 is no longer
energised and the lamps are no longer lit-up.
Light sensitive switch in combination with a
staircase switch
Figure 3 shows the correct way of using a light
sensitive switch together with a staircase switch.
This application is typically useful when throughout
the day normal daylight enters the staircase and
artificial light is not required.
Preferably the output contact of the light sensitive
switch is in series with the coil and not with the load
of the staircase switch for following reasons:
- manual override at the level of the staircase is still
possible,
- in case the operating push-buttons have indicating
lamps, one can easily see if the staircase lights
can be operated or not.
fig.3
fig.2
450
150
Channel 1
450 LUX
Channel 2
150 LUX