Have recently installed some additional motion/photo-cell sensor
operated outside fixtures.
The sensors are rated to control up to 300 wattts. We have equipped
them with two regular 75 watt flood lamp bulbs each. (150 watts).
The literature clearly says "Use only incandescent bulbs".
But has anybody actually tried, probably at risk of ruining the sensor
module? a CFL or CFLs.?????
Another reason for asking is that am going to try using a very small
115 volt transformer in parallel (low reactance hopefully) with the
bulbs; thus the low voltage from the transformer run to another
location then used to sound a buzzer etc. As a warning that the lights
have operated for some reason (usually unexpected human activity)
outside the house!
PS. You can set the sensitivity of these things so that not every
prowling cat or varmint operates the sensor. Only larger bodies such
Be interested in any comments or ideas. TIA
There must be some reason they specify incandescent, but every motion
sensor I've dissected used a relay to switch the load on and off. I
have no idea why a relay would be sensitive to the type of load, except
if there's some excess initial current draw.
Both of my current detectors emit a nice loud 'click' when they trip,
and it's pretty much certain that it's a relay operating.
I'd say -- go ahead and screw in a CFL. If it blows up, it's cheap
entertainment. If not, you're all set.
Yeah as other poster said, if it clicks then you can probably use the
CFL just fine because it's a relay, if it doesn't click then that
means it's being switched with a triac and for some reason they dont
want you to use a CFL. But I understand some newer CFL's are made to
be switched with triacs, they are called "dimmable" CFL's, maybe use
one of those.
Yes, and it didn't work. The CFLs flickered -quite a bit- when screwed into
sockets controlled by a motion-sensing switch, when they worked fine in
sockets with normal switches. Didn't harm anything, but CFLs could not be
The mfgr knows their product; stick with incandescent.
the secret is if the output switching device is a relay,
thermal relay, or a solidstate device.
You can tell by the wiring, relay/thermal relay is operated
from the AC line and will have THREE wires, black(hot),
white(neutral), and red(lamp load). It will directly
connect the red to the black when "dark", you can hear a
relay "click" but the thermal relay will be silent and
delayed as a small heater heats a bimetal set of contacts.
Without being connected to anything, an ohmmeter will show
the black and red to be a direct short. the photo cell only
powers the relay while in daylight, the relay actually
"opens" the contacts, turning off the light. backwards from
what you might have expected. they also usually have a high
current rating like 15A.
Solid state devices are TWO wire, black and black, or black
and red. It is wired in SERIES with the hot line and the
lamp. This creates two problems, while "off" the cfl isn't
enough of a load to provide the few volts the ss device
needs to properly operate. This causes the output to pulse
on and off, beating the crap out of the cfl until it fails.
And even when "on" the cfl can't provide a stable voltage to
keep the ss device in "on" mode while operating, sometimes
only providing half wave DC to the cfl.
Cfl's only like fullwave AC power fully "on" or completely
'off'. Anything else and the two fight each other until the
cfl just fries itself. these devices will have a minimum
wattage(load) like 5-20 watts, and a maximum like 600 watts.
There are ways of making a "safe" ss device that switches
just like a relay, but that would require 12 components vs
the 4 used now, and there MUST be a neutral wire connection.
And no one would pay for them ;-)
-larry / dallas
Thank you very much indeed to Larry and others for the detailed info.
Learnt a lot. The comment about insufficient load through a 'ss only'
device makes sense; similar to solid state programmable thermostats
that specify a minimum of say 500 watt heater load to ensure enough
voltage to operate the device.
Ours sensors controlled fixtures do indeed 'click' (you can hear them)
so figured there was relay in there and relays don't like inductive
loads very much, cos sparking at the contacts erodes them. But we are
switching AC here anyway (not DC through say an inductive load!).
Again ours with black live and white neutral 'in' and red switched
live 'out' also seems to confirm that they are a relays.
Also realised that the sensor alone would make a good security device
to set off an alarm. Think I'll acquire some more of these devices!
Many thanks for the useful discussion.
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