We've seen how motion detectors (PIRs) turn on lights when someone approaches. But what about atmospheric, architectural lighting? You want wall sconces, tree lights and pergola lights to stay on all night to highlight your home.
Remembering to turn the switch on every dusk and turn it off every morning before leaving for work is a chore that usually results in leaving the lights on all day, wasting electricity.
The solution to this problem is the oldest, most reliable and cheapest form of home automation: the Photocell or Twilight Switch. As engineers, we consider it a "must-have" for any outdoor space. Let's see how it works and, most importantly, how to avoid the annoying installation error that makes your lights...flash like a disco.
At the heart of a photocell is a small electronic resistor called an LDR (Light Dependent Resistor).
Its logic is shockingly simple: The "eye" of the sensor continuously measures the ambient light (in LUX units). When the sun goes down and the light drops below a certain threshold, the board gives a command to the internal relay. A "click" is heard and the circuit closes, providing power to your garden lights. At dawn, as soon as the "eye" sees the first rays of the sun, it does the opposite and extinguishes them.
Many customers ask us, "Why not just put a timer on the panel to turn on the lights every day at 7pm?"
The answer lies in astronomy! In Greece, in December it gets dark at 17:15, while in July it gets dark at 21:00. If you have a timer, you'll need to open your panel every 2 weeks to reset the times, otherwise in the summer your lights will be burning power for 2 hours while the sun is shining. The photocell, on the other hand, is "set-and-forget". It faithfully follows nature and the changes of the seasons without any intervention of yours.
Depending on your home wiring, there are 3 ways to incorporate this automation:
This is where 90% of photocell installation failures lie.
Imagine the following scenario: You place the photocell directly under the outdoor sconce (or opposite a spotlight).
This feedback loop creates a nightmarish "strobing" that will burn out your bulbs in no time.
The photocell should face the natural sky light (ideally North or East so that the direct midday sun doesn't hit it and "bake" its plastic) and should NEVER see the light from the lamps it controls! Also, keep it away from street lights (street light poles), as it will get confused.
Almost all photocells have a small adjustment dial that says LUX (usually 5 to 50 LUX).
The photocell is an inexpensive (from €15 to €40) but key upgrade. Position it properly so it doesn't self-blind, clean it with a cloth once a year (because dust blocks the peephole and makes it light up sooner), and enjoy a garden that magically comes to life every night, without ever touching a switch again.
Next Step: Now that our system is turning itself on, it's time to see what exactly is turning on. How do we place the fixtures to make a simple plastered or stone wall look like a work of art? Continue to our technical guide: Architectural Up-lighting & Down-lighting: Techniques to highlight stone or wall texture.
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