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What can Regulus Smart Lights do for you in an office environment? A lot! Since they can be addressed individually, any lighting needs can be fulfilled, simply adjust brightness and color temperature for every light and save those settings as a scene!

Here is a short video demonstrating how the Regulus smart luminaires we installed at the city government offer true lighting freedom: Any pattern, any brightness, any color temperature, just set the scenes the way you like:

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The Kaohsiung city government was rebuilding some of their conference rooms which are now equipped with Regulus smart luminaires.

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This allows them to freely decide where they want how much light at what time thanks to individually controlled luminaires.

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Several configurations have been preset for easy and quick access, but those can be changed at any time. Regulus smart lighting solutions allow you to enjoy comfort while saving energy.

I had already explained why a LED bulb itself can be the source for flicker at low power levels. There is another source: the dimmer.

triac_dimmer

The component that allows us easy dimming of devices consuming much power is called a "triac". The circuit above is a very simple dimmer, the blue line shows how the current flows through triac and lamp.

Pin 3 is where a triac is initiated, switched on. It can not be switched off there, only switched on. The only way to switch a triac off is by disconnecting the supply voltage. This is why you seldom see triacs in DC applications, mostly in AC devices.

triac_sine_wave

In AC, the voltage will rise and fall again, passing through a "zero crossing", where the voltage is zero. The image above shows those as "ZC".

So how can a triac reduce power consumption? It is switched on a while after the zero crossing, when there already is a certain voltage. It stays switched on until the next zero crossing. In the image on the right, the triac waits until the grey area has passed, then it is switched on. The energy in the grey area is not used now. The later the triac is switched on, the less energy a device can consume.

I must correct something: During the zero crossing, it is not the lack of voltage that switches the triac off, it is the lack of current. Every triac has a so-called "holding current". If the current through the triac goes below this threshold, the triac will switch itself off. And here again our energy consciousness is causing technical trouble:
Suppose we want to replace two 60W incandescent bulbs. At 220V, they may have consumed 550mA. Now we use two 8W LED bulbs instead, which may consume only 75mA, a more than sevenfold reduction. If we reduce the power on these LED bulbs to 10%, we may end up with only 7.5mA current.

So what happens then? The current going through the triac is lower than its holding current, it switches itself off. The capacitors in the bulbs are drained, so they are charged with the next wave and the triac stays on, only to switch off again when the current became too small. The result is flicker, again.

A few years back, Philips had a list on their website with recommended dimmers for their LED bulbs. If you went through the list you would find that they were all 250W or 125W dimmers, for very little power. The reason is simple: A smaller maximum current usually also means a smaller holding current.

A good way to avoid this problem is to supply LED light sources with a constant stable voltage and use an interface to tell the light source what output power to use, something we do in our Regulus smart luminaires.

We take a lot of things for granted, especially in areas we are familiar with, but do not understand very well. One such case may be flicker on dimmable LED bulbs. My incandescent bulb did not flicker, so why this modern one?

There are two possible sources for this problem, I would like to show the one inside the LED bulb. Incandescent bulbs are basically just a resistor, a wire resistor, and resistors do what they can best (resisting) down to zero volt in a very smooth way.

LED_driver_circuit

LED bulbs are different, because they include driver electronics, they are electronic devices. You can see one in the above image. This is not the whole schematic of a bulb, but the part that is important to understand the problem.

LED_driver_block

This is a TS19450 by Taiwan Semiconductor, but other driver ICs work basically the same way: A pretty high voltage of sometimes up to 600V is connected to the pin Vin. As you can see in this image, there is a voltage regulator inside the chip, because the IC needs a stable operating voltage (VDD). This one requires about 7.5V at VDD.

So what happens when you use a triac dimmer to dim this bulb down? The voltage at Vin goes down. The IC needs at least 7V, the regulator needs a few more volt to operate, so when we get to about 10V at Vin, the IC can not operate properly any longer. It will switch itself off, because there is not enough voltage, then switch on again, because the capacitors had been charged a little again, then switch off again - the bulb will flicker.

Turn the dimmer down a little more and the bulb goes off completely, earlier than an incandescent bulb. This is because we are reducing the operating voltage for an electronic device, not for a resistor. A solution to this problem would be to add an interface to the circuit, always run it at optimal voltage, and use commands on the interface to regulate the power output - as we do in our Regulus smart luminaires.

Some manufacturers design the circuit so that the bulb will switch itself off completely before it can flicker. Look up datasheets or flyers for such bulbs, they will often advertise a dimming range of "10-100%". So don't be surprised if a dimmable LED bulb flickers at very low power, that is very normal.