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Enlightenment is our Profession
Enlightenment is our Profession
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Why dimmable LED bulbs often flicker (the dimmer cause)

I had previously mentioned causes for LED bulb flicker when being dimmed to very low power, that was the cause from within the bulb. There is another one, directly inside the dimmer.

The component that allows easy and cheap dimming is called a "triac", you can see a very simple dimmer circuit in the left half of the image. Pin 3 will start the triac up, activate it. From that point, it will always be on, like a closed switch, until the supply voltage is interrupted. The blue line shows the current flow, R is the lamp we want to dim.

We find triacs mainly in AC applications, for the simple reason that in DC applications we would need to pull the plug to the power supply to switch it off. With AC, this happens automatically each time there is a "zero crossing", when the voltage becomes zero. In the right half of the image, those zero crossings are marked "ZC".

What deactivates a triac is however not a lack of voltage, but a lack of current. Each triac has a minimum "holding current". If the current goes below that threshold, the triac switches off.

The higher the maximum current of a triac, the higher is also its holding current. A triac for 1.5kW will usually have a higher holding current than one for 500W.

And again our energy-consciousness is causing us unexpected trouble: LED bulbs do not consume much current. Imagine two 8W LED bulbs, which can these days replace two 60W incandescent bulbs. The incandescent bulbs consume more than 0.5A at 230V, while the LED bulbs may consume less than 80mA.

Now imagine you dim those two LED bulbs further down, soon you will have less than 10mA flowing through the triac. What happens? The triac can not detect enough current and shuts itself off. Then it may detect some more, because the capacitors in the bulbs had to be recharged, but that only lasts for a moment and it shuts off again. Again, we see flicker.

A few years back Philips had a special recommended list of dimmers on their website. If you looked through the list, you would find that all dimmers were very low power: 250W or even 125W. Why? Lower holding current.

Again, a solution for this problem would be to get rid of triac dimming for LED lighting and instead to control lights through an interface, as we do in our Regulus line, from 0.5-100%.
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Why dimmable LED bulbs often flicker

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

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 on the right part of the 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.
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Meet Pollux

Pollux is an A65 bulb (meaning it has a maximum diameter of 65mm). It not only looks different, it is different. Available in 12W and 15W, this bulb series achieves an efficacy of 100lm/W, which means that you will get 1500lm for the 15W it consumes. It also emits light at a wide angle of 270 degrees. And the key to all these achievements is its shape.

At whatever angle you install this bulb, its design will always allow air to flow behind the LED boards, where cooling is most needed. Even what you may think of as decoration serves as an air inlet or outlet. But don't worry, the openings do not create any "blind spots" (or rather dark spots), the bulb does indeed create a consistent light sphere.
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Same place, different color temperature, but same lights

In this image you can see two environments, one warm, one cold. Would you want to swap the color temperatures? Probably not. We are better concentrated at higher color temperatures, but lower color temperatures are more pleasant.

If you look closer, you will find that both photos were taken at the same location, even the camera position and angle are identical. Simply by changing the color temperature, the same location gives us a different feeling.

But here is the best bit: We did not even change the lights. What we did change was the command we gave our Regulus luminaires, to go to low color temperature for the first and to high color temperature for the second photo. The same Regulus luminaires could also emit light at any other color temperature between the upper and lower limit, not just two extremes.

We call this freedom. Our Regulus luminaires give you the freedom to choose not only what brightness you want where, but also what color temperature you want right now. Enjoy.
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