Why dimmers are different for normal and LED bulbs when both are connected to normal power?

Question

The title 😀

I would understand it for LED strips and so on, but if both bulbs are made for 230V (or whatever in US), why do they need different dimmers? Is there a difference in some dim range or something?

Thanks.

In: 14

Answer 1

LED light are not made for 230V, each element run on closer to 2.3V. So an LED bulb needs some way to reduce the voltage for the elements. But the main difference is that while traditional light bulbs have a very linear response to the voltage LED elements are almost purely on or off. The difference between fully on and fully off might be as low as 0.1V.

Traditional dimmers do not actually limit the voltage to the bulbs but rather turn the power off for parts of the cycle. If you dim the light to half strength the voltage is still 230V but the light bulb only get power 50% of the time. On very low settings you might notice a tiny flicker as the fillament cools a tiny bit between each cycle but not much. An LED on the other hand use so little power that even just the stray capacitance and inductance is enough to keep it powered for some time even after the dimmer cuts the power. So you need to turn the dimmer all the way down for it to have an effect at all. And then the LED will not just glow a bit darker but it will turn fully off and fully on for each cycle turning it into a strobe.

There are multiple ways of fixing this. Some LED light have electronic regulators in them and these can detect the precense of a traditional dimmer and regulate the light output to match. This is why you see some LED bulbs labeled as dimmable. The dimmers you see labeled as working with LED lights do not reduce the power by turning the power off for parts of the cycle, or even directly regulate the voltage down. Rather it limits the power in the circuit thorugh a variable capacitor. This allows it to regulate the power down to exactly the voltage where the LED turns off and will keep the voltage right in that narrow band. These do also work on traditional lights although the voltage band will be significantly greater.