Why some LED bulbs can be controlled with a dimmer and others not?

27.02.2013

How does LED work?

LED (Light-emitting diode) are an excellent source of low voltage light that requires little energy. However, they require a stable voltage source current (DC) in order to function effectively.

Individually, each LED requires 2-4 volts and according to its specifications, a few hundred mA. LEDs can be placed in series (in a light bulb or lamp, for example), which requires a higher voltage.

LEDs must be protected from fluctuations in voltages to prevent these fluctuations to cause a change in the intensity of the emitted light. Excessive current will produce increased brightness, but also a higher temperature and thus an accelerated deterioration of the LED.

Stable Current

To ensure a stable current, especially in applications with batteries where voltage fluctuations are constant, the majority of LED lighting is designed with a driver. Some drivers provide a constant voltage, while others maintain a constant current, protecting LEDs from overload, thus ensuring consistent performance and increased durability.

Attenuate your LED using a dimmer

An interesting feature of LEDs is that they can be attenuated using a dimmer. Take note: Not all bulbs or LED lights are compatible with dimmers. The main reason is that the function of dimmers is opposite to that of the drivers, namely to change the brightness of the LED.

The majority of dimmers operate on the principle of PWM (Pulse Width Modulation). In short, it's like turning on and off the LED very quickly at a high frequency, imperceptible to the naked eye, giving the impression that it illuminates less strongly.

In fact, it illuminates less at a time ... This method allows to maintain a steady voltage and current while varying the perceived brightness.

Here is an illustration of the basic principle of PWM power supply to 5V.

 

  • A cycle represents the time-space between the green bars.
  • At 25%, the power is only applied for ¼ cycle, which for an LED, gives the impression that it illuminates only ¼ of its maximum intensity. The same principle applies at all levels between 0 and 100%.
  • At 100%, the power is continuous, which connects the LED directly to the power source.

 

Some dimmers offer up to 256 levels of attenuation between 0 and 100%.

Different Results

Depending on the design of the 'driver' of the bulb or the lamp, it is possible that the result of the dimmer doesn’t live-up to expectations. In some cases, there may be an annoying flickering. In other cases, there is simply no variation or the change is not evenly distributed over the entire range of the dimmer. The results vary depending on several factors, including the bulb, dimmer and power supply voltage which varies constantly.

In general, smaller RVs bulbs and LED strips work well with dimmers. On the other hand. with fixtures, results will vary with different models. The best way to know is to try them in order to ensure their compatibility.

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