You need to understand clearly about Leading Edge and Trailing Edge in controlling light intensity with KNX

If you are looking to dim the lights in your home, shop or restaurant, you need to make sure that the bulbs and KNX dimmers you use are compatible, as not all dimmers are created equal. This article explains the differences between leading edge and trailing edge dimming and what to look out for to ensure compatibility and performance.

Understanding Leading Edge Dimming and Trailing Edge Dimming helps engineers choose the appropriate brightness adjustment method

There are two types of dimmers: Leading Edge and Trailing Edge, which are collectively known as phase-cut dimmers. These two types of phase-cut dimmers get their name from the portion of the AC wave that they cut.

Leading Edge Dimming

Leading Edge Dimming is a type of light dimming technology used primarily with incandescent and halogen bulbs . It works by clipping the leading edge (starting point) of the alternating current (AC) waveform to control the brightness of the light. This means that it interrupts the current as it begins during each half-cycle of the AC waveform. By clipping part of the waveform, the dimmer reduces the average voltage supplied to the bulb, resulting in dimmer light.

Leading Edge Dimming cuts off the first half of the AC wave cycle

Leading Edge Dimming is commonly used with incandescent and halogen lamps for the following reasons:

1. Compatibility: Leading Edge Dimming works on the principle of cutting the first phase of the AC voltage wave, which is a method that is fully compatible with the operating characteristics of incandescent and halogen lamps.

2. High efficiency:  Leading Edge Dimming is highly efficient in adjusting the brightness of incandescent and halogen lamps. This method allows for smooth brightness adjustment and causes less flicker.

3. Low Cost:  Compared with other dimming methods, Leading Edge Dimming has lower cost due to its simple structure and easy manufacturing.

4. High reliability: Leading Edge Dimming is a long-standing and highly reliable method. This method has few errors and a long life. 

Some limitations of Leading Edge Dimming:

1. Not compatible with LED lights:  Leading Edge Dimming can cause flickering at low light levels or a distinctive noise when used with LED lights. Therefore, this method is not recommended for use with LED lights.

2. Electromagnetic Interference:  Leading Edge Dimming may cause electromagnetic interference (EMI), affecting the operation of other electronic devices.

3. Energy loss:  Leading Edge Dimming can cause energy loss due to cutting the leading phase of the AC voltage wave.

4. Minimum wattage bulb requirement: Leading Edge Dimming often requires a minimum wattage bulb to operate, so this can be an issue with low wattage LEDs.

Leading Edge Dimming used to be the preferred method, but it is generally not recommended for modern lighting setups today, primarily for educational training purposes. If you are looking to dim LEDs or other newer technologies, trailing edge dimming or other compatible dimming methods are better options.

Trailing Edge Dimming

Trailing Edge Dimming  is a type of light dimming technology commonly used with modern dimmers, especially for LED bulbs . It works by clipping the trailing edge (the end) of the alternating current (AC) voltage waveform to control the brightness of the light.

Trailing Edge Dimming cuts off the second half of the AC wave cycle

Trailing Edge Dimming is commonly applied to LED lights for the following reasons:

1. Compatibility:  Trailing Edge Dimming works on the principle of cutting off the trailing edge of the AC voltage wave, which is compatible with the operating characteristics of LED lights.

2. Less electromagnetic interference:  Compared with leading edge dimming, Trailing Edge Dimming causes less electromagnetic interference, helping to protect other electronic devices to operate stably.

3. High efficiency:  Trailing Edge Dimming allows smooth brightness adjustment, less flicker and noise, providing a better lighting experience for users.

4. Long life:  Trailing Edge Dimming helps reduce wear and tear on LED lights, thereby increasing the lifespan of the lights.

5. Energy saving:  Trailing Edge Dimming saves energy more effectively than leading edge dimming because it does not cut the leading phase of the AC voltage wave.

With the above advantages, Trailing Edge Dimming is the preferred method of brightness adjustment for LED applications. However, dimmers using trailing edge dimming are often more expensive than dimmers using leading edge dimming.

Below is a comparison table between the two dimming methods:

Feature	Leading Edge Dimming	Trailing Edge Dimming
Cuts off	Leading edge of AC waveform	Trailing edge of AC waveform
Better for	Incandescent, halogen lamps	LEDs, low-voltage transformers
Cost	Cheaper	More expensive
Flickering	Can occur at low light levels	Less likely to flicker
EMI (electromagnetic interference)	Can generate	Less likely to generate
Minimum wattage requirements	May not be met with some bulbs	Generally not an issue

Conclusion

If you have to choose a dimmer to control the light intensity of your project, you need to consider the following factors:

• Choose a dimmer based on the type of light used (incandescent, halogen or LED).

• Consider cost and energy efficiency.

• Choose a dimmer that matches the LED type to avoid flickering.

You should also be sure to consult the lamp and dimmer manufacturer's instructions to ensure proper use.