The adoption of LED strip lighting for new installations is rising fast and there is an opportunity for further growth if the user experience can be optimised. LED strip lighting has captured the imagination of consumers, offering energy saving benefits whilecontrolling the mood or accent of any space.
Consumers are looking to increase the performance of strip lighting installations by changing the light intensity which, in turn, controls the mood of the space, allows easy switching between accents lighting and task lighting and increases the longevity of the LED’s. This is where a lack of information can lead to disappointing results.
Here are 5 things you must know about dimming LED’s to get the best results from strip lighting:
- What is analogue control?
The light intensity of any LED (the physical component) can be adjusted by simply varying the DC current through the LED component. This is called analogue control. This dimming method is very popular amongst typical GU10 type dimmable LED’s where the internal driver converts the RMS voltage from the dimmer into a corresponding constant DC current to the LED component, thereby achieving a linear dimming. However, since strip LED lights have a built-in voltage to current converter, external analogue control of the strip results in very poor dimming performance.
- What are the technological advantages of analogue DC current control?
- It is a mature technology which is ideally suited to 230VAC to DC current converters, especially where physical space is limited (such as in GU10 LED’s)
- Many circuit design choices and control IC’s are available and are cost effective, especially for 230VAC to DC current control application
- There is a quick response time to varying power supply conditions
- There is no high frequency flicker present if the current is a pure and constant DC
- What are the disadvantages of analogue control?
- It is costly to achieve very accurate control due to component tolerances
- Possible LED colour shift can occur
- It is difficult to achieve very deep dimming, especially when the LED characteristics can vary
- Due to these disadvantages, this control method is usually reserved for integrated type of LED lamps where the internal driver is matched to a specific LED component.
- What is Pulse Width Modulation or PWM?
To avoid the disadvantages of analogue control, most external LED drivers and some professional integrated drivers employ a digital dimming control. In most cases, Pulse Width Modulation or PWM is chosen due to the simplicity and maturity of PWM technology.
PWM control differs fundamentally from analogue control as it does not vary the DC level of the current. The output current of the driver is a fixed DC, matched to the LED’s nominal rating, but the current is turned off and on as is shown in Illustration 1. Thus, by reducing the “on” time, the average current to the LED reduces and it dims. However, disadvantages of PWM is that it is costlier to implement for typical “GU10” type lamps and there is a possible strobe effect especially in industrial applications where rotating machinery is used.
- What are the advantages of PWM?
- It is very accurate if the DC current is accurate
- There is typically no LED colour shift since the LED experiences only it’s nominal current
- Behaviour between manufacturing batches is very reliable and repeatable
- The technology integrates well with other digital technologies.
A major advantage of PWM digital dimming is that some traditionally “non-dimmable” LED lamps can be dimmed. For example, a typical 12VDC or 24VDC LED strip has an integrated voltage to current converter which allows it to be powered from a non-dimmable DC power supply. By simply wiring a bell-press digital dimmer or “DC dimmer” between the power supply and LED, as is shown in Illustration 2, the strip can be dimmed perfectly to a very low intensity, without any damage to the LED or power supply.