Circadian Lighting, Lighting Controls

Explainer: DALI-2 certification for tunable white lighting

Four pictures of the same office with lighting of different colour temperatures
Tunable white lighting is becoming popular in offices and other applications This is where the colour appearance – known as the colour temperature – is usually varied throughout the day, starting off warm before becoming cooler in the late morning and afternoon, and then becoming warmer in the evening.

What’s tunable white lighting? 

Tunable white lighting is one of the biggest trends in commercial lighting at the moment. This is a method of changing the colour appearance of the light in terms of how ‘cool’ or ‘warm’ it looks. 

This appearance – known as the colour temperature – is usually varied throughout the day, starting off warm before becoming cooler in the late morning and afternoon, and then becoming warmer in the evening. 

It’s becoming popular in applications such as offices, care homes, restaurants and hotels which want a more ‘natural’ type of lighting. 

How does it work?

Standard LED colour-mixing uses red, green and blue channels that are adjusted to deliver the entire range of the colour spectrum. Tunable-white  works in a similar way, using of a number of controllable channels to adjust the colour temperature of the luminaire’s white light output. The channels in a tunable-white system all produce white light, but with varying colour temperatures, from a warm tone to a cool tone.

Simple systems use two lines of LEDs, one warm white and the other cool white, which are cross-dimmed to change the colour temperature. One channel is usually a warm 2700K  (colour temperature is measured in Kelvin, K) while the other is a coolish 6000K. The more sophisticated systems, which deliver a better experience, use a range of LEDs.

Colour temperature is measured in Kelvin, K. Tunable white lighting systems tend to vary from between a warm 2700K to a cool 6000K.

What’s the best method?

The best tunable white installations are designed to replicate the familiar effect of dimming of a filament lamp, where two things happen at the same time. So as the light output is dimmed, the lighting warms up in the same way as a traditional tungsten filament lamp. In effect, the colour of the light follows the path of the idealised ‘black body curve’, a reference material that is heated up to very high temperatures until it radiates light. 

What are the main colour control techniques?

There are four main ways of control the colour output of light sources.

  • Tc (colour temperature)
    This is most popular way of controlling the colour so that it behaves like a filament lamp.
  • RGBWAF
    This allows simple control of up to six channels of colour such as red, green, blue, white, amber and a free colour
  • x-y coordinates
    This method tunes the output so that the colour corresponds as closely as possible to that shown in the figure for the point in the colour space defined by the x and y axis.
  • Primary N
    The primary N method gives direct control over the light intensity of each available output channel.

Where does DALI come in?

Dali-2 logo

DALI is by far the most common lighting control method for commercial applications in Europe. It’s field-proven and familiar to lighting professionals, specifiers and end users and there are thousands of DALI-compatible products on the market. So using DALI-2, the second-generation of the protocol, to control tunable white lighting makes a lot of sense. 

How can DALI-2 work with tunable white lighting?

The Digital Illumination Interface Alliance (DiiA), the global industry organization for DALI lighting control, has now expanded the scope of the DALI-2 certification programme to include tunable white colour control. 

Specifically, it has added the most common colour control method, Tc (colour temperature), as a feature for DALI-2 control gear such as LED drivers.

Lighting at the Kongsgardmoen School in Kongberg, Norway, uses tunable-white lighting throughout the school day

Who are the DiiA?

The DiiA is an open, global consortium of lighting companies that is growing the market for lighting-control solutions based on the internationally standardised DALI protocol. DiiA is driving the adoption of DALI-2, which includes more product types such as sensors and controllers; more features such as luminaire, energy and diagnostics data; clearer specifications; and increased testing.

How did the DiiA make this happen?

DALI-2 certification of LED drivers has been available since mid-2017. All DALI-2 drivers have compulsory attributes such as a standardised dimming curve. Tunable white colour control is now added to the list of optional features for LED drivers, which also includes the ability to store and report a rich set of luminaire, energy and diagnostics data (DiiA Parts 251-253 respectively).

What will be effects of this development?

‘DALI-2 certification for tunable white colour control has important implications for well-being and productivity in buildings,’ says Paul Drosihn, DiiA general manager. ‘For example, colour temperature control at different times of the day, coupled with light intensity measurements and occupancy detection from DALI-2 sensors, results in comfortable and efficient lighting schemes.’

Is any DALI-2 tunable white kit available now?

Yes, the first DALI-2 tunable white LED drivers from eldoLED, as well as drivers from other brands, are already listed in the online product database.

How can the DiiA be sure that kit from different suppliers will work together?

The DiiA has created a rigorous DALI-2 test procedure that allows its members to confirm that their products meet the requirements of Part 209 colour type Tc. The test results are verified by the DiiA as part of the DALI-2 certification process, building further confidence in the interoperability of certified DALI-2 products from different suppliers.

What about the other colour types?

The DiiA is working to develop DALI-2 tests for both the RGBWAF method (usually referred to as ‘RGB colour control’) and xy-coordinate (known as ‘xy colour control’). It’s intended that these colour types can be included in the DALI-2 certification program at a later date.

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