Category Archives: dimming

Million shades of white LED

Nowadays LEDs have great efficacy and lifetime. They produce more and more light with less power. I think that it’s less important to increase efficacy because we have already reached what the market demands. What else we need from the light than a lot of lumens? In this blog post, I’ll compare the differences between white LEDs.

We all know that LEDs are available in different color temperatures. For example, Citizen 6 generation’s LEDs are available from 2700K to 6500K. They are also available in different color rendering indexes. Color rendering index simply means how well a white light source can show, or render, colors compared to sunlight. We know that the color rendering index does not always tell the whole truth (You can read more from this blog post).

Nowadays we need a light source that has good efficacy and color rendering, and it doesn’t hurt if the light source can be customized to use in many different luminaires. We want light source that brings colors vivid and alive. Also, design interiors with relaxing atmosphere.

Let’s look into what else affects the quality of light than the color rendering index and color temperature.

White without greenish tone

IMAGE: Black line in the picture is B.B.L. Red circles indicate below B.B.L. LEDs.

In some projects, we want a light source that makes white look whiter. Some LEDs may turn white into light green. Traditional white LEDs’ color temperature chromaticity is on or very near B.B.L. (Black Body Locus). Citizen also produces below B.B.L. LEDs. Their color temperature is below the B.B.L. line. As you can see in the picture, above the line is greenish colors and below the line is reddish colors. Below B.B.L. LEDs make white look pure white and it also renders red colors better. This way we can create light that doesn’t have a greenish tint.

Below B.B.L. LEDs are very popular in shop lighting and everywhere where brisk atmosphere is needed.

Read more about the color temperature from this blog post.

More attractive display with high color contrast

The general color rendering index (CRI) is defined as an average of the sum of first eight R-values. However, these first eight indexes are rather less saturated colors, while indexes R9-R12 represent highly saturated colors. This means that the same CRI doesn’t mean same color rendering.

The Citizen’s Vivid LEDs make colors seem brighter with better color contrast. The spectrum of light has been designed to have as good as possible saturation. This way Vivid LEDs can render bold colors vividly. With better saturation, you can read easier for example newspaper under the Vivid LEDs.

Below you can see a picture where Vivid LEDs are compared. The higher the bar is, the better the color renders. The comparison is done to halogen bulb (0= halogen bulb performance).

Great use for Vivid LEDs are places where good color rendering and concentration is needed, for example, clothing and cosmetic stores, art galleries, schools, hospitals, and offices.

There are two different Vivid LEDs:

  • Brilliant Vivid – Very high color contrast.
  • Natural Vivid – High color contrast.

Vivid LEDs are meant to be combined. Use Brilliant Vivid as spotlights to bring color and textures up, and Natural Vivid as base light because it has better efficacy but has still very good color rendering and contrast.

Change the color temperature of light

Everyone is now talking about “human-centric” -lighting in the lighting industry. It means that by changing the color temperature you can maximize productivity and improve concentration or create comfortable atmospheric feeling. Citizen’s Tunable White is a great solution for “human-centric” -lighting. Its color temperature can be changed freely from 2700K to 6500K. This means that you can achieve warm light like incandescent lamp and daylight with only one module. In addition to changing the color temperature, you can also dim the brightness.

Early Tunable White products have been big sized modules. Citizen’s Tunable white is as small as the COB. This means that you can make a lot of smaller Tunable White luminaires than before. The small size also gives more even light. The spots between cool and warm dies are practically invisible, which guarantee more smoothly light.

By connecting Tunable White into the right control unit, you can change the color temperature and brightness according to the time of day.

Light that gets warmer by dimming

One of the features of the halogen lamp is that when dimmed its color temperature changes warm-toned. Citizen’s Dim-to-Warm COB-LED does the same thing.

Dim-to-Warm is a COB-LED, so you don’t need any complicated special features from the driver, like two-channeling or programming features. Ordinary triac dimmable driver is enough. Dim-to-Warm COB has preset dimming curve, so when you dim it, its color temperature changes automatically just like halogen.

I hope that this blog post gives you some new thoughts for designing the luminaires. When you use any of the LEDs that I just presented to you above, you’ll get a luminaire that has more to provide than just ordinary light source. This way you can have competitive advantage.

You can download presentation about Citizen LEDs below. If you have anything to ask, please do not hesitate to contact me. My email address is taru.matikainen@light.fi and I’m always happy to help you.

Download Here

Different Dimming Types for LED Lighting

You can use several different dimming options to dim LED Lighting. What are the possibilities and what dimming should you look from a LED driver? I’m going to answer these questions in this blog post by going through the different systems.

The goal is to give you the basic understanding of the dimming methods available at moment.

I am grouping the dimming methods in two main groups: analogue and digital.

When you want to control lighting, you have to know some basic issues of your lighting fixtures:

  • Are your fixtures dimmable? If yes, what is the dimming method which works together with your fixtures
  • If your fixtures are non-dimmable, then you can only have on/off – function.

Analogue

Analogue dimming covers all dimming systems that don’t transform the dimming signal into bits and controls the lighting in analogue manner.

Phase dimming

Phase dimming systems dim the lights by altering the supply voltage.

Leading & trailing edge dimming

Before LEDs, we used to dim halogen lamps with wall dimmers.  We can still use these kinds of dimmers.  But dimmer, driver and LED-module must be compatible with each other.

This type of control is accomplished without any need for an additional control wire. It involves connecting a dimmer in series between one of the mains wire and the equipment.

The dimmer cuts part of the mains voltage sinusoidal waveform to a greater or lesser extent in order to dim luminous flux even from 1% to 100%  (this value depends on dimmer and driver).

Depending on how the driver makes the mains voltage cut, it is possible to distinguish between two types of dimming:

Leading-edge dimming

Leading-edge dimming

Trailing edge dimming

Trailing edge dimming

Leading-edge dimming:

Dimming cut-off in the wave on its ascending side, from the beginning (phase cut-off at ignition). This is traditionally used in halogen lamps supplied through electromagnetic transformers.

Trailing-edge dimming:

Dimming by cut-off in the wave on its descending side, from the end cutting backwards (phase cut-off at switch off).  And this way of dimming causes less interferences than leading-edge dimming.

There are dimmers and equipment that support both types of dimming, and others that support only one type.

Leading & Trailing-edge dimming LC

Leading & Trailing-edge dimming LC

Leading-edge dimming L

Leading-edge dimming L

Trailing-edge dimming  C

Trailing-edge dimming  C

1-10V regulation

The 1-10V system enables dimming of the luminous flux from around 1…10% to 100%. This is done by sending an analogue signal to the equipment over an additional, two-wire control line. These control wires have positive and negative polarities respectively and that must be kept in mind when wiring up the system.

The analogue signal has a direct voltage value of 1V to 10V. 1V or short-circuiting the fixture’s input control gives the minimum light level. While 10V or leaving the input control circuit open gives out the maximum light level.

International standard, IEC 60929, defines the regulation curve. The regulation curve represents the relationship between the control line voltage and the luminous flux. It reflects a practically linear relationship in the range of 3V to 10V.

To get a response adapted to that of the human eye it is possible to use logarithmically controlled potentiometers.

Regulation curve by IEC 60929

Regulation curve by IEC 60929

These in light fixtures generate power control with 1-10V dimming.  Driver supplies a current to the controller through equipment control terminals. The controller current must be from 10µA to 2mA. The maximum control line current is obtained with a voltage of 1V and the minimum with a voltage of 10V.

This dimming system is unidirectional, i.e. the information flows in one direction, from the controller to the light fixture. The latter generates no feedback to control. This means that this system can’t be controlled by a software. Groups have to be created by wiring. This system can be integrated into building control systems.

The voltage drop in the control line wiring limits its length. Therefore, the maximum distance is limited by the number of control gears connected. The latter establishes the current per line and the cable diameter used.

Touch Control Push Button  (analogue but can be connected to digital systems)

Touch Control is a system that enables the simple and economic dimming of luminous flux. It uses the mains voltage as a control signal, applying it with a standard push button on a control line, without any need for specific controllers.
The Touch Control system enables you to carry out the basic functions of a regulation system with a power-free pushbutton. Depending on how long the button is pressed it is possible to switch the light on or off or dim it. Switching the light on or off is done by short, sharp pressing or “click”. If the button is pressed for a long time it is possible to dim the luminous flux between the maximum and minimum levels alternately.

Touch Dimming

Touch Dimming

This is a unidirectional interface, i.e. information flows in one direction. The equipment does not generate any type of feedback, so it can’t be controlled with a software. Groups have to be created by wiring. This system cannot be integrated into building control systems.

The length of the wiring and the number of equipment that can be connected, are theoretically unlimited. But in, asynchronism may occur during switching on and dimming, at distances longer than 25 meters, and with a larger number of fixtures connected.
Owing to its characteristics, the use of this dimming method is recommended for individual offices, small meeting rooms or bedrooms, landings and small spaces in general.

Digital

Digital dimming covers all dimming systems that transform the dimming signal into bits and controls the lighting in digital format.

DALI Regulation (digital)

As revealed by the meaning of its acronym, Digital Addressable Lighting Interface, DALI is a digital and addressable communication interface for lighting systems.

This is an international standard system in accordance with IEC 62386, which ensures compatibility and interchangeabil­ity between different manufacturers’ equipment marked with the following logo: DALI controller

DALI-logo

DALI-logo

It is a bi-directional dimming interface with a master-slave structure. The information flows from a controller, which operates as the master, to the control gears that only operate as slaves. The latter carries out the orders or responds to the information requests received.

Digital signals are transmitted over a bus or two-wire control wire. These control wires can be negatively and positively polarized, though the majority control gears are designed polarity free to make connection indifferent.

DALI Dimming

DALI Dimming

You don’t need especially shielded cables. It is possible to wire the power line and DALI bus together with a standard five-wire cable.

Unlike other systems, you don’t need to create wiring groups. Therefore all the pieces of fixtures are connected in parallel to the bus. Without bearing in mind the grouping of these, simply avoiding a closed ring or loop topology.

You don’t require mechanical relays to switch the lighting on or off, given that this is done orders sent along the control line. You don’t need are bus termination resistors either.

Consequently, the DALI interfaces offer wiring simplicity in addition to great flexibility when it comes to designing the lighting installation.

The maximum voltage drop along the control line must not exceed 2V with the maximum bus current of 250mA. Therefore, the maximum wiring distance allowed depends on the cable cross-section, but it must never exceed 300m in any case.

Configuring

After wiring, the DALI lighting system is configured with the software. You can create up to 16 different scenarios, addressing the equipment individually up to a maximum of 64 addresses.  This can be made with groups up to a maximum of 16, or simultaneously by means of a “broadcast” order. You can change the configuration at any time without any need for re-wiring.

The DALI system has a logarithmic regulation curve adjusted to human eye sensitivity, defined in the international standard, IEC 62386. The possible regulation range is set at from 0.1% to 100%. The driver manufacturer determines the minimum.

DALI Regulation Curve by IEC 62386

DALI Regulation Curve by IEC 62386

With the software, you can change the “fade rate”. “Fade rate”is the time needed to go from one light level to another(fade time) and the speed of the change.

The DALI system lies in the fringe between the complex and costly but powerful ones; control systems for buildings that offer total functionality and the most simple and econom­ic regulation systems, for example, the 1-10V one.

You can use this interface in simple applications indepen­dently, to control a luminaire or a small room. You can also use it in high-level applications such as being integrated by gateways into building smart control systems.

These are the most common systems you can use to dim LED. There are a lot of different dimming systems for different driver manufacturers. I can’t cover all of those in a single blog post. I will be writing a different post about wireless dimming options.

If you have anything you would like to know, you can always contact me.

Sources: ELT