What you should know about LEDs

If you plan to use LED lights with dimmers you should buy carefully, as not every product is suitable for every project. Five questions will help you to choose the best technology.

Please note that the following questions and information are only meant as a supporting guideline which might help you with the general decision for or against LEDs. If you wish to weigh the details of dimming performance and installation costs, please refer to the websites and brochures of the respective producers or contact us directly via mail@illutrade.com.

 

1. Which dimming range should the lamp offer?

Every light bulb can be dimmed to a light intensity of less than one percent of visible light – so dark, that the orange glowing wire is visible to the naked eye. LED lamps, however, reach different light intensities. One product might for example be dimmable to 50 percent of visible light, another to 10 percent. That is why not every LED is suitable for every area of application. LEDs, which are only dimmable to 50 percent for example, will hardly be fitting for a media room.

When choosing a product you should be aware that most LED manufacturers do not indicate the dimming range of their lights and lamps in strengths of perceived light but in strengths of measured light. The difference between the two: The human eye perceives light usually as brighter than a gauge (the reason being that the pupil widens in dim lighting to let in more light). As a result, we perceive the lamp brighter than the information on the packing might suggest. A measured luminosity of 20 percent corresponds for example to a perceived light intensity of 45 percent.

If you want to avoid buying LEDs with too bright a dimming range, you can use the following formula. The perceived light intensity of a lamp equals the square root of measured luminosity (as in the example above: √0.2 = 0.45).

2. With which dimmer should the LED be used?

The answer to that question should be one of the following options, because these include the most common protocols on the market. Some of these protocols have been used for decades and/or are based on tried and tested industry standards. Using them should support the safe performance of LEDs in line with expectations.

Light bulb or leading edge phase-cut dimmers are usually used with light bulbs and low voltage lamps and represent the most common control system worldwide: Globally, more than 100 million units have been installed. Anybody who wants to replace other lights with LEDs, usually has to deal with this kind of dimmers. Leading edge dimmers have the benefit of not necessitating an earth cable in the switch box. A disadvantage is, however, that they only allow precise and flicker-free dimming of most LED lamps under certain conditions.

Trailing edge phase-cut dimmers usually control low voltage halogen lamps with electronic transformers. They are suitable particularly for controlling capacitive loads as generated by LED drivers and therefore support flicker-free dimming of LEDs. The only disadvantage of these systems: They are not nearly as common as leading edge dimmers.

Internationally, analogous 2- or 3-wire dimmers are primarily used for controlling fluorescent lamps, mostly in larger commercial areas and office buildings, where high fluorescent loads need to be managed. These dimmers are also relatively widespread as they are installed in around 2 million circuits worldwide.

0 -10 volt control systems are based on a tried and tested industrial standard for electronic ballasts (IEC 60929). To date, they are primarily used in energy management systems, e. g. in connection with motion and daylight sensors, but they are also suitable for controlling LEDs. As the 0-10 volt controllers are insulated from live cables, they can be touched and wired without danger. Buyers should pay special attention to the packaging when purchasing these controllers, since not all 0-10 volt systems on the market are compatible with IEC standards.

DALI-controllable electronic ballasts are named after the standard they meet: The “digital addressable lighting interface” protocol was originally developed in Europe, but is nowadays widespread also in other regions. As it allows for the digital controlling and therefore for very precise adjustment of single light fixtures, it is mainly used in commercials buildings.

DMX control systems support the “digital multiplex” protocol, which is used primarily in stage and event technology. It is suitable for controlling and dimming RGB LED applications, as these usually profit from a high speed and a high number of channels.

3. Do light fixtures and dimmers allow for continuous dimming? Will they light the room without flickering?

Each manufacturer has its own definition of “dimming” and not every definition corresponds to the clients' expectations. Most of us think of dimming as the continuous adjustment of light intensity, such as we know it from “dimmable” light bulbs. We are used to the corresponding changes an adjustment of the switch (usually by turning it) causes in the lighting of the room. Incremental, “choppy” changes in light intensity contradict our previous experience. As a consequence, dimmer and LED lamps should interact in a way that does not cause perceivable “jumps” in luminosity. Moreover, they should provide flicker-free lighting of the room at any time and at any light intensity, i. e. without any unexpected modulation of the brightness. Disturbing flickering can be caused by “interferences” in the power supply line, by “noise” inside the dimmer, by imperfect tolerance settings of certain circuit components or by an insufficient circuit layout in the LED driver. However, good products should be robust enough to allow flicker-free dimming despite all these potential interference factors.

4. What is the minimum/maximum number of lights that can be connected to a dimmer?

Electricians know that this is not an easy question to answer. It is not enough to divide the 600 watt power of a dimmer by the 10 watt power consumption of an LED and conclude that the dimmer circuit allows for a maximum of 60 lamps, because the indicated power consumption is just an average value. It is possible that the real power consumption of a 10 watt LED temporarily surpasses the 10 watt mark during a half cycle (inrush current). Disregarding this fact can lead to overloading the dimmer system and cause permanent damage.

Calculating the minimum number of lights per dimmer can be necessary, since many light bulb dimmers need a minimum load to function properly. This minimum load lies mostly between 24 and 60 watts – a value which could usually already be reached by using a single light bulb. When using LEDs it might therefore be necessary to install at least three or four light fixtures for the dimmer to work properly.

5. Has the LED product been tested with dimmers of different manufacturers?

The last and maybe most important question potential buyers should ask: Which tests does the manufacturer of a certain product run? Has the LED light fixture been tested with different dimmers from different manufacturers? Have the dimmers been tested for flickering? Has the manufacturer conducted these tests alone or in cooperation with the producers of the dimmers? How reliable are these tests? If a manufacturer can not or only insufficiently answer these questions, it is usually advisable to choose a different product.

Conclusion

If you ask the aforementioned questions before buying dimmers, light fixtures and LED products, you should be able to avoid all performance and compatibility issues mentioned at the beginning, while profiting from an energy-efficient, dimmable LED lighting and without having to compromise on light and performance.

Author: Jan Ewald, Sales Manager Germany and Marine, Lutron Electronics GmbH

You can find more comprehensive information about specific dimmers or LED lamps and their technical specifications, compatibility as well as installation and operational costs under the following link:

http://www.lutron.com/en-US/Service-Support/Pages/Technical/Design-SelectionTools/LEDDimmerMatrix.aspx

On the 1^st September, 2016 the ban of the European Commission on inefficient halogen lamps with directional light output went into effect. A great number of lighting systems relies on lamps with a GU10 fitting. In order to keep using these systems it would be sensible to equip them with LED lights. But that is easier said than done! Simple and inexpensive LEDs, so-called “retrofit lamps”, are susceptible to current and voltage fluctuations, which is evidenced by flickering, irregular light colours and different behaviour when switching on or off the light. These effects are especially pronounced when dimming the light intensity. The reason: Each LED chip reacts slightly different due to the electronic wiring.

With respect to conventional light bulbs, using lamps from different manufacturers was no problem. After changing the lamp, the buyer could expect the light fixture work just as it did before. This, however, is not the case when using LEDs. Special attention has to be paid to the compatibility of all components of the lighting system: the lamps and the dimmer, or better said, the control mechanism and drivers which power the LED lights. But don't worry! These challenges can be overcome if you bear the following tips in mind:

1. Note that ALL LED systems have a driver (transformer): This electronic component converts the 240 V alternating current into low voltage continuous current needed by the LED chips. Separate LED drivers with a range of 12-48 V have become the norm. Each LED system can be designed for a different voltage or a specific current. In dimmable retrofit lamps working with 240 V the drivers are “hidden” inside the lamp, e. g. inside the base or on a board, which is integrated into the reflector or the casing. In bigger, professional overhead light fixtures a separate box containing a so-called LED driver is used, which is wired to the actual lighting system. The compatibility of drivers and control mechanisms (digital DALI or dimmer) are the most important components of every LED project in order to achieve smooth dimming without any disturbing flickering.

2. Not all LED lamps are the same: Let's first have a look at LED lamps without separate driver. Different LEDs might also behave quite differently, even when connected to the same dimmer. The same is true for different batches from the same manufacturer. Even if such retrofit lamps look the same on the outside, they can exhibit considerable differences when combined with a standard dimmer. Furthermore, some LED lamps are generally unsuitable for dimming. This information is often overlooked because it is sometimes hidden in the small print on the packaging. It is also important to use only tested lamps which have proven that they function with a certain dimmer. However, the risk remains that the lamps flicker or blink, especially in the low control range of 20% or less, and that they turn off at different times.

3. Mind the minimum load: Many older dimmers need a minimum load of 20-40 watt to guarantee failure-free operation. Newer models, which have been designed specifically for the use of LEDs, do not have these limitations. LED lamps might also work with older dimmers, depending on their design. In order to find that out without a doubt it is necessary to test the combination of lamp and dimmer. Some manufacturers also offer online lists with tested combinations. Development in the LED space is however very fast, so many test are already outdated when they are published, as the next batch or generation of LEDs is already on the shelves.

4. Use dimmers with “Low End Trim”: High-quality dimmers feature the control option “low end trim”. This refers to the lowest brightness at which the lamp is turning on. If the lamps flicker in the lower brightness range, this feature can prevent them from getting into an unstable state, i. e. there is no disturbing flickering.

5. Note that the lowest brightness level can differ quite strongly from lamp to lamp: Some lamps can be dimmed to a lower level than others. To describe this level, the measured performance is used, which is given for example as 1%, 5% or 10%. However, measured brightness and perceived brightness are two different things, because the pupils widen in dim light so that more light reaches the retina. In dim lighting we therefore perceive small changes in brightness more strongly than in very bright lighting.

This phenomena should be taken into account when choosing the lamp and the dimmer. In the eyes of the observer a lamp dimmed to 10% of measured performance has for example a brightness of 30%. To achieve a perceived brightness of 10%, a combination of lamp and dimmer is necessary that allows for the measured light to be dimmed to 1%. Far from all retrofit LEDs fulfil this requirement. For that reason Lutron Electronis lists the lowest measured as well as the lowest perceived brightness that can be achieved for all tested lamps in the company's LED Report Cards.

6. Verify for which kind of dimmer an LED lamp is suitable – leading edge or trailing edge phase cut dimmers: Some advanced dimmers are universal and offer both technologies in one device. This has the benefit that there is a bigger number of compatible lamps to choose from. Which of these two options is the most advantageous can only be determined through tests. Also note, that testing only one lamp is usually not enough. To get reliable information on the interaction of the components, several lamps should be used, e. g. 5-10.

7. Take into account the inrush current: In lamps that are dimmed with the leading edge method, high inrush current peaks can occur, especially when turning on the light. A 50-100 times higher current might damage electronic components inside the dimmer as well as inside the lamps. The intensity of the inrush current also determines how many lamps can be connected to a single dimmer. To find out how many LED lights can be controlled though one dimmer, the data sheet of the manufacturer should be on hand. The maximum number of lamps might vary strongly, depending on model and manufacturer. Sometimes a dimmer can be connected to twice as many lamps of a certain type compared to another type. If no specifications are available, the light bulb performance of a dimmer can, as a rule of thumb, be divided by 10 to determine its performance in connection with LEDs. For example, a 450 watt dimmer for light bulbs corresponds to LEDs with a power of 45 Watt.

8. DALI! Dimming the line voltage is not the only way to reduce brightness: Controlling the luminosity through voltage is the only option when using retrofit lamps and entails certain limitations, especially when dimming the light. However, there are other types of LED drivers that do not use 240 V phase dimmers.

LED drivers controlled by analogous or digital signals through separate lines are used for optimal, 100% flicker-free dimming and simultaneous turning on and off of any number of LEDs. The desired output brightness is then best transmitted digitally to the driver (transformer and control module or combined device).

These signals use protocols like DALI (Digital Addressable Lighting Interface) or DMX (Digital Multiplex) while 0-10 V is also still common. Especially in a professional environment or for commercial installations it makes sense to use digital control systems to guarantee high quality and longevity of the system. In their simplest form, the control devices can look like standard touch dimmers on the wall. Usually the control devices are integrated into the power distribution and are operated through differently designed switches in the room, remote controls, iPhone or Android apps or a central control software on a computer.

For the simplest form, like the DALI protocol, two additional control wires need to be included in the normal power cable. An electrician would than speak of a 5-core supply cable towards the lamp, e. g. NYM 1,5 mm² (phase, neutral wire, earth wire, DALI, DALI).

9. Why dimming LEDs at all? There are two answers to that. First, dimming reduces energy and therefore temperature at the barrier layer of an LED chip. That in turn prolongs the life cycle of an LED, i. e. the lamps need to be replaced less often. Second, dimming the lighting with the right combination of lighting control and lamps can create a pleasant feel-good ambience, which is usually the main reason. More or less as a side effect these lighting systems also use less power and help save money.

10. Consult test results: Since 2009 a team of highly qualified engineers of Lutron is testing which LED lights and dimmers are compatible. To date, mote than 2.000 different combinations have been tested. The results are freely available on Lutron's website: www.lutron.com/LED. The LED Report Cards of the lamps which successfully passed the test contain important information, for example how many lamps can be placed in each dimmer zone, what minimum and maximum output power is possible as well as the lowest possible brightness level as perceived by the human eye. Our customers increasingly refer to these LED Report Cards, as they guarantee finding a suitable combination of LED lamps and dimmer that does not cause annoying flickering.

Author: Jan Ewald, Sales Manager Germany and Marine, Lutron Electronics GmbH