In this article Ivory Egg, suppliers of smart home solutions, lighting and lighting design services, discusses the benefits and pitfalls of modern lighting and the importance of a professional lighting design and control in the home.
Lighting used to be simple – a pendant in the middle of the room with a switch on the wall. If you were feeling adventurous, you may even have installed a dimmer. Now those days are long gone, with the Light Emitting Diode (LED) having created a far broader and deeper choice for domestic lighting than ever seen before.
As in the early days of low voltage halogen, there has been a steep learning curve and selection and placement of products is crucial to an effective lighting scheme, not to mention the need for competent controls.
Selection
Regardless of the manufacturer, the performance of the LED chips in any production batch will vary. To overcome this, LEDs are binned. This sorting process ultimately controls how closely matched the LEDs are and, if done correctly, adds to the cost of the LED. It will also result in a fair number of rejected chips, which are often sold on as low grade LEDs.
One of the most common performance issues relates to the colour temperature of the LED. This is normally expressed as ‘Warm White’ or ‘Cool White’ but the more accurate classification is Kelvins (K); a typical warm white LED will have a colour temperature of 2700K. This colour temperature has an accuracy rating which is measured in MacAdam Steps, which gives the amount of variation from the target temperature that can be expected. One MacAdam step means no visible variation, whereas a LED above four steps will have a visible difference. Quality luminaires use LEDs that are consistently less than two steps but, if you can’t find this data for a product, it’s likely to be four steps or above.
Another parameter that has a huge impact on the quality of light is the Colour Rendering Index (or CRI). This indicates how accurately colours appear under the light and is an important guide to how the interior and décor will look. The rule of thumb is: the higher the number the better. You should aim for around 85+ for non-demanding environments and 95+ for more critical applications, with the highest possible value at 100.
One of the driving forces behind LED lighting has been the green factor, but exactly how efficient is an LED?
The luminous efficacy is expressed in lumens per watt, but there are other factors to consider. The driver that forms part of the luminaire will also have losses; you should look for performance figures that quote lumens per circuit watt for a truer picture (drivers typically are up to 85% efficient). The optical loss is another factor as the luminaire will have mixing chambers, reflectors and lenses to shape and direct the light which will reduce the raw output from the LED. A reputable lighting manufacturer will state the delivered lumen output as well as the raw output but, if it’s not stated, it could indicate large losses.
Now we know what to look for with efficiency, what about life? The lumen output of a LED will depreciate over time; this is true of all light sources. While LEDs are solid state devices, deterioration can occur, causing considerably less light output long before the end of its service life. This is a big issue in poor quality LEDs, particularly if housed in a fitting that doesn’t provide sufficient air flow.
Most LEDs claim a life time such as 50,000 hours but a far more important guide is the Lumen Maintenance (L), which predicts usefulness of an LED over its life. Thankfully, there is a standard by which this Lumen Maintenance can be quantified. The most common is the L70 rating, which determines a lumen output reduction of no less than 70% of the initial output after 50,000 hours of use. As an example, a luminaire with a 1,000 lumen output will produce no less than 700 lumens after 50,000 hours. There are also L50, L80, and L90 ratings.
This is an important factor when you consider a fitting could be producing half of its original output long before it has stopped working, rendering it useless and in need of replacement. These parameters apply to all LEDs, so if finding the information is difficult you should wonder why.
It can be particularly difficult to get this information on GU10 LED replacement lamps as these are mass produced and can have minimal binning/quality control. Integrated luminaires with Chip on Board (COB) LEDs will generally offer better performance but in any case, the information should be checked.
Design
Lighting design is a mixture of art and science; understanding the physics of light and how a luminaire will produce light are important elements of the design process. This concept has brought new dimensions to rooms as the light itself can create depth, emphasis and drama in a room, all from a simple press of a button. There are numerous ways that lighting can achieve this, the design will need to consider lux levels, create depth and texture and provide feature or impact.
A great lighting design should enhance and lift the home and not just light it. It can take years of experience to be able to offer this level of design so consider using a lighting design service to ensure the lighting brings the home together.
In control
An important element of lighting design is the controls. The ability to control the light will literally shape the look and feel of the room and having all the downlights on one circuit and a couple of wall lights on another just won’t do it. Having more circuits will increase flexibility and give the ability to use the lighting creatively.
One solution is to use scene control, storing the light levels so they can be recalled from a single button. This simplifies the control of numerous circuits and is a must for any room with three or more circuits. This is the crux of the matter: to create the ambience a lighting design sets out to achieve, the lighting must be controlled in small, logical circuits with a simple user interface that can recall a predetermined scene.
Dimming
Whilst dimming LEDs is fraught with technical complexities, huge improvements have been made in recent years. However, dimming compatibility is more than just the absence of flickering or flashing lights, it also relates to the effective light output and controlled range. The perception is that a dimmable light should have a linear output from 0 to 100% but the reality is far from that, with the worst culprits being GU10 LED replacement lamps.
The two graphs (pictured above) show the difference in output (lux) between a high end GU10 and a COB downlight using a main brand driver. It is clear to see there is no linearity with the GU10 and a near linear output from the COB downlight. The GU10 also suffers from a lack of change at the top and bottom of the range with most of the dimming happening between 20 and 70%.
Both luminaires were dimmed with a KNX dimming actuator that was specifically designed to dim LED lights and has a proven track record of compatibility with a wide range of LEDs. Of course, results will vary with different dimmers or lights but it does illustrate that the label ‘dimmable’ doesn’t always guarantee what you’d expect.
