How to choose stable LED installations

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LED lighting is consistently increasing in popularity as it is being installed as an alternative to traditional fluorescent and halogen light sources. However, when installing a LED light, there are a few precautions that need to be kept in mind.

Few years ago, there were not many LED manufacturers on the market. This made the lighting market more unstable as there were very few options for energy saving lights. But in present time, there are several options of lighting that runs on LED technology and save both maintenance and energy. These LED lights live up to the expectations of the end user. Also, there are many new inventions in the LED industry that have increased the lamps’ efficiency and reliability. It is believed that the luminous efficacy and quality of LED doubles every three years.
However, looking at the other side, there are still lighting concepts that use LED-based solutions that have flaws in them like glare. 

Color stability in professional installations

There are few terms and concepts that are associated with LED-based products and should be known by every consumer using LED. Color stability is one of them. It plays an important role in LED-technology and output. High color stability can be ensured by allowing LED a large color temperature.

SDCM (Standard Deviation Color Matching) or MacAdam Color Steps is a term associated with LEDs that indicates the tolerance level where the human eye cannot perceive fluctuation.
SDCM defines the tolerance in the color temperature with a number. The lower the number, the smaller the tolerance with respect to the XY color space. SDCM can also avoid that the human eye potentially can detect any variations in the white color of light from a given light source.
In offices and corridors, we typically use 4-7 SDCM. In such places, we may see a difference in the white light source color if light is falling on a white wall. In large rooms, the difference is very hard to see. Lamps placed near a white wall require 2-3 SDCM. A wall washing requires around 2 SDCM. Selecting 2-3 SDCM or even 2 SDCM can easily cause increase in expenses on final fixture. Figure 1 shows how different steps are used at different color temperatures. SDCM should always be written in a description of a lighting fixture.

Figure 1 shows that it is important to look at MacAdam Color Steps. Here are the different ellipses from different color temperatures. The eclipse becomes smaller as we move down the color temperature. 


LED lifespan

Just like the color stability of an LED, there are various other standards that one needs to be aware of before using LED. The standard IESNA LM 80 and IESNA LM 79 illustrate lumen degradation or weakening and flux skills over time. In other words, here is an example of how much light is sent out of the light source for a given period of time. This is called LED lifespan. It is always important to know how to measure LED lifetime.
LEDs luminous flux reduces over their lifetime. The life span of LED that is typically designated by the term L70 and a figure that should be read indicates that the luminous flux has dropped by 30 percent after the given lifetime.
B10 and B50 are theories that highlight the failure rate as a percentage, which is expected within the given lifetime. In professional lighting systems, there is a requirement for a lifetime of min 50K L70 (B10) hours.

 Figure 2 shows how lumen degradation can occur in an LED-based luminaire.

Fig. 2 The figure also shows Lumen degradation for NS60 where the fixture is stressed with air temperature of 55 degrees C.

Energy efficiency

The long-life and high energy efficiency is the reason for great popularity of LED in all forms of developments including commercial and residential sectors. Today, the LED we see on the market comes with an efficiency of 161 LPW (lumens per Watt). This amount is more effective than any other light source on the market. LED-based luminaires and retrofit lamps, however, have a lower efficiency due to loss of driver, thermal parts (cooling coils) and reflectors or lenses used to spread the light.

Before opting for LEDs with highest energy efficiency, a consumer should always assess the environment in which the fixture is to be used. The high lumen packages can be combined with optics and reflectors, creating unpleasant lighting. Furthermore, when using very efficient luminaires, there are various problems associated with the maintenance of a sufficient regularity of the light.
Hence, high-energy efficient LEDs are not always considered as the most efficient luminaires. The medium in which light from the LED is transported to the room also plays a significant role in creating a successful lighting system. The most effective LED-based luminaires are typically on 90 to 150 LPW including the loss of the previously mentioned components. In comparison, highly efficient T5 fluorescent comes with 70-80 LPW including the loss of reflector and the coil. 


How to write luminaire definitions

After explaining different factors related to LED lighting, we will now explain the luminaire definitions.
The description can be divided into two categories depending on the form of tendering: 

  • General descriptions 
  • More specific descriptions.

The general description of the lighting system is often found in projects including high energy efficiency or the prospective plant maintenance. These could also be used in EU tenders, where there are rules about whether luminaires may concretize. Using these, many construction projects might face financial pressure and hence cheapest lighting solutions deem necessary. Many contractors try to find fixtures that meet the general description. 

So, let us give you an example on how to write a luminaire definition: 
Round luminaire for ceiling mounted installation, diameter ØXXXmm. Polished reflector, white frame, light source type (eg. 1xTC-DEL 26W) comes with dimmable ballasts, lighting in the room set up as evenly distributed illumination providing min. 200 lux.
In addition to describing the system, the definition should meet Danish standards (eg. DS700). With the boom of technology relating to new LED-based lighting fixtures, it is also possible to make a more detailed description.

A specific description could look like this:
Type fixture (eg. Downlight), LED light source min. X.XXX lm (lumens), viewing angle (eg. 60 degrees), receiving maximum power XX W (Watt), Ra / CRI color rendering min. Raxx (eg. 80Ra), X.XXX Kelvin color temperature (eg. 3000K), the color stability SDCM (eg. 2, 3, 4, 5, etc.), Life in hours XX.XXX (eg. L70 B10), description of the shield / reflector, control principle (possibly. DALI or analog to dim and control the light otherwise), leakage current (eg. Maximum 0,025mA) supply unit including driver / coil if necessary + dimensions on this, painted in RALXXXX installed mechanically with screws for example, protection for the product IPXX, terminals for supplying or X connector mounted on the power cord. Dimensions or a line drawing can also be an option to include in the description.

Similarly, there are advantages in describing luminaire construction material (e.g. Aluminum or Stainless steel parts). In relation to the latter, a principle drawing of the lighting concept is displayed. All these extra descriptions put barriers for other fixtures that might cause problems in the project.