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Rethinking lighting specifications

 

LED technology changes the way we interpret lighting metrics

In recent years, LED lighting has evolved from being a viable technology to one that enjoys mass adoption. As a result, it has replaced conventional lighting in a wide range of applications, from traffic highways to fashion stores. As this evolution continues, LED technology has moved on. It now enables innovative features that create new experiences of light. LED technology has also rewritten the rules for measuring and specifying light characteristics. Designing with LEDs is not as straightforward as it used to be with conventional technologies. For lighting designers to fully capitalize on the possibilities LED lighting offers, they must change the way they think about lighting and develop a new understanding of the relationship between commonly used light parameters, like CCT and CRI.

Short recap on the key light specifications

In order to create desired lighting effects, lighting designers need to be familiar with the different characteristics that express the color of white light. Correlated Color Temperature (CCT) is used to indicate the color appearance (or tint) of white light. CCT values indicate the apparent warmth or coolness of a light source. Lighting with a CCT value between 2700 K and 3000 K emits more energy at the red end of the spectrum and therefore appears somewhat reddish, which is associated with warmth. On the other hand, lighting with a CCT value of 4000 K and above, emits more energy at the blue end of the spectrum and hence appears more bluish, which is associated with coolness. However, CCT alone does not fully define white appearance since two light sources with the same CCT value can have very different visual appearances. That’s because the exact position of the chromaticity coordinates also contributes to the perception of whiteness.

 

Color Rendering Index (CRI) is a fidelity index that indicates how close, on average, the colors of objects appear when illuminated by a test source in comparison to a reference illuminant. CRI 100 is the maximum value, meaning that the light in question is as close as possible to the reference light source. Lower CRI values indicate that some colors may appear different in comparison to the reference illuminant.

 

Another index that is currently being standardized within CIE, and is closely related to CRI, is the Color Gamut Index (CGI). The colors of an object illuminated by a light source with a high CGI (CGI > 100) will appear, on average, more saturated, whereas the colors of an object illuminated with a lower CGI light source (CGI < 100) will appear, on average, less saturated. Whereas CRI only indicates there is a difference in color appearance between the test source and the reference illuminant, CGI indicates the direction of the difference: more or less saturation.

Limits of traditional lighting

 

In traditional lighting technologies, these aspects have relatively fixed relationships between them. For example, you can only increase saturation (CGI) when you decrease the fidelity (CRI). As a result, different light sources produce characteristic effects that have been suitable for certain applications. Halogen lamps were used in homes, car headlamps and stage lighting. HID lamps were used in TV and filmmaking, street lighting and shop lighting. These characteristics have led to certain misconceptions about the lighting metrics that were used to describe the whiteness and color of the light source. To describe the visual effect of light sources, light aspects like CCT and CRI are not the ultimate truth. In the past, the technology used (like halogen, CDM, CFL, etc.) influenced the perception of light quality significantly as certain metrics that were not commonly used were defined by the technology. For example, a halogen source and a CDM source can both have a similar CCT and a CRI > 90 but the light effect itself is completely different. In addition, it is often believed that higher CRI yields better quality light sources, whereas several perception studies have demonstrated that light sources with a CRI of 70 can be preferred over light sources with a CRI of 100. But this also depends on other characteristics that are not captured by CRI, such as color saturation.

LED has changed the game

 

With the advent of LED lighting technology all this has changed. It’s now possible to tune and optimize the light spectrum to meet specific characteristics. LED technology therefore makes it possible to create completely new lighting effects, designed in a way that optimizes the balance between the application needs and energy efficiency.

 

This allows lighting designers to create new lighting experiences. Since our perception of an object’s color depends on the spectrum of the light reflected off it, lighting professionals can not only influence the perception of the object, they can also affect the emotional response to it and its perceived value. This can be particularly valuable in fashion and food retailing, where quality of light and energy efficiency are key for stores. 

Bringing out the best in fabrics

 

Using this expanded functionality, Philips Lighting’s crisp white LED technology has been specially developed for fashion applications where perception of intense colors and whites is crucial. crisp white illuminates fabrics to bring out the best in both colors and whites using a single light source. Colors appear rich and intense while whites appear bright and crisp. This high-quality solution avoids the trade-off between color vibrancy and white intensity that is often encountered with traditional lighting technologies.

 

Solutions like premium white and premium color offer the best light quality possible without sacrificing energy efficiency in applications where both quality of light and total cost of ownership are important. By applying knowledge about lighting metrics in commodity technology and understanding end user needs, the resulting light sources offer great benefits in terms of customer experience, energy efficiency and creating the correct brand atmosphere in-store.

Ensuring long-term success

 

These are just some of the possibilities offered by LED technology as it completely rewrites the old rules and opens up a new world of opportunities to lighting design. To create high-quality light that produces the desired effects, lighting designers need to understand how the different light metrics interact with one another and use the right components. By creating new and vibrant lighting effects, they can attract and engage customers and achieve long-term success.