What's so great about "Ra97"? How lighting's color rendering can chang

When you see "Ra97" on the specifications of a lighting fixture, many people probably don't really understand what it means. "What is Ra?" "Can I really tell the difference between 80 and 97?" This time, we'll explain how this value affects our daily lives, along with scientific data.

Q: What does Ra stand for?

Ra (Color Rendering Index) is an international metric that indicates how naturally a light source displays the colors of objects. It scores how close the test light source is to a reference light source (sunlight or incandescent light), which is considered 100 points for color appearance.

Formally, it is the common index of CRI (Color Rendering Index) established by the CIE (International Commission on Illumination) in 1974, calculated as the average value of 8 test colors from R1 to R8.

In simple terms, the higher the Ra value, the more natural colors are reproduced, similar to how they appear under sunlight.

Q: Is there really a difference between Ra80 and Ra97?

Numerically, it's a 17-point difference, but the experiential difference is surprisingly significant.

A study published in the Journal of Asian Architecture and Building Engineering (2020) by a lighting research team at National Cheng Kung University in Taiwan found that when comparing LED lighting with Ra values below 80 and above 80, higher Ra values improved assessments of spatial preference, brightness perception, and liveliness.

Comparing specific daily scenarios:

Dining Table (Ra80 vs Ra97)
Under Ra80 lighting, the colors of meat and vegetables can look somewhat flat, losing their appetite-stimulating vibrancy. With Ra97, the reds, greens, and yellows of ingredients are clearly reproduced, making dishes look much more appetizing.

Children's Study Desk (Ra80 vs Ra97)
Accurately seeing the illustrations in textbooks and the colors of pens directly impacts learning efficiency. In an Ra97 light environment, color discrimination is easier, and eye strain is reduced.

Getting Ready/Makeup (Ra80 vs Ra97)
With Ra80, skin tone may appear duller than it is, and it's easier to misjudge foundation shades. Ra97 provides color reproduction closer to natural light, preventing "discrepancies" in color when you go outside.

Q: Is it enough to just look at Ra?

Actually, Ra has its limitations. The CIE Ra value is calculated as the average of only 8 colors, so even if some colors are extremely poor, they can be averaged out.

A particular problem is the reproducibility of R9 (vivid red). For general blue LED + yellow phosphor lighting, even if the Ra value is around 80, R9 can be negative. This means that red colors are not seen correctly. The complexion of skin, the freshness of meat, the color of red flowers—if R9 is low, all of these will appear dull.

This is where the new evaluation standard, IES TM-30, comes into play.

Q: What are Rf and Rg in IES TM-30?

TM-30, developed by the IES (Illuminating Engineering Society of North America), is a next-generation color evaluation standard that replaces Ra. It is also recommended by the U.S. Department of Energy (DOE) Technical Report and uses the following two metrics:

Rf (Fidelity Index)
While Ra evaluates 8 colors, Rf evaluates using 99 real-world color samples. On a scale of 0 to 100, 100 means a perfect match with the reference light. It can measure "color naturalness" much more precisely than Ra.

Rg (Gamut Index)
This index indicates whether colors appear "more vivid (>100)" or "duller (<100)" than their actual colors. 100 represents saturation equivalent to sunlight. Rg102 means slightly more vivid—that is, colors appear vibrant and natural.

According to DMF Lighting's explanation, even with the same Ra value, Rf and Rg can vary significantly depending on the light source. Therefore, combining TM-30 with Ra is essential to accurately assess light quality.

Q: What technology is required to achieve a high Ra value?

In the common "blue LED + yellow phosphor" method, a sharp peak around 450nm and a "valley" around 500nm are created in the spectrum. This discontinuous spectrum sacrifices the reproducibility of certain colors, making it difficult to consistently exceed Ra90.

In contrast, the violet chip + multi-phosphor method excites multiple types of phosphors simultaneously with a violet LED (around 405nm), generating a continuous spectrum across the entire visible light range. Recent papers published in the RSC (Royal Society of Chemistry) academic journal Inorganic Chemistry Frontiers (2022) and ScienceDirect report that the violet excitation method possesses high quantum efficiency (PLQY 95%) and excellent thermal stability, making it a suitable technology for achieving full-spectrum white light.

The significance of Ra97 achieved by lipro

lipro's ceiling lights adopt Violet Emitting Technology, achieving the following spectral performance:

Ra97—color rendering very close to sunlight with an 8-color average
Rf97—maintains equivalent fidelity even with 99-color evaluation
Rg102—slightly more vivid than sunlight, making colors appear vibrant

This means not only a high Ra value but also high quality according to TM-30 standards. In other words, it's not just about "making 8 colors look good," but about light that makes all colors appear natural.

A continuous spectrum with 94.86% similarity to sunlight across the entire visible light range of 425-650nm forms the basis of this high color rendering.

Summary: The truth behind "Changing the lighting changed the feel of the room"

“Even though I didn’t redecorate, the room suddenly felt brighter.” “The food started looking more delicious.” These are common comments from people who have switched to high-CRI lighting.

The reason is simple: colors that were previously unseen are now properly visible. In an Ra97 light environment, the subtle shades of the walls, the gradients of wood grain, the healthy complexion of skin—everything is reproduced in its true color.

When choosing lighting, don't just focus on "brightness" and "electricity costs"; also pay attention to "color reproduction". The quality of your life will begin to change with the quality of light.

References

CIE (1995). "Method of Measuring and Specifying Colour Rendering Properties of Light Sources." CIE 13.3
Chen, H.W. et al. (2020). "LED lighting system for better color rendition space: the effect of CRI." Journal of Asian Architecture and Building Engineering
IES (2020). "ANSI/IES TM-30-20: Method for Evaluating Light Source Color Rendition."
U.S. DOE (2022). "Background and Guidance for Using the ANSI/IES TM-30." Technical Report
RSC Inorganic Chemistry Frontiers (2022). "Efficient violet-light-excitable blue-cyan phosphor for full-spectrum lighting."
The Electrochemical Society (2009). "Phosphors for LED-based Solid-State Lighting." Interface