CRI, CCT, and UGR: Specifying Quality of Light

Why quality of light matters

When most people think about lighting quality, they think about brightness — "is there enough light?" But brightness is the most basic quality of light. What really distinguishes good lighting from bad lighting is not how much, but what kind.

Three metrics define the quality of light more than any others: CCT (color temperature), CRI (color rendering), and UGR (glare rating). Together they determine whether a space feels comfortable, attractive, and high-quality — or harsh, cheap, and institutional.

For specification-grade architectural lighting, these three parameters are as important as wattage or lumen output. They are the difference between a space that feels expensive and one that feels cheap — even if the quantity of light is exactly the same.

CCT: Correlated Color Temperature

Color temperature describes the color appearance of white light, measured in Kelvin (K). Lower numbers are warmer (more yellow/amber), higher numbers are cooler (more blue/white).

Choosing the right CCT

Color temperature is not a "better/worse" metric — it is about appropriateness for the application:

• 2200K-2700K — Hospitality, residential, restaurants, lounges. Warm, intimate, cozy. Makes food and people look good. Feels like candlelight or incandescent.
• 3000K-3500K — General commercial, retail, healthcare, education. Warm but functional. The most versatile temperature for mixed-use spaces.
• 4000K-5000K — Offices, laboratories, industrial. Cooler, more alert, more energetic. Associated with daylight and productivity.
• 5700K+ — Industrial, outdoor security, specialized applications. Very cool, stark, and blue-heavy.

Color consistency: MacAdam ellipses

Two fixtures with the same rated CCT can look different in real life. The industry measures color consistency using MacAdam ellipses (or SDCM — Standard Deviation of Color Matching):

• 1-step MacAdam. Color difference is imperceptible to the human eye. For the most demanding applications.
• 3-step MacAdam. Minimal visible difference. Standard for specification-grade projects.
• 5-step MacAdam. Visible difference between fixtures. Acceptable only for non-critical applications.
• 7-step+ MacAdam. Obvious color variation. Not acceptable for architectural lighting.

Always specify 3-step MacAdam or better for projects where multiple fixtures will be seen together. Color inconsistency between adjacent downlights is one of the most obvious signs of low-quality lighting.

CRI: Color Rendering Index

Color Rendering Index measures how accurately a light source reveals the colors of objects compared to a reference source (daylight or incandescent, depending on CCT). The scale is 0-100, with 100 being perfect color rendering.

What CRI actually measures

CRI is calculated from 8 test color samples (R1-R8). The CRI number (Ra) is the average of these eight values. There are also 6 supplementary test colors (R9-R14), including R9 (saturated red), which is particularly important.

This is important because a high Ra number does not guarantee good rendering of all colors — especially reds. A fixture with Ra 90 could have R9 as low as 0, meaning reds look dull and lifeless. That is why good specifications always include an R9 requirement.

CRI levels and applications

• CRI 70-80 (Ra) — Basic commercial, industrial, warehouse. Colors are not vivid but functional.
• CRI 80+ (Ra) — Standard commercial, office, education. Acceptable for most general applications.
• CRI 90+ (Ra) — High-quality architectural, retail, hospitality, residential. Colors are vivid and accurate.
• CRI 95+ (Ra) — Premium applications, art galleries, museums, high-end retail. Near-perfect color rendering.
• CRI 98+ (Ra) — Museum and gallery grade. The highest commercially available.

Beyond CRI: TM-30

CRI was developed in the 1960s and 70s and has well-known limitations. TM-30-15 is a newer, more comprehensive metric developed by the IES that uses 99 color samples instead of 8, and reports both fidelity (Rf) and gamut (Rg).

TM-30 provides a more complete picture of color rendering quality, but CRI is still the standard that most specifiers use and most products specify. For critical applications, consider specifying both Ra and TM-30 Rf.

UGR: Unified Glare Rating

Glare is the most underrated quality-of-light issue. A space with adequate light levels but high glare will feel uncomfortable, cause eye strain, and look cheap. Yet glare is rarely specified — most projects only look at average lux levels.

UGR (Unified Glare Rating) is the standard metric for discomfort glare in interior spaces. It is calculated based on the luminance of light sources, the background luminance, the size of the sources, and their position relative to the viewer's line of sight.

UGR values and applications

• UGR 16 — Very low glare. For demanding visual tasks — drawing offices, design studios, laboratories.
• UGR 19 — Low glare. Standard for offices, classrooms, and general work spaces.
• UGR 22 — Moderate glare. Acceptable for corridors, storage, and non-task areas.
• UGR 25 — High glare. Generally unacceptable for spaces where people spend extended time.
• UGR 28+ — Very high glare. Severely uncomfortable.

UGR depends not just on the fixture but on the room — its size, reflectance of surfaces, and fixture layout. A fixture with good glare control in one room might have poor UGR in another. Always calculate UGR for the actual room conditions using DIALux or similar software.

How the three metrics interact

CCT, CRI, and UGR do not exist in isolation. They interact in important ways:

• CCT and CRI. CRI is measured relative to a reference source of the same color temperature. You cannot directly compare CRI values across different CCTs. Also, warmer light generally has better perceived color quality even at the same CRI.
• CCT and glare. Higher CCT (cooler) light appears brighter and more glaring than the same physical intensity at lower CCT. A 4000K fixture at the same luminance as a 2700K fixture will feel brighter and more glaring.
• CRI and perception of brightness. Higher CRI light can make a space feel brighter than lower CRI light at the same illuminance level, because objects are more visible and the scene has more contrast.
• All three together define quality. A space with correct CCT, good CRI, and low glare will feel high-quality and comfortable — even at relatively low light levels. A space with wrong CCT, poor CRI, and high glare will feel cost-effective and uncomfortable — even if the light levels are high.

Specification guidelines by application

These are starting points, not hard rules. The right specification for any project depends on the design intent, the user group, and the architectural context. But these three metrics — CCT, CRI, and UGR — are the foundation of any quality lighting specification.

At Yakeen, all our standard products offer 3-step MacAdam color consistency and CRI 90+ with R9 > 50. We also offer higher CRI options (95+) for the most demanding applications. And we provide full UGR data and DIALux calculation support so you can verify glare performance in your specific project.