In short
- Ra averages eight pastel colours. The materials that define Indian interiors, such as teak, rosewood, laterite, terracotta, brass and skin, depend on saturated reds and warm hues that Ra does not test.
- R9 is the quickest check for red. TM-30 is the fuller picture: Rf for accuracy, Rg for saturation, and a colour vector graphic showing which hues shift.
- Set rendering by the most demanding surface in a space, and judge it on the real material at mock-up.
Why Ra 90 can still look wrong
Ra (the general colour rendering index) is the average of eight test colours, R1 to R8. They are all moderately saturated pastels. A light can score well on them and still render strong reds poorly.
- R9 (saturated red) is excluded from Ra. Many LEDs with Ra 80–90 have low R9.
- Averages hide failures. A high Ra can sit alongside one weak hue that matters to your finish.
- Ra says nothing about saturation. Two lights with the same Ra can make the same fabric look duller or richer.
The framework for colour temperature, rendering and consistency is in The Colour of Light.
TM-30 in practice
IES TM-30 evaluates 99 colour samples drawn from real objects and reports:
- Rf (fidelity, 0–100): overall accuracy compared with a reference source. Think of it as a more robust Ra.
- Rg (gamut, around 100): average saturation. Above 100, colours look richer; below 100, duller.
- Colour vector graphic: a circle showing how each hue shifts in saturation and direction. This is the most useful part for designers.
- Local values (Rcs, hj): saturation change for each of 16 hue bins, including reds.
A source with Rf 92 and Rg 102, with a slight red boost, usually flatters skin, timber and food. A source with Rg 110 and strong red push looks theatrical and can make complexions look flushed.
Material by material
Skin
- Faces depend on red and orange. Low R9 makes skin look grey, waxy or tired.
- Dining tables, dressing areas, bathrooms, boardrooms and video-call spaces deserve the highest rendering in a project.
- Target: Ra ≥ 90, R9 ≥ 50; Rf ≥ 90 with Rg 100–105 where faces are the focus (convention).
Teak, sheesham and rosewood
- Warm timbers need warm CCT and good red rendering together. Either alone is not enough.
- Under weak red rendering, teak reads brown-grey and veneers lose depth.
- Test samples on the actual veneer with its finish; lacquer and oil change the result.
Laterite, terracotta and sandstone
- Odisha’s laterite and terracotta are red-orange materials. They dull badly under low-R9 sources.
- On facades, the effect is magnified because grazing exaggerates texture and colour together. See Facade Grazing on Stone and Laterite.
Marble and white stone
- White marble shows tint more than poor rendering. Duv and colour consistency matter more than R9 here.
- Veined and coloured marbles benefit from good fidelity; a cool, low-fidelity source flattens veining into grey.
Food
- Restaurants and dining rooms are judged on food. Reds (tomato, meat, chilli), oranges and greens all need fidelity.
- A slight increase in red saturation is common in hospitality; too much looks artificial.
Textiles and art
- Silk, saris and art have saturated colours across the spectrum.
- Look at the full TM-30 vector graphic, not just averages, and keep UV and heat away from sensitive pieces.
A specification by surface
| Surface or space | Minimum (convention) | Better for critical work |
|---|---|---|
| Faces: dining, dressing, boardroom | Ra ≥ 90, R9 ≥ 50 | Rf ≥ 90, Rg 100–105 |
| Warm timber and stone | Ra ≥ 90, R9 ≥ 50 | Rf ≥ 90 |
| White marble and plaster | Ra ≥ 90 | Tight Duv and SDCM |
| Restaurants and retail food | Ra ≥ 90, R9 ≥ 50 | Rf ≥ 90, Rg 100–105 |
| Art and textiles | Rf ≥ 90 | Review vector graphic |
| Circulation and back-of-house | Ra ≥ 80 | — |
These are working conventions for premium projects, not code requirements.
At mock-up
- Compare two or three candidate fittings side by side on the actual finish, at the intended CCT and dimming level.
- Include a face. A person standing in the light reveals rendering problems faster than any sample board.
- Ask for TM-30 reports measured on the complete fitting, not just the LED.
- Check at low dimming levels too; some sources shift as they dim.
Specification notes
- Specify Ra and R9 on every fitting; add TM-30 Rf and Rg for critical spaces.
- Set the minimum by the most demanding surface in each zone.
- Ask for TM-30 data on the complete luminaire.
- Mock up on real finishes with a person in the light before approval.
- Avoid strongly oversaturated sources (Rg well above 105) except for deliberate effect.
Frequently asked questions
What is a good R9 value?
For residences and hospitality, R9 of 50 or more is a practical minimum. For dining, dressing and art, higher values are better. Many standard LEDs report R9 below 20.
Is TM-30 better than CRI?
TM-30 tests 99 real-object colours and reports both accuracy and saturation, so it describes more than Ra. For routine areas Ra and R9 are adequate; for critical spaces TM-30 is more informative.
Why does wood look grey under some LED lights?
Usually because of weak red rendering (low R9) or too cool a colour temperature. Warm timbers need both warm light and good red content.
Continue the series
- The Colour of Light: CCT, CRI and TM-30 for Architects
- 2700 K vs 6500 K in Indian Homes
- One Wall, Two Whites: Colour Consistency
- The Kitchen and the Dining Table
About the author
Prem Rout, Founder of JMAP Solutions, set up in 2022 to deliver lighting, automation and building management solutions from Bhubaneswar. Over 15 years of experience in building products, construction and project business development across Mumbai and Odisha, working where design intent meets specification and site delivery. Connect on LinkedIn.
