One of the special color rendering indices, measuring fidelity for a saturated red test color. White LEDs built from a blue chip and yellow phosphor often score low or even negative R9 because their spectrum is weak in deep red, which makes skin, wood, meat and red fabrics look dull. Specifiers add a minimum R9, often 50, to CRI requirements in retail, healthcare and hospitality.
CRI's 92 but R9 is only 12, so skin tones in the exam rooms are going to look washed out.
Ask for the full R1 to R15 table: a high Ra with a weak R9 is the classic way a cheap LED passes a CRI spec.
Also heard as
- R9 value
- special color rendering index 9
Related terms
CRI
Color Rendering Index: a score up to 100 for how true surface colors look under a source compared with a reference light.
TM-30
A color rendition method that rates fidelity and saturation with 99 color samples, giving Rf, Rg and a color vector graphic.
SPD
Spectral Power Distribution: a graph of how much power a light source emits at each wavelength.
LED
Light-Emitting Diode: a semiconductor light source, made white for lighting by coating a blue chip with phosphor.