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Whenever LED light quality is discussed—especially in terms of color rendering—it’s just a matter of time before the R9 value is mentioned. So what exactly is this point of dissention in LED lighting circles? Is the R9 value really that important?
The R9 value is one of the 14 pigment colors scientists have established to measure color rendition. However, Color Rendition Index (CRI), which is the baseline measurement used to determine how well colors from a light source compare against those from a “natural” light source such as sunlight, does not account for the R9 value. In fact, CRI only measures the light source against the first 8 pigment color samples:
The R9 value produces strong, vibrant reds. Is it really important to include a strong red when measuring color rendering? No, it’s not important. It’s fundamental. Paramount. Vital. Essential. Critical. Take your pick of adjectives.
Why should we care?
People should care because strong reds are prevalent in skin tones and clothes. Food retailers should care because strong reds are prevalent in grocery store produce and meats. Gallery owners and artists should care because strong reds are prevalent in art work. Hospitals should care because strong reds are the most critical color for surgical procedures.
The R9 value is so important, that some utility companies are now offering rebates for positive R9 value lamps.
Can you get a reasonable colour rendering without a good R9? For most applications you can, but where red reproduction is of paramount importance you need to look further. Energy Star defines an acceptable CRI as having a value greater than 80 and an R9 value greater than zero and this produces very good light quality and colour reproduction. However many LED products fail to meet these standards. Further, when it’s really critical to produce good reds of the quality produced by halogen or incandescent lamps (such as the vegetable or meat counter at your local grocery store) you need to look for a lamp with a CRI above 90 and an R9 above 60. It’s worth noting that R9 does track with increasing CRI, but because the measure is in effect an average value, it’s only at very high CRI’s that R9 tracks closely.
Aside from using a different set of standards in which to judge LED light quality (see Attention CRI: You’re no longer relevant), what can you do to ensure the LED lamp you want to buy renders color accurately?
All of Leapfrog’s specialised high CRI products have a CRI of at least 95 and an R9 over 80.