CRI (Colour Rendering Index) is used to measure how a given light source will replicate the appearance of particular pastel shades. The ability of being able to calculate this properly means that by process all other colours should also be processed naturally.
R9 values are not usually shown by sellers of LED strips, who may just simply advertise their strip as having a CRI rating of 90+. At Hi-Line, we make sure to include such information in our "photometric measurement" files, which can be downloaded.
An R9 value doesn't necessarily have to be extremely high, as a small amount can be traced in each colour that makes up the CRI chart, although it is important that R9 in any calculation be higher than zero - zero obviously being an absolute minimum; the higher you can achieve, the better. An overall CRI rating would be exemplary at 90 and above, whereas R9 as an individual figure would be ideal at around 50. All of our CRI-rated strips have a high R9 value.
So, why is R9 so important?
Say, you're lighting for restaurants, retail outlets, museums, or hospitals. It stands to reason that you would want to achieve natural-looking reds, whether it be to maximise the efficiency of work being carried out, or to appease a customer's eye. Without an appropriate R9 rating, regardless of whether or not the overall CRI is 80 or above, certain objects/liquids will appear discoloured in some way, which can result in having a negative impact. Of course, in the home, we also want to have appealing, natural colours for all occasions.