Color Rendering Index (RA) and Color Temperature. The influence of LED color rendering index on color perception

In this quick review, I tested 10 different LED light bulbs using a spectrophotometer. Impressions and detailed information are under the cut.

As a testing tool I used a USB-650 Red Tide spectrophotometer: ($1840 + shipping).
There will be a minimum of photos, mostly graphics, and features.
We will look at two main parameters (I will give a very simplified, “kitchen” description):
Correlated Color Temperature (CCT). Roughly speaking, the higher this value, the more bluish the color; the lower, the more it leans toward orange. The optimal value is considered to be from 4500K to 6500K. The specific meaning is a subject of debate and discussion; science has not yet come to a concrete solution.
Color rendering index, color rendering index (CRI or Ra) is a parameter characterizing the level of correspondence of the natural color of a body to the visible (apparent) color of this body when illuminated by a given light source. The higher the better, but visual visibility also decreases. Let's say the difference between 60 and 70 is much more noticeable than between 70 and 80.
If you are interested in a more detailed description of these parameters, then the wiki has articles on the topic:

And I'll move on to the review.
I'll start with the light bulb, which is in the title. There are many options there. I took the non-dimmable 85-265V, 8W model. I took this model because I wanted it with a normal driver so that it wouldn’t flicker. Unfortunately, it flickers and is quite noticeable.

The color rendering index is -86, which is very, very good, but the color temperature of 2577K is approximately the same as a 220-volt incandescent light bulb, if turned on at about 160 volts. Visually, it is more like sodium lamps for outdoor lighting. Apparently, it flickers noticeably at twice the network frequency, so I won’t recommend it.
No. 2 - Corn for 263 pieces of 5mm diodes with DD4:
(The link is dead, don’t go in vain)

What can I say? - p-t-t, not a light bulb. It blues terribly, as can be seen from the color temperature - as much as 22663K, and the color rendering index is 71.7, which is also not a fountain. You probably don’t need to write about the fact that it flickers like hell, and it’s clear that the light bulb is trash.
No. 3 - Little corn from Gearbest:

Also bluish - 8209K, and the color rendering index is also not so hot - 70.4. Among the advantages, I note the presence of a normal driver and the absence of flicker, so it’s quite possible to go into the hallway, onto the landing, and so on.
No. 4 - Small light bulb with DD4:

It is also a little blue, but quite tolerable. There is noticeable flickering due to the capacitor ballast used. For non-residential premises - it is quite possible. CRI=68.4, CCT=7648K
No. 5 - Magic Blue light bulb from Gearbest:

The color temperature here is 3207K, the color rendering index is quite high - 82.7, and there is no flicker at the mains frequency, or twice the mains frequency, either, but there are two noticeable drawbacks: 1 - Low power, approximately equivalent to a 25W incandescent lamp, and the brightness is controlled by PWM, so At low brightness the flickering will be noticeable.
No. 6 - Mini corn with Cndirect:
(The site is terribly glitchy)

The color temperature is 3163K (tolerable), but the color rendering index is 59.2, so the color is more like car fog lights than an incandescent lamp. In addition, the circuit has a ballast capacitor, but the filter was not installed at all, so it flickers terribly. I don't recommend buying it at all.
No. 7 - Light bulb with imitation filaments from Buyincoins:

In terms of the quality of the measured parameters - Color rendering index - 85.8, color temperature - 6575K, this is the light bulb that is the champion of this review, and its light is very pleasant, but as always, they spared the capacitor in the filter, so we have a terrible flicker with double the mains frequency. So you can only recommend it if you improve your nutrition.
No. 8 - A 5W ice light bulb purchased offline for $3, cool white:

CRI=75, CCT=8630K, which in human language means a slightly noticeable blue tint, and so-so color reproduction. One of the advantages is the absence of flicker, because there is a pulse driver.
The next two positions are light bulbs of a different operating principle, I provided the results for comparison.
No. 9: General Electric Energy Saving 6500K:

There is a very interesting spectrum, which is fundamentally different from the spectrum of LEDs - we have several pronounced peaks. In total, 8234K and 76.2 are indicators at the level of an average ice light bulb, nothing special. I especially didn’t like the peak at 365 nm - this is already ultraviolet, very undesirable for the eyes, and its intensity is high. The pluses are the absence of flicker and normal workmanship.
No. 10 - 77W halogen lamp OSRAM:

A monotonous, beautiful line, monotonously growing towards IR. CCT=2809K, CRI=97.7 Flicker is not noticeable. In general, great, if not for the terrible heating.
Total. In this review, I looked at 8 LED light bulbs purchased from popular online stores. As you can understand from the text and graphs, it won’t work just like that and replacing a regular incandescent lamp with them - either the flickering is strong, or the color temperature is low, or the color reproduction is poor. You might get the impression that LEDs are bad. No matter how it is, I would say differently - Inexpensive LED light bulbs are bad. And for comparison, I’ll give you the spectrum of an expensive LED light bulb, which costs not $2-5, but $30:

+ You need a native driver (Chinese ones are not suitable), which costs about $20, and a radiator (let’s say $10). So what do we get by spending “only” $60 on one light bulb?

3517K and CRI=89.5 - Very, very decent. Naturally, there is no flicker. Visually, the light is like a good, sunny day, at 3-4 o’clock in the afternoon, in the middle zone. Expensive, would you say? I agree, it’s expensive, but for me personally, my health and the health of my children are more important.

I'm planning to buy +10 Add to favorites I liked the review +43 +66

Color rendering index(color rendering coefficient, CRI) - a parameter characterizing the level of correspondence of the natural color of a body to the visible (apparent) color of this body when illuminated by a given light source. It is currently the only internationally recognized color rendering rating system that provides some guidance to consumers.

The thing is that when lighting objects with different types of lamps, we see that the result may differ. We are talking about color rendering, how an object will look in the light of a particular lamp. In some cases, the colors will look more accurate and natural, while in other cases they will look completely different from sunlight. It turns out that two different types of lamps can have the same color temperature, but transmit colors differently. The emission spectrum of lamps is uneven and their color rendition depends on the energy of the lamps in one or another part of the spectrum. For example, General Electric SP and SPX fluorescent lamps have approximately the same color temperature as incandescent lamps, but the former have much less energy in the red region of the spectrum. This makes red colors appear brighter under incandescent lighting than under fluorescent light sources.

The color rendering characteristics of a lamp describe how natural the objects around us look in the light of this lamp. And for a quantitative measure, the color rendering index is used. This is a relative value from 0 to 100, which characterizes the level of correspondence of the color obtained when illuminated by the tested lamp to the natural color of the body. 100 corresponds to a complete match as in sunlight, i.e. colors from such a light source are transmitted as accurately as possible. Incandescent lamps are close to this. Color rendering index has the designation R a, also known as CRI - color rendering index.

The term appeared around the 1960s and 1970s. CRI was originally developed to compare continuous spectrum light sources that had a color rendering index above 90, since below 90 it is possible to have two light sources with the same color rendering index but with very different color rendering.

How color rendering coefficient is measured:

To determine it, 8 or 14 test colors specified in DIN 6169 are used (six additional colors are sometimes used for special needs, but they are not used to calculate the color rendering index), which are illuminated by the test lamp and then by a reference lamp having the same color temperature. The smaller the differences in color rendering between the test colors, the better the color rendering of the lamp under test. Which, depending on the index value, characterizes the lamp as having low, sufficient, good or very good color rendering.

The smaller the deviation of visible color from natural color (the higher the color rendering index), the better the color rendering characteristics of this light source.

A light source with a color rendering index of R a = 100 emits light that optimally displays all colors. The lower the R a values, the worse the colors of the illuminated object are reproduced:

There is a system that mathematically compares the change in location on the spectral scale of colors compared to the same colors illuminated by a reference light source. The average differences are then subtracted from one hundred to produce the color rendering index.

Tested colors (primary):

Comfortable for the human eye CRI value from 80-100 R a . LED lamps are good in this regard.

By definition, if there is no difference in how the colors of objects appear, the light source is assigned a CRI of 100. Thus, small differences will result in a CRI closer to 100, while larger differences will result in a lower CRI value. When comparing color temperatures in the range from 2000 K to 5000 K, the reference light source is the blackbody emitter, and with color temperatures above this range, daylight.

It is noteworthy that the color rendering index of both incandescent lamps and the northern hemisphere sky is considered equal to 100, despite the fact that neither of them is truly flawless (incandescent lamps are very weak in illuminating blue tones, and the northern sky at 7500 K, in turn , weak in red tones).

Sunlight: R a 100
Fluorescent lamps with 5-band phosphor: R a 90
Metal halide lamps: R a 70 - 90
Standard fluorescent lamps: R a< 75
Sodium discharge lamps: R a 22

Differences in CRI values less than five units are insignificant. This means that light sources with color rendering indices of, say, 80 and 84 are essentially the same.

Technically, color rendering index can only be compared between light sources that have the same color temperature. However, as a general rule, light sources with high color rendering indices (80-100) tend to make people and things look better than light sources with lower CRIs.

Practical tips:

In furniture showrooms, it is best to use warm light. To maintain a calm and pleasant atmosphere, lamps with a color temperature of 2500 - 3500 K and a color rendering index R a of 85 are ideal.

Paints, curtains, fabrics and wallpaper require clear visibility. Here you should choose a light source with a color rendering index R a 90-100 and a color temperature of 5000 K and above.

Wooden furniture + warm light = great combination. The best choice of light source: color rendering index is R a 80-85, color temperature is 2500-3500 K.

For lighting leather products (chairs, chairs, shoes, etc.), warm light with good color rendering (R a 80-90 and 2500-3500 K) is better suited.

According to the applicability of light sources:

The color rendering index is also required to classify light sources, so that later you can understand which lamps are suitable for a particular use.

Theoretically, the maximum value of this indicator is 100. The lower the color rendering index of a particular lamp, the worse it conveys color shades.

In practice, color rendering indices are divided into several levels. DIN 5035 distinguishes six levels.

Level lamps A1 used in lighting systems where color accuracy is one of the most important requirements - in printing, museums, clothing stores.

To lamps with color rendering level 1B include 3-component fluorescent lamps, which are installed mainly in administrative buildings, schools, sports and industrial facilities.

Level lamps 2A have fairly good color rendering characteristics.

Level lamps 3 apply in heavy industry where color accuracy is not important.

Lamps with color rendering level 4 , with the exception of in special cases of high pressure sodium lamps(Ra=20), should not be used indoors. Such requirements for the characteristics and color rendering levels of lamps for rooms of various types and purposes are provided for by the DIN EN 12464-1 standard.

Everyone who understands the light quality of LED lamps and everyone who has read my articles about LED lamps knows about such a parameter as the color rendering index (CRI, also known as Ra). It is believed that high-quality light for residential premises should have a CRI of at least 80.

I recently came across a lamp whose CRI was quite decent - 83.4, but it gave off a very unpleasant greenish light.

I tried to figure out what was wrong with her.

Color rendering index or color rendering index - CRI (ru.wikipedia.org/wiki/Color Rendering Index) - a parameter characterizing the level of correspondence of the natural color of a body to the visible (apparent) color of this body when illuminated by a given light source was proposed in 1965.

CRI is the average level of transmission of eight colors R1-R8.

Sometimes, in addition to CRI, the red color transmission index R9 is indicated and measured. This index affects the quality of human skin tone. On lamptest.ru the measured R9 index is indicated on the card of each lamp.
Back in 2007, the International Commission on Illumination noted that “...the color rendering index is generally not applicable to predicting the color rendering parameters of a set of light sources if this set includes white LEDs,” but it so happens that all LED lamp manufacturers use CRI.

In 2010, to more accurately assess the quality of color reproduction, the Color Quality Scale (CQS) technique was developed, which evaluates the quality of light using fifteen colors.

In 2015, the TM-30-15 standard was developed, which evaluates the quality of light in 99 colors.

For good lamps, the values of all three indices are approximately equal.

Now let's return to the Gauss 207707102 190Lm 2W 2700K G4 12V lamp, which is why I started this whole study. Her color indexes look amazing.

The CRI value is quite high - 83.4, TM30 Rf - 84.3, but the CQS is very low - 35.8. It seems that the cunning Chinese mixed the phosphor so that exactly those 8 colors that are taken into account when measuring CRI are well reproduced. Surprisingly, the result of what seems to be the most advanced index, TM30, also turned out to be high.

I note that out of all 1244 lamps whose parameters I measured, only one had such a low level of the CQS index. Even the worst unnamed Chinese light bulbs with a CRI of 60 have a CQS of at least 50.

I started studying the CQS values of lamps and found out that there are quite a lot of lamps with a CRI greater than 80, and a CQS value slightly above 70, but the light from such lamps is visually quite comfortable. But for some lamps with a CRI of more than 80, the CQS turned out to be about 60 and the light of such lamps is visually greenish or yellowish.

The question arises, what to do with all this. You will probably have to add the CQS value to lamptest and take it into account when calculating the final rating of the lamps, so that it cannot turn out that a lamp with a high CRI, but an uncomfortable light, received a high rating.

P.S: For the development of the lamptest.ru project I am looking for

1. PHP programmer ready to help with website development.

2. Assistants ready to deal with the purchase and return of lamps in stores.

3. Laboratories with a photometric ball, ready to measure the luminous flux of a dozen of my samples for free (to confirm the accuracy of my measurements).

4. The person who made the formula for calculating the quality assessment of lamps in Excel (I went through everything, I can’t find the contacts).

2017, Alexey Nadezhin

The color rendering index (or coefficient) (symbol: CRI - color rendering index; R a) shows how accurately or reliably the light source conveys the colors of the illuminated objects compared to sunlight or. The higher this indicator, the more natural or natural the colors of the objects around us look. Of course, this is only true for people without serious visual defects and color perception disorders. They don't have to read this article.

Determination of color rendering index

The color rendering index is a relative value that can take values from 0 to 100 and characterizes the degree to which the color of a body matches its natural color when illuminated by a certain light source. According to the CIE (1995) methodology developed by the International Commission on Illumination, CRI is calculated from the difference in chromaticity resulting from the comparative illumination of eight standard colors between the test sample and a reference illuminant having the same . The smaller the average difference, the higher the CRI value.

Color rendering index value

A comfortable CRI value for a person (and his eyes) ranges from 80 to 100. Lower values indicate that some colors may not look very natural. Thus, the main natural light source for all earthlings and Martians - the Sun - has the best color rendering with R a = 100.

Color rendering index can be so different!

Color rendering index of incandescent lamps

The light of incandescent lamps is not far from the sun. Their color rendering index is the highest among all artificial light sources and is close to 100, which allows for ideal color reproduction. IKEA candles and a burning mattress can help you achieve equally impressive results, but we don't recommend doing this at home. Unless you're visiting.

Color rendering index of halogen lamps

They are no worse than ordinary incandescent lamps in terms of color rendering, so you can safely use them, if, of course, you manage to connect them correctly.

Color rendering index of fluorescent lamps

Most modern fluorescent lamps from well-known manufacturers have fairly high CRI values: from 80 to 90. But in any case, you should pay attention to the characteristics on the packaging - unpleasant surprises may await you (R a< 75) от очень уж бюджетных моделей.

Color rendering index of LED lamps

Although the color rendering index of the best LED lamps can reach values of 80 or higher, just like good fluorescent lamps, it must be taken into account that there are still quite a lot of lamps on the market with poor color rendering, not counting other disadvantages associated with the peculiarities of using LEDs.

Color rendering index of high pressure discharge lamps

Everything is very bad. Mercury and sodium lamps have the lowest CRI, not reaching 40. However, it is worth highlighting metal halide lamps, which also belong to high-pressure gas-discharge lamps, but the technologies used in them made it possible to achieve a color rendering index of 90 and higher.

With all the variety of modern light sources in everyday life and indoor lighting, the leading ones are LEDs and fluorescent lamps; their main problem and topic for discussion is not energy saving, but the color rendering index and light quality. This is a parameter that largely determines comfort when working under artificial light. In this article we will talk about what color rendering index is, what it should be and how it is measured.

Definition and historical background

The color rendering index is a value obtained from the ratio of the real color to the visible or apparent color of objects. In other words, it shows how true the colors of objects illuminated by an artificial light source are. It is designated as Ra or CRI, short for English. Color Rendering Index, which literally translates to “Color Display Index”.

CRI is just one method for determining color rendering. It is mandatory for testing light sources by all manufacturers. This definition appeared around 1960–1970. Until 1974, color rendition was checked by comparing a set of 8 colors, after which 6 additional colors were added. As a result, when measuring the color rendering index (coefficient), 8 or 14 colors are used; they are specified in DIN 6169.

In this case, the mandatory check consists of comparing the first 8 colors of the spectrum; comparison of 14 colors is carried out if necessary or for special purposes, but they are not taken into account when calculating the index.

Color Rendering Index Measurement

Color rendering index is measured when developing light sources. To do this, the light source under study is illuminated onto a template or calibration table on which standardized colors R1–R8 are applied.

The next stage is illumination of the verification template with a reference light source and taking readings from instruments to determine colors.

Afterwards, the received data is processed using the CIE method and the deviation of the resulting colors from the reference ones is obtained.

Colors are designated as Ri, where i is the color number. Their names:

R1 – withered rose.
R2 – mustard.
R3 – light green.
R4 – light green.
R5 – turquoise.
R6 – sky blue.
R7 – purple aster.
R8 – lilac.

The result is a number from 0 to 100. A color rendering index of 100 has sunlight. The lower the value obtained, the worse the colors are reproduced. The resulting values can be divided into powers shown in the table below.

I also sometimes add color 9 to the rating - rich red.

DIN 5035 describes where lamps with a certain color rendering level can be used:

DIN EN 12464-1 defines the types of rooms and the required color rendering indices, as well as SNiP 23-05-95 in the appendices as recommendations.

Problems of CRI and its analogues

CRI does not always give accurate readings; the fact is that it was originally developed for light sources with a continuous spectrum. We are talking about the spectral composition of white light; it contains a certain set of colors, which result in a white glow with a certain shade (color temperature).

The spectral composition of light is a set of radiation of different wavelengths (colors) in. The spectral composition can be used to determine the degree of emission of a particular color.

When a light source contains all visible wavelengths in its spectral composition, then such a spectrum is called continuous. Example:

sunlight;
incandescent lamps;
halogen lamps.

The correspondence between visible colors and real ones depends on the completeness of the spectral composition. But not all lamps emit the full spectrum.

Fluorescent lamps have a so-called ragged spectrum. It consists of individual peaks at different wavelengths. If we remember what we said above, CRI does not quite correctly reflect the color rendering index of such lamps.

Reference: In 2007, the International Commission on Illumination noted that "...the commission's color rendering index is generally not applicable to predicting the color rendering properties of a set of light sources if that set includes white LEDs."

Therefore, to improve the accuracy of light flux measurements, in 2010 they developed the CQS method, which stands for Color Quality Scale, or Russian. Color quality scale. But this did not provide a full assessment of the quality of light sources, because it did not take into account the saturation and tone of the illuminated objects.

And in 2015, TM-30-15 appeared - this is a standard that takes into account more parameters, namely, in addition to templates, tone, saturation and objects found in everyday life take part in the assessment.

However, in no country, at the time of writing, TM-30-15 is mandatory, but this does not prevent self-respecting manufacturers from testing products in this way.

Often, when checking the values on the CQS and CRI scales, they give approximately the same results, however, it also happens that the results on TM-30-15 are below normal. An example of measuring poor color rendering of an LED lamp is described in an article from independent experts: https://geektimes.com/company/lamptest/blog/285034/

Most likely, the reason for this result was the phosphor, which was specially selected to pass the mandatory tests, but still does not provide normal color rendition.

Color rendering index of different types of lamps

Next, we will look at typical color rendering indices of different lamps. The index depends on the operating principle and design, as well as the luminaire components used. As already mentioned, sunlight is taken as the standard.

Incandescent lamps

Classic incandescent lamps, although prohibited for use in most countries due to their low efficiency, have a color rendering close to sunlight, close to 100. They have a pronounced shift towards warm colors and the infrared range.

Halogen lamps

Halogen lamps provide greater luminous flux with the same power consumption as incandescent lamps. At the same time, their color rendition is approximately at the same level.

Sodium lamps

Sodium light bulbs are rarely used to illuminate rooms where people work. This is explained both by technical issues, for example, a buzzing throttle, long ignition, and by a low color rendering index - 40 Ra. High pressure sodium lamps, or HPS, are used to illuminate large areas. For example, in street lighting, on lamp posts and floodlights. This application is due to the high luminous flux (150 Lm/W) and long service life, more than 25,000 hours. They belong to gas-discharge light sources. They have a torn spectrum, with a predominance of red-orange tones.

However, they are also used for growing plants in greenhouses and hydroponic systems due to their spectrum. The industry produces special sodium lamps for plants; they express the peaks in the light spectrum necessary for their growth.

DRL

Mercury arc lamps or HRLs are similar in scope to DNAT, with the exception of plant lighting. They have a service life of about 10,000 hours and a high luminous flux of 70–95 Lm/W, and their color rendering index is up to 40 Ra. They also have a ragged spectral composition with a shift towards blue and ultraviolet.

Fluorescent lamps

Tube-type fluorescent lamps and compact fluorescent lamps were especially popular before low-cost LED products entered the market. The main disadvantage is the need to use ballasts, as well as the ragged spectral composition of the light, usually shifted to the region of cold colors, but depending on the phosphor, they can also emit neutral and warm light.

The color rendering index of fluorescent lamps strongly depends on the composition of the phosphor, varying from 60 to 90 or more Ra.

Typical values:

for a three-component phosphor – 80Ra or more;

for a five-component phosphor – 90Ra.

LED bulbs

As already mentioned, the color rendering index of LED lamps depends on the composition of the phosphor with which the LED crystals are coated. The index ranges from 80 Ra, a good result is 90 Ra. They are used in premises of any type, as far as design features allow.

Conclusion

When choosing a light source, you need to pay special attention to the color rendering index, since the accuracy of color perception depends on it. This is especially important if you work with flowers, for example, paint, or choose lighting for a photo studio. In any case, you cannot skimp on lighting, since the health of your eyes depends on it.