High CRI LED vs high CRI OLED, which do you choose?

OLED (Organic Light-Emitting Diode) is no longer a novelty, it is already widely known since display screens of television, mobile phone started with it earlier, now the general lighting industry comes up with this new technology as well. Comparing to LED, some advantages are mentioned frequently as:

  • Self-luminous, super flexible with uniform light distribution (Figure 1 shows the OLED structure), a true “area source” instead of “point source”.
  • No need of crystalline substrate and diffuser.
  • Broad spectrum, close to the natural light.

 

Figure 1. OLED structure (Picture from Arrant-Light Blog).

With the OLED sample we get, which is a high CRI version, nominal parameters are:

  • 105mm*55mm size;
  • Typical 8.5V DC, 80mA;
  • CCT 3000K;
  • CRI Ra>90;
  • Typical luminous efficiency 50lm/W.

 

Testing the items as below:

  • Luminous flux, luminous efficiency;
  • CRI Ra, R1-R15, TM-30-18 Rf, Rg;
  • Chromaticity coordinate, CCT, DUV;
  • Spectrum comparison;
  • Working temperature.

Most of the tests could be processed directly in the integrating sphere, let’s check out with the result (Figure 2).

Figure 2. Color rendition test on high CRI OLED sample.

Not bad, right?
Visual effect quite promising, but we can still sense some problems, as the concluded opinions from us:

Uniformity

This impresses us most, to make a direct comparison, we find an LED panel with similar size (Figure 3) and drive at low current, no diffuser. Imagine how much the lighting designers would love OLED!

Figure 3. Left-LED panel, right-OLED panel.

Spectrum

Although the general color rendering is good, when we compare the spectrum with Yujileds BC series 3000K high CRI LED, the difference is still obvious (Figure 4). The long wave band – which represents the color rendition of red, is narrower and shorter than the current LED phosphor solution we are using, this results in the relatively lower R9 (59), by contrast, currently we already can achieve as high and stable R9 as up to 98. However, R9 is considered as a very important, probably the most important parameter to render skin tone and saturated red.

Figure 4. Spectrum comparison.

Luminous efficiency & cost performance

So far as we know, OLED is not that competitive comparing to LED, especially when we evaluate it based on high CRI feature, while with different technical solutions and by different product modalities, we can control the high CRI (Ra > 95) LED from 40lm/W to 160lm/W, regarding to cost performance, we spend $100 to get this 37lm OLED panel, calculating to lm/$ we feel it is still a kind of luxury product for general lighting applications, at this stage at least.

Working temperature & lifespan

Testing the central temperature after driving the OLED panel of 10 minutes, we see the thermal dissipation is excellent (Figure 5), but considering the total input power is only ~0.07W in the size of 105mm*55mm, with this power density probably the temperature is not that referential.

Unfortunately we do not have suitable equipment for evaluating the stability and lifespan, the vendor provides a proposal on >10000 hours, but we are not sure if it calculated as L70.

Figure 5. Temperature test after 10 minutes.

After the full test, high CRI OLED interests and impresses us, the overall color rendition and light uniformity are beyond our estimation, while the efficiency and cost are not promising, we expect to see the improvements in the future, at this moment we have questions:

  1. The feasibility to adjust the peak wavelength and FWHM of the spectrum.
  2. The flexibility to make different correlated color temperatures.
  3. The capability to control the SDCM.

 

So, what do you think of high CRI OLED?