Disclaimer: I was given the high CRI LED bulb from Prometheus Light free of charge for testing purposes.
Manufacturer website: https://darksucks.com/products/ultra-high-cri-led-lightbulb
The main specs by the manufacturer:
-CRI (Ra) 95, R9 85
–2700K color temperature
–8W power rating
-A19/A60 standard bulb size
-AC input voltage 240V, also available in 120V
–30000 hour lifetime
-Low blue light emission
–3 year warranty
Three bulb samples were tested.
Bulbs came in unmarked cardboard boxes.
Eight filaments in a 2P4S string.
E27 socket without any markings.
Driver visible at the base.
Measurements were made in a 50cm integrating sphere with an x-rite i1pro spectrometer after the bulbs had warmed up for 1 hour. Intensity (lux at 1 meter, candela) was measured outside the sphere at 50cm.
The bulbs were connected to mains power which at the time of testing was at 227-228V.
Output at 1 hour is 511-537 lumens. This fits inside the manufacturer’s spec of 500-600 lumens.
Power consumption was measured at 6.7-6.9 watts. Efficiency is ok for a warm and high CRI light source at 76-79 lumens per watt.
Maximum output is reached immediately. Light output in lumens was plotted over one hour for one bulb sample. The output decreased only 7 percent during the 1 hour warm up period from 571 to 529 lumens.
Some intermittent output change was noted during the first 30 minutes of the runtime test, but visual changes weren’t detected.
CRI data was measured integrated after a 1 hour warm-up in an integrating sphere.
One of the three tested bulbs (#2) was an outlier. Its tint was closer to the black body line and color rendering indices were slightly lower. The CRI R9 (deep red) was ten points lower than on the other two samples.
The actual visual difference is minimal though. CIEDE2000 color difference measurement between bulbs 1 and 2 showed a value of less than 1, which means that the difference should be below the detection threshold of an average person.
Color rendering is very good reaching CRI Ra of 96-97 and R9 of 77-87. TM-30-18 fidelity index Rf of 92-94 and gamut index Rg of 97-99 are also good.
Typical LED phosphor technology is evident from the minimal blue hump at 460nm, but as the color temperature is low the total energy at the blue wavelenghts is very small and shouldn’t interfere with sleeping hormone levels.
Overall the spectrum is very similar to the 3000K Yuji A60 bulb (YJ-BC-RP-10-30) I tested earlier.
Visually the light is very pleasing bringing out especially red and brown shades superbly. As an incandescent replacement it works really well.
Due to the almost vertically oriented LED filaments and the lack of bulb diffuser, the intensity is very low when measured directly below the bulb. Highest intensity was measured at ~90 degrees i.e. to the side of the bulb. Some care needs to be taken when installing the bulbs because of this.
Load IES TM-30-18 Color Rendition Reports by clicking the thumbnails:
CGATS CRI Data files:
Bulb 1: https://pastebin.com/K6PvVA4S
Bulb 2: https://pastebin.com/7j8kiWbe
Bulb 3: https://pastebin.com/mbtetcUs
Installed in a typical lamp fixture (Ikea Tertial) the intensity is higher at 130 cd thanks to the reflector. There are some radial artifacts present so the bulb isn’t necessary suitable for critical work. Good tint was retained with the Ikea fixture at 2743K and duv –0.0010. CRI even improved to Ra 98 and R9 96 while TM-30 stayed the same as integrated at Rf 94 and Rg 99.
Color temperature and tint
Tint is slightly below the black body line on two of the bulbs an right on it on one. In part thanks to the low power consumption the tint and CCT stabilize pretty quickly, in about 10 minutes.
Tint shift is very small at usable irradation angles (>20°).
No visible flicker.
The non-existent modulation depth at 100 Hz and a snob index of 0% guarantees that it’s easy on the eyes. The light is also suitable for video.
AC power draw
There’s power factor correction in the driver circuit, which results in a power factor of over 0.9. Power is drawn gradually as soon as the AC voltage waveform crosses zero.
The current waveform is closer to resembling a sinewave than on most LED bulbs, whis should also mean that dimmer compatibility is better than average.
Cyan line: mains line voltage
Yellow line: current draw of the bulb
Violet line: power draw (voltage * current)
The Prometheus high CRI LED bulb is a direct drop-in replacement for an incandescent. It matches the color temperature while offering good color rendering and tint. The result is visually very pleasing while having zero flicker.
In many ways the Prometheus high CRI bulb is a cheaper but equally capable alternative to the Yuji 3000K BC series A60 bulb I tested earlier. In color rendering and tint they are practically identical, but the Yuji edges ahead in effciency and output. At $12 a piece the Prometheus offers better value than the $20 Yuji.
One bulb out of three showed a slightly different spectrum. The small difference in tint and R9 (deep red) rendering shouldn’t be visible to the average observer.
Some care should be taken when choosing the fixture for the Prometheus bulb, since the radiation pattern is uneven with regard to intensity. Tint however is very consistent at every observation angle. A diffusing light fixture or a matte reflector works best, but some darker areas may be visible on a flat even surface. Due to these reasons the light is ideally suited for general ambiance or mood lighting instead of task lighting where lots of even light is needed over a small area.
Please note that the test was done when the bulb was brand new. I can’t guarantee that they will perform similarly after months or years of use.