Received my M21E and M21F with the GTFC 1900k. Here are the measurements for one of them (both are similar):
Stock:
CCT 1946K
DUV 0.0041
CRI 94.9
R9 73.2
RG 85
W/ Quarter Minus Green Lee Filter
CCT 1816K
DUV 0.0020
CRI 95.4
R9 72.1
RG 88
W/ Half Minus Green Lee Filter
CCT 1683K
DUV 0.0003
CRI 92.6
R9 67.1
RG 92
First of all, the quality of the flashlights is great and its nice that for the price, they come with boost drivers and are USB-C rechargeable. However, the GTFC 1900k is not what I expected. First of all, the DUV is very high (above the BBL or yellowish) and it requires a Half Minus Green Lee Filter to bring it down to neutral. Without the minus green filter, it looks pretty bad even to me and and I’m a huge fan of ultra warm lights like the E21A 2000k. Even with the half minus green, it is too warm even for me and the color rendering cannot compare with the E21A. I think the optimal ultra warm temp is 1800k-1900k (candle flame) with neutral or slightly negative DUV. In the future, I hope Simon can request a 9080 version that does not require half minus green LEE filters to bring it down to neutral. The half minus green filter surprisingly lowers CRI and R9.
R9 is only 73.2 which is about the same as CREE and Samsung 90CRI lights. However Nichia offers some high end 9080 that have R9 above 80 or sometimes even close to 100. RGWN that used to sell the GT-FC said he specifically requested the 9080 from Getian because if you don’t ask for it they will just give you 9050, which is likely what Simon and Hank got. IIRC RGWN’s GT-FC tested more like 9595.
RG is the worst I’ve ever seen for a HiCRI emitter at only 85. This means colors are not saturated. The E21A 2000K has a R9 of 100. I’ve tested some mixed tint E21A that reach RG of 107 and colors really pop and look almost cartoonish.
This surely won’t be a replacement for my NOV-MU with 21xE21A 2000k, which is probably as close to perfect candle light as we will ever see in a flashlight. Also the NOV-MU can sustain maybe 3x as much lumens as the M21E or M21F based on my observation. However, the NOV-MU also cost over 3x more and have not been available for purchase for almost 2 years.
The biggest pro for this GT-FC 1900k is that it emits even less blue wavelength than incandescent bulbs and less than the E21A 2000K, which means practically no blue light. Yet it still looks much better than all those yucky yellow light bulbs advertised to help you sleep that Ive tested. This makes for an excellent light for those who like to sleep with lights on as less blue wavelength means less negative health impact. It also makes for a great light that don’t attract insects. With the half minus green filter on, it is 1683K or basically an amber emitter but can sill render colors so it can be treated as a replacement for amber leds.
I do not regret buying these flashlights and I definitely will have use for them such as navigating the house at night without waking up others or leaving them plugged in as night lights.