There are not many Red, Green, Blue, White (RGBW) flashlight/torches around, and thus the Wurkkos WK40 is an interesting flashlight to review. This review is of a prototype/pre-production version, and the final version may be different after feedback from multiple testers.
Disclaimer
The Wurkkos WK40 was sent to me for an impartial review. All links are non-affiliate - I do not make any income from links or sales from this review. This review is written from the perspective of a light painting / night photographer, and flashlight enthusiast.
Construction
The Wurkkos WK40 is a 21700 battery format light, with 33mm head diameter, and length of 123.3mm. The light has red, green, blue, and white LEDs in a quad TIR optic. It has a tail switch for changing modes, and rotary head ring for changing brightness. The light has internal USB-A to USB-C charging. The LED driver is a buck constant current driver. With an IP68 rating, it should handle light rain and a quick dunking in water.
The light arrived in a branded box, with many accessories. A shorter 20350 battery tube was also included, though I'm not sure where to find 20350 batteries in Australia? The package included a 5000mAh 21700 Li-ion battery (unknown OEM), spare O-rings, silicone diffuser, and USB-A to USB-C charging cable. 2 pages of A4 manual were also included. There is no side clip or lanyard included, which I would prefer instead of a rather pointless 20350 tube.
The charging worked with a USB-A to USB-C cable, and USB-C to USB-C cable. An indicator light next to the port flashes red when charging, and green when charged. The charging terminated a bit too early at 4.11V, which means the battery is charged to approximately 90%.
The head size of 33mm will fit Light Painting Brushes (Universal Connector) and Light Painting Paradise connectors, which means there is potential for creating light trails. The head diameter is too large for 29mm T8 tube based light painting systems. A diffuser was included in the package, which allows the light to be used for omni-directional lighting, though its not the best diffuser at diffusing (I prefer Convoy's plastic diffusers).
User Interface
The WK40 has a rotary brightness ring below the head with 4 brightness levels, and a single tail switch with full click for on/off and half click to change modes..
From 'white light modes' (default), a double half click enters strobe, and half click exits strobe back to constant. Unfortunately, strobe is alternating frequency.
A triple click from white light enters 'color modes'. Half click then cycles green>white>blue>red. Strobe can be entered/exited the same way. There is last mode memory for 'color modes'.
A triple click from 'color modes' enters 'flash modes'. Half click then cycles colourful infinite gradient>police flash (4Hz)>color changing flash (6Hz)>color changing slow flashing (2Hz). When in colorful infinite mode, the light colour fades through the spectrum on a 15 second cycle. A single half click saves the colour at that point in the cycle, and another half click goes back to gradient mode. Unfortunately there is no last mode memory for these mixed colours, so if you turn the light off, you can't access that colour when you next turn on the light. There is last mode memory for the gradient mode, which always starts at red.
To change brightness the head ring is rotated in steps from low>medium>high>turbo. Only the ring moves, the head and body stay in the same position relative to each other.
What do I think about this user interface?
The combination of brightness ring, tail switch, and last mode memory for white, colours, gradient, and flash modes is good. There are many features that need improving:
There is no last mode memory for mixed colours, or strobes. I would like to see all modes/colours memorised. Maybe instead of using the gradient mode to choose colours, color mode should have 10 preset colours (e.g. red, orange, yellow, lime, green, cyan, blue, magenta, pink, white) with double click moving between each colour?
Flash modes are generally too slow for light painting (though they may be useful for use with light wands for traffic management, but no light wand is included). An additional faster RGB flash mode (10Hz) would be more useful for light painting. An additional memorised fast gradient/colour fade mode (e.g. 3 second cycle) would be very useful for light painting.
Alternating frequency strobe is not useful for light painting. I would prefer a constant frequency strobe (10Hz).
Optics, Output, and Runtime
The Wurkkos WK40 uses a quad TIR optic, with the following LEDs:
LUMINUS SST20 white 6000-6500K - max 1000 lumens (3hr)
LUMINUS SST-20-DR-B120-V660 deep red - max 100 lumens (2hr10m)
LUMINUS SST-10-G-B130-E530 green - max 300 lumens (3h)
LUMINUS SST-10-B-B130-N450 blue - max 50 lumens (2h)
It needs to be noted that white and colour lumens are not directly comparable, and there are large differences between the efficiency of different colour LEDs. The brightness levels are well spaced, and the lowest brightness settings are approximately 1% of max output.
The quad optics works well for illumination purposes, with a relatively throwy beam for an RGBW light, 30 degree hotspot, and 160 degree spill beam. There is some beam artifact at close distance, but not a real world issue. For use in light painting connectors, the off-central axis LEDs mean that some of the light is attenuated before it reaches the light painting tool. This is more of an issue in the Light Painting Paradise adapters with 20mm aperture, than the Light Painting Brushes Universal Connector with 25mm aperture. However the light is perfectly useable with both of these systems. The quad optics also mean the colour mixing isn't great. A centrally positioned RGB or RGBW emitter within a single TIR optic (as per the RGB Critter) may be more optimal for light painting. However, there may be brightness tradeoffs with that design, so there may be good reason for quad optics in this light!
The choice of SST emitters is interesting. The white LED is a cool white SST20 6500k, with the standard low CRI. I would prefer the 95CRI CRI 4000k version, but the drop in max lumens would be less marketable. As usual with the SST-20 is an increasingly green tint at as brightness decreases. The 660nm red LED is deep red, instead of more common red 620-630nm orange-red. This is probably better for preserving night vision. The 450nm blue is the usual "forensic blue" (often shows as blue to purple in photos) and can make some fluorescent objects glow. The 530nm green is monochromatic, unlike the lovely full spectrum Osram CSLNM1.F1 green LED. As white light flashlights are in abundance, I would prefer an amber LED instead of white.
Maximum lumens of some other RGB or single colour emitter lights on green compared to the WK40 (all on 100% mode):
LED Lenser P7QC (? XML2 Color LEDs) -21%
KDLITKER triple color (XP-E2 LEDs) -33%
AOAM RGB Critter (Unknown LEDs) - 62%
Convoy S2+ (CSLNM1.F1 LED) +441% (note: this full spectrum green, so not directly comparable)
Runtime testing on green turbo mode (with fully charged included battery) showed the light to stay above 90% of max output for a whopping 4hr 10mins, until the light stepped down to low mode. On white light mode, the temperature regulation kicked in at 2 minutes, with brightness fluctating between 40-100% for a while (similar to Sofirn's "sawtooth" temperature regulation). Runtime until a further step-down to low was 4hr. In both tests the light never became too hot to touch, with good thermal mass and heat distribution.
I don't have the resources to test runtime and brightness in every setting, but the green and white turbo mode tests exceeded the runtime stated in the manual by more than 30%. Going by the runtimes in the manual for turbo vs high mode, it looks like white and blue will have a step-down from turbo to high, and green and red don't step down in turbo mode. The runtimes stated in the manual for low mode appear to be highly exaggerated - maybe a decimal place error in calculations?
I could not detect any PWM on any mode, even gradient mode!
Conclusion
Positives:
Good maximum brightness for an RGB(W) light.
Useful beam profile for illumination.
Good sustained brightness.
Good value for money.
Last mode memory for Red, Green, Blue, White, gradient, and flash modes.
Capable of colour mixing.
Compatible with Light Painting Brushes and Light Painting Paradise systems.
USB-C charging.
Good range of included accessories, including diffuser.
No visible PWM.
Negatives:
No last mode memory for strobes or mixed colours.
No fast colour fade/gradient mode.
Strobe is alternating frequency.
Flash modes are too slow for light painting (may be OK for use with traffic wands).
Poor colour mixing.
Charging terminated too early at 4.11V.
I would prefer a side clip and/or lanyard instead of 26350 tube.
I have to applaud Wurkkos for thinking outside of the box, with an interesting and well engineered RGBW light concept. The light has relatively good brightness for an RGBW light, with a useful beam profile. I like the brightness ring for brightness and tail switch for mode changing.
For light painting photography, the tail switch firmware/UI needs improving with all modes memorised, additional fast colour fade mode, and improvements to strobe and flash modes. An amber instead of white LED should also be considered. For hunting, there are more throwy single colour flashlights that would more suitable. For general purpose RGBW light use, the Wurkkos WK40 is the best and brightest general purpose RGB(W) flashlight I have tested, and I hope that Wurkkos are able to make the requested changes to make the light more useful.
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