Here is my homemade Sunlike 3V flashlight. I got an existing cheap 1W lead acid battery powered flashlight with 80 CRI LED. I just thought of replacing it with Sunlike 6500K to have a high CRI flashlight.
Photometric data from my OPPLE G2 is 7612K @ -0.0084 dUV. The thing that confuses me is that a -0.0084 dUV Sunlike 6500K looks exactly like Actual Daylight from the window compared to a -0.005 or -0.006 Sunlike 6500K . A Sunlike 6500K at -0.005 to -0.006 dUV looks slightly “Yellow Green” compared to Actual Daylight.
20mm MCPCB is compatible with the reflector so all I need to do is just direct replacement. I reflowed two Sunlike 6500K side by side since this is a low power LED at 0.2W nominal and 0.5W maximum)
When you compare against daylight, what illuminated surface are you comparing on, and what is the composition of daylight (direct sunlight, overcast sunlight, blue sky, etc.)? I’m trying to figure out why the extremely low duv seems natural in comparison.
It is quite a royal pain to figure out an optical system that eliminates the multi emitter artifacts while maintaining efficient transmission.
the illuminated surface i am comparing is a white t-shirt. i used white t-shirt this time because both real sunlight and Sunlike have ability to generate blue-fluorescence from white fabric. if I am comparing Bridgelux Thrive to daylight, i would use white styrofoam to exclude blue fluorescence.
Regarding the daylight source, it is a indirect sunlight (overcast) coming from the window. it is mostly skylight with some slight reflection from concrete or vegetation. The actual daylight dUV in my home ranges from +0.005 up to +0.01. Even at +0.01 I really can’t see green tint from real sunlight, only white, bluish white or maybe to some extent bluish-greenish white.
the thing that makes comparing a headache is because of the “chromatic adaption” or “auto white balance” function of the human eye. So most of the time, I would get blind from the real tint of the light source and see it as neutral. The only way not to get blind sided is to compare two light sources side-by-side at the same time, and viewing them simultaneously using a light separator of some sort.
I think I got an explanation as to why a Sunlike 6500K with an extremely low duv (-0.0084) seems more closer to daylight compared to a Sunlike 6500K at -0.005. The thing that makes the Sunlike 6500K dUV -0.005 look a bit off from real daylight, is its “greenish tint”, but if you increase the “intensity” of light, this greenish tint sort of gets minimized. The Sunlike 6500K with -0.0084 has lower greenish tint and it actually looks like white with sort of light orange-yellow tint which to my eye looks more neutral and closer to daylight.
From my personal observation, Actual daylight 6500K is whiter and bluer than Sunlike at 7,200K to 7,400K at -0.0084 dUV (Sunlike actually looks more Yellow compared to daylight despite the higher CCT)
also Actual 5700K Sunlight at +0.01 dUV looks neutral-bluish white compared to 5600K Sunlike at -0.005 to -0.008 ( Sunlike actually looks Light Orange compared to real Sunlight at 5700K ).
Bridgelux Thrive at 6200K with -0.002 to -005 looks like Actual Sunlight at 5400K at +0001 to +0.01 dUV
(1) I am worried that the SunLike induces fluorescence to nowhere near the same amount compared to overcast daylight. Even compared to, say, the Optisolis, the SunLike has a lower violet spike. Furthermore, I wear photochromic lenses, which readily turn dark in daylight but does so much slower when illuminated by SunLike 5700K at point-blank range.
(2) It is possible that daylight is an ill-defined reference. Things like background (vegetation and concrete as you pointed out), cloud type, air quality, time of day, etc., can all significantly impact not just the duv but other aspects of the spectrum. Very cold daylight has a great proportion of its emission in the violet+UV range, which induces a significant change in spectrum due to fluorescence.
If you are lucky, you might be able to find some toilet paper or other white surface (check with UV light) that does not fluoresce.
I did a re-test today and I followed your suggestion using toiled paper but we don’t have one, so i used Kitchen paper towel. I tested it first to make sure there is No UV fluorescence by exposing it to Marktechopto 400nm LED. In my area, Daylight never goes 0.000 dUV it is usually +0.005 to +0.01 on average. occasionally, +0.002 and as high as +0.02 but it never goes zero or negative. I can usually get 6500K and higher around late 5:00PM or earlier than 6:00AM. Lightmaster G2 Pointed directly on the sky would get 6500K at +0.005. I’m not interested on lighting below 6000K because of poor color contrast, although it is more pleasing to the eye.
So here are my observation:
Sunlike 6500K ( 7612K at -0.0084 dUV ) - using a side by side reference daylight, to my eye, this looks like a daylight source at 5500K with +0.005 dUV. It is actually “orange-yellow” compared to an actual 7600K at +0.001 to +0.01 dUV which is bluer and whiter.
Sunlike 6500K at ( 7423K at -0.0060 dUV) - side by side comparison with actual daylight, to my eye, it actually looks like 5500K at +0.02 dUV daylight (yes we have an actual window light at +0.02 dUV) . This one looks “yellow-green” compared to an actual 7400K at +0.001 to +0.01 dUV daylight in which again is whiter and bluer.
From my observation, there is a difference in perception compared to what is being displayed by the instrument (lightmaster G2).
For Example: If we compared two light sources A and B. Light source B would appear yellow or orange compared to Light source A, even if B has higher CCT at 7400K. CCT alone can’t be the one that defines the yellow-blue property of a light source, dUV also affects the yellow-blue color of an LED. Likewise, a higher dUV would also make an opposite effect, shifting the color of the LED to be blue-green.
Light source A: 6500K at +0.001 dUV
Light source B: 7400K at -0.008 dUV
There is definitely something wrong with the equipment, since the SunLike seems 2000K warmer than the measuring device indicates. This is a point that I have previously overlooked–I remember seeing the same device testing a 519A and reading a CRI of 100, so its numbers are likely far from reliable for even higher CRI sources than 519A.
I would imagine the error to be particularly egregious toward the upper end of CCT, since as CCT goes up, it takes less perturbation (in fact, an arbitrarily small perturbation) to a spectrum (measured by Euclidean distance on the CIE 1931 diagram) to produce the same change in CCT.
either it’s the Lightmaster G2 tha’s wrong or it is my eye. The G2 suggest that the Sunlike 6500K is at 7000+K CCT and -006 to -0.008 dUV but my eye suggests that it is at 5400K - 5500K at +0.02 dUV .
today, i have an overcast rainy sky at 6200K +0.0027dUV. Sunlike 6500K measured by G2 at 7000+K with dUV -0.006 to -0.0084 still looks slightly yellowish greensih compared to overcast sky on white fabric target. But if I used a Kithen paper towel target (no uv fluorescence), overcast daylight and Sunlike looks very close it’s hard to tell which one is overcast daylight and which one is Sunlike.
I wonder if there are ways to detect whether/how the device fails to register the correct CCT/duv. Like starting with an incan or sunlight (reference spectrum) and adding blue to it and see how the CCT/duv/CRI changes. Or mixing daylight and SunLike and see if the combined spectrum has CCT/duv that measures between the two extremes.
Kitchen paper (no fluorescence) is a better target for these comparisons. As mentioned before, overcast daylight emits a lot more UV proportionally than SunLike-type LEDs (which were engineered to minimize UV to avoid damage in art galleries). I could have a room that is barely lit by daylight, and all the glow in the dark items would be glowing obviously.
Another interesting test is to get readings for direct sunlight/daylight, and then get the reading for daylight bounced off white fabric. This way you could tell how much fluorescence throws off the spectrum.
. A Sunlike 6500K at -0.005 to -0.006 dUV looks slightly “Yellow Green” compared to Actual Daylight.
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