Thanks for the testing. This looks like an interesting LED.
To calculate the luminance you just divide the measured intensity above the LED (in cd) by the light emitting surface area, correct? In your picture from above the lit LED it doesn’t look like the area around the die is significantly lit from the side-escaping light, though this could be hard to tell in the photo. So if you are not measuring the light coming from the side areas you don’t need to include those areas in your calculation.
In lots of the new flip chip design LEDs the phosphor to the side is excited and emits significant light upwards which increases the LES for the purposes of your calculation, but that doesn’t seem to be happening with this LED. So maybe the luminance is actually higher.
Examining the LES is harder than on other LEDs.
I wasn’t sure if I should add the side areas to the total LES. And yeah, I divide the intensity with the total LES (in mm²).
For almost all Flip Chip based emitters the LES is much bigger than of the actual die itself. If this Q8WP is used in reflectors, there would be also the light coming from the side used? I understand that the reflector ‘catches’ not only the light from above (head on) and also this side areas affects the luminance. I am not sure about this but I can’t know everything about this topic.
Edit: I guess that the radiating surface is stated in the datasheet because this LED is used in projection systems. Maybe only the light from top surface is needed for this purpose and the side light emissions doesn’t matter. Maybe the glass window is also there to ensure precisely delimited edges for such applications.
A reflector might catch the side light, but for your luminance calculation that might not be relevant. If that side light doesn’t light up a surface for your luxmeter to see during your measurement, you shouldn’t include that area in the calculation. For some LEDs the LES is not a simple plane and the luminance is not a constant over the surface which makes your method of calculating the luminance prone to errors.
Really the most direct measure of the thing we care about is the measured intensity in a flashlight with known reflector area. The flashlight beam center is sampling the luminance of just the center of the die and so all of the complications associated with the other LESs to the side of the die are avoided.
Okay, I should have listen to my feeling. (Which says that the side LES doesn’t matter in this case.)
Maybe I will correct the luminance chart. Just take some further measurements to be on the safe side. But the yellow-colored area on the bonding pad belongs to the LES, because it emits significant amounts of light, right?
Thanks for the test! I believe I was the one who found this LED (by clicking through all of Osrams datasheets at the time). The sample here was imported from China (Alibaba), maybe they get rejected LEDs?
Regarding the luminance: measuring Candela with a reflector might help to get ballpark figures.
It was always important for me to measure LEDs without optics, especially these of flashlights.There are also many errors that could occur and I know that some LED manufacturers doesn't use secondary optics for luminance measurements.
I take some measurements with a Revtronic (Nitefighter) F30B, with SMO reflector, same focus, same lens, same centering:
Q8WP: 744 lm @ 57600 cd (77 cd per lm)
XP-G2 R5 dd: 420 lm @ 43100 cd (103 cd per lm)
XP-L HI V3: 802 lm @ 45200 cd (56 cd per lm)
You can see that the Q8WP is not the best choice for throw, like shown in the first luminance chart. I'm not sure to change my results, because the direct comparison in same optics apparently confirms my luminance values...
Yeah, and also the Q8WP has a lower luminance. It is not bad and for most thrower it will be enough.
I will not change the results until there are really good reasons to do so. If the luminance results would be much higher (like in case of smaller calculated LES) the shown ‘real life’ results (in flashlight) wouldn’t fit together.
What was the current during these measurements? It looks like the Q8WP has the highest throw?
Edit: I guess the Q8WP should have close to double the throw of the XPL HI if the LES was near 2mm^2.
The draw current was in all three measurements 4.00 Amperes (lab power supply and measured with clamp meter). In general I look closely to get the absolutely same environment and measurement conditions also in case of repetitions. The 105c limits the max current.
The XP-G2 seems to be underdriven, but originally (in domed state) it was only bin R5. Without dome the flux is another measured 27 percent less so it equals more to Cree flux bin Q5 or R2. Against it the Q8WP is a lot more efficient!
Thanks for the test.
EasyB is correct that if your luxmeter is right in front of the LED, the area that should be used for the calculation is the front area, which would be 1.55*1.23 = 1.9065mm^2
You can see in the real world test in your flashlight that the Q8WP still gets higher cd than the G2.
However, since it also emits light to the sides (which then get collected by the reflector but don’t add to the intensity) you end up with a worse cd/lumen ratio.
If all you care about is throw, cd/lumen doesn’t really matter as long as it still has higher cd.
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Taking the front area of 1.9065mm^2, we can do 153.9/1.9065*3.23 = 260.73cd/mm^2 which is just slightly below the Black Flat but still better than any cree LED.
You can see this reflected in your real world test, the Q8WP gets 1.336 times higher intensity than the XP-G2.
At 260.7cd/mm^2 it is 1.321 times higher than the 197.3cd/mm^2 of the XP-G2 (as seen in your table).
I’m not exactly sure why your XP-L HI did better than the G2 in your real world test but worse in the cd/mm^2 table, probably because you used two different XP-G2s, but it is still the case that the Q8WP outperforms the XP-L HI in both the real world test and in the cd/mm^2 measurements, suggesting that the 260cd/mm^2 is correct.
Yeah, but only because of the bigger (side) LES and higher efficiency than the old shabby R5 XP-G2.
If I had used a dedomed XP-G2 S4 2B the intensity would be much higher than of the Q8WP, at approx 73 kcd or so - despite smaller LES because the XP-G2 doesn’t emit any light directly to the side.
Gradually I have the impression that the (also my) method to get the luminance is wrong. As far I understood the luminance depends on solid angle (Steradian), the light flux in this angle and the LES. If the brightness is measured and divided by the LES, we get such result that not depends on the angle of emitted light.
The next days I test another XP-G2, maybe in S2 bin. The dedomed XP-G2 S4 2B of my chart is broken and I am not sure about the by Hank newly discovered old XP-G2 S4 that they are as good as the old ones…
You’re right, the side light does seem to affect the emission profile a lot, especially at about 45 degrees, since it is very different from the no-dome black flat or synios LEDs.
I am still unsure of how putting this LED in the flashlight affected your lux readings though, since the reflector on a flashlight collects the side emission more than the forward emission of an LED.
I would suggest using a lens instead, to just take the front view and emission of the LED, maybe that will give more accurate comparison between LEDs.
It will also be easier to get a consistent lux reading since using a lens will give a nice uniform die projection rather than a spot with a corona.
Thanks for testing this led, it was on my list but you keep relieving my BLF-workload
Some thoughts.The light emitted to the side does hit the reflector but predominantly the deepest part that gives a much worse hotspot projection than near the edge of the reflector, and does not add much to the cd of the hotspot.
It is a matter of choice if you use a reflector or lens for testing throw, I assume the optimal emission profile for both is slightly different.
I updated the luminance values for all LEDs shown in test chart including Q8WP. After several 'real-life condition' measurements in flashlight optics (SMO reflector) this LED has a very high luminance at much higher light flux than Black Flat which makes it very interesting for ultra-long-range flashlights with more output!
To ensure more realistic values for 'real-life' conditions (flashlight use / secondary optics) I established a new testing method to determine the luminance with a SMO reflector. All upcoming and already existing tests will use this method!
Updating of my other tests will be done in the next hours / days.
At this point big thanks to everyone who helped me out to establish this new test method and answered my questions about this! :)
The Driver and Enderman will have to change their emitters now :laughing:
So we have excellent results here but with higher current draw… No I don’t wan’t it it in single cell light…
But if there would be good and reliable buck driver with 9.6A draw I would think about adding additional 18650 tube to my lets say special edition lights.
20% lux performance with larger die than old g2s42b is not a joke… And it is best looking emitter ever imho.
Well, my big thrower was designed for this LED, but it’s just too much work. I don’t want to wait for the light again, currently. Maybe, when higher Bins become available. I think Enderman told me about a slightly updated version of this LED a while ago which doesn’t have the lowest bin anymore.
There are good buck drivers for 9.6A, but they have a large diameter.
Because of the low Vf you could just use a LD4 linear driver. It’s compact, works very good and not too expensive!
Haha
I’m still gonna go with the CFT90 for the syniosbeam, 5000 lumens will still be pretty amazing.
As for throw, the black flat still is a bit better, especially since I don’t have any 10 amp buck drivers around.
