LED test / review – Osram OSTAR Projection Compact LE UW Q8WP – Black Flat's big brother, very high luminance at higher flux!

Big disadvantage of XP-G2 is that it's not factory undomed (tint issues after dedoming) and because of very high Vf (and often with large Vf variation between LEDs) light output starts to decrease almost immediately with single cells lights; this led can be driven with CC for a long time before output starts to fade.

I see your point. However this is not efficiency of the LED but rather the LED-driver combo.

Very low Vf makes linear drivers inefficient. But at the same time it enables use of very efficient buck drivers w/out falling out of regulation, leading to better overall flashlight efficiency than that of a high-Vf LED + linear.
Sadly, at higher cost. And even with 2 mm² LED currents get high enough to cause driver availability problems.

Yes, we need compact high-current buck & buck-boost drivers for 3V LEDs. Although it doesn’t really make much of a difference at high currents. At medium currents they start to make a lot of sense. The LD4 linear driver is a very good, cheap option at high-currents. It’s also rather compact.

Where someone sees disadvantages someone else sees advantage…

XP-G2 is still no 1 emitter in my single cell thrower builds (easy re flowing, easy de doming, easy centering, constant and very high lux performance, very reliable, imho the best and unbeatable led for single cell fet thrower lights).

Imho there is no big performance drop at all… Well it does happen because of DD or turbo mode of Fet driver with sagging 4.3-4,6A of current but that is nothing drastic comparing to XM or XP emitters in same configuration.

I absolutely love this driver. I mean the hardware features-size-price. But software doesn’t support e-switch. And is not open source, so I can’t customize it to my preferences.

Would it be a problem to make a ring with too large, rectangular, centre opening and then adding a plug to make the opening acentric?

According to Entwickler im Interview: Osram OSTAR Stage | Production Partner the glass lens on top of Ostar Stage LEDs exists only to protect bond wires. There’s air between it and the actual LED.
I assume Q8WP is the same. If that’s so, removal of glass will make it brighter than the Blackie.

It’s ar-coated on both sides though. So you might gain maybe 2%. Still, better than nothing. :+1:

It’s less than 1% output difference, not worth the risk since the glass is also bonded to the paths on the PCB and might rip them off.

For Q8WP I can confirm, you can remove the glass cover without damaging the bonding wires.

It happened to me accidentally as I used a center ring which not fitted properly to the LED. However the gain in flux is absolutely negligable and also the tint hasn't changed.

@Agro: I would not recommend this since such center rings are used to 'hold' the reflector at the desired place at the LED and have to withstand high forces of it. I would doing so only if the reflector is screwed in but in this case there is no need either.

I spotted a minor weirdness in the datasheet.
The peak output is not at cool temps. It’s not at 25°C. It’s higher.
Furthermore, the loss from heating up to 85°C is just 3%.

I’m not sure if we should believe this…if yes, we can expect it to have real-life performance quite close to this test.

Uh, what datasheet are you looking at…?
The highest output is at –40C, and that’s because that is where the graph ends.

My bad. I looked at LE CG Q8WP datasheet instead. :person_facepalming:

Here the diagram of the LE UW Q8WP (same sample tested earlier) for forward voltage and light flux depending on temperature Tj (in °C).

I put a lot effort to make the thermal resistance from emitter to heatsink as low as possible to avoid errors.

For the next upcoming emitter tests I will publish also diagrams / measurements like this.

The temperature dependent output is really great and new data you are giving us!

I wonder, would you see the same shape curve if you did the experiment at, say, 5A instead of 0.7A? We are getting into very interesting device physics; potentially separating the effects of high current and high temperature on output.

Maybe, but at the moment I'm not able to measure the temperature dependence at more than 3 W LED power. :(

I'm planning a lot more powerful Cool/heat setup for the future, but it's unclear when it would be ready. At this point I can only say - it's done when it's done...

koef3, could you overlay curves from manufacturer datasheet on that picture?

The data of the manufacturer are valid for 1,400 mA only - but I measured with 700 mA due to design of test setup.

I am not sure if there is a significant difference between these measurements so I would rather not overlay curves on this picture...

I did the test with 1,400 mA now, like the testing conditions in Osram's datasheet, including also overlay of curves from the datasheet.

In the datasheet the values are shown up to 120 °C Tj only, in my diagram up to 150 °C. The change in light flux shown in the datasheet matches very well, and the decrease of Vf is lower than stated in the datasheet. Very nice. :)

Thanks :slight_smile:
It looks like the curves change with current, though just slightly.