Domeless SST90?

From what I've read on these forums, "dedoming" the SST90 results in significantly more throw (but less lumens) when used with a reflector. It makes sense since the angular radiation pattern is wider causing more of the light to hit the reflector.

What seems strange to me is that none of the larger manufacturers are using dome-less 90s, including dedicated throwers such as the SR-90. Why is this? Is it because they are trying to strike a balance between throw and lumens?

The Luminus nomenclature for a domeless from the factory is CBT-90. When I search this product, the total lumens (binning) is much, much lower than the SST-90 options. I know that dedoming does reduce the total output somewhat, but changes this large seem to indicate that the higher bins are not available in the CBT-90 series. Does anyone have insight into this?

In reading throw various CPF threads, it seems like manually removing the dome from a SST-90 is a bad idea. Sounds like the chance of damaging the LED is quite high. Plus some people say that there is some type of gel between the LED and dome and removing this significantly reduces the lifespan of the LED. What are you opinions/experiences with manual de-doming?

Thanks

nc_hooper said:

What seems strange to me is that none of the larger manufacturers are using dome-less 90s, including dedicated throwers such as the SR-90. Why is this? Is it because they are trying to strike a balance between throw and lumens?

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I'm not a manufacturer, but I suspect that it's because of the relative rarity of the domeless versions, and as you've noted the throw vs lumens issue. Might sound more impressive to have a higher lumen figure than stating the intensity.

nc_hooper said:

The Luminus nomenclature for a domeless from the factory is CBT-90. When I search this product, the total lumens (binning) is much, much lower than the SST-90 options. I know that dedoming does reduce the total output somewhat, but changes this large seem to indicate that the higher bins are not available in the CBT-90 series. Does anyone have insight into this?

Click to expand...

Just a small side note, the CBT is on a copper base, while the SBT is on the same ceramic substrate as the SST. This improvement in thermal resistance is reflected in the CBT generally having higher output than the SBT. With that said, the changes seem about right to me, given the total internal reflection at the air:glass interface, a flat surface would reflect a fair amount. When that gets reabsorbed and heats up the die even further, I can see it reducing the efficiency of the SBT even further, although by how much I'm not certain. It may be that they're putting the better dice into the more popular SST-90s instead, but I wouldn't be able to comment on that.

Th232,

Thanks for your insight. Seems like the somewhat unknown is whether or not they are putting better dice into there more popular SST-90 products.

Sorry about the CBT, I meant to say SBT. But that brings up another question. From the person doing my flashlight build, they state that my given driver (in this case Der Wichtel 9 amp) regulates through the positive side of the driver and therefore the emitter needs to be electrically isolated from the heatsink. If this is the case, could I still use a CBT or do I need the ceramic substrate of the SBT?

Thanks again

http://www.luminus.com/news/12-15-11 CBT-90 Brightness Incr Annc.pdf

CBT-90 just got a bump up to SST90 levels. Hopefully they'll make it to the distributors in a couple months.

nc_hooper said:

Sorry about the CBT, I meant to say SBT. But that brings up another question. From the person doing my flashlight build, they state that my given driver (in this case Der Wichtel 9 amp) regulates through the positive side of the driver and therefore the emitter needs to be electrically isolated from the heatsink. If this is the case, could I still use a CBT or do I need the ceramic substrate of the SBT?

Click to expand...

That's a good question. From the electrical diagram on page 15 I would say no, but then I haven't played around with the CBT-90 much. The one time I had to email Luminus they answered my question fairly quickly, so I'd say it'd be best to ask them directly?

deadrx7conv said:

http://www.luminus.com/news/12-15-11 CBT-90 Brightness Incr Annc.pdf

CBT-90 just got a bump up to SST90 levels. Hopefully they'll make it to the distributors in a couple months.

Click to expand...

Just looked that up - that is good news and confirms that before the CBT-90 and SBT-90 where using lower flux bins. Just looked up the specs on the SBT-90 - they seem unchanged for now.

Th232 said:

That's a good question. From the electrical diagram on page 15 I would say no, but then I haven't played around with the CBT-90 much. The one time I had to email Luminus they answered my question fairly quickly, so I'd say it'd be best to ask them directly?

Click to expand...

From what I've read on CPF, people prefer the CBT-90 over the SBT-90 because the cooper give a better thermal path and so the LED can be driven harder. But I wonder how the people are mounting the CBT-90 into their flashlights. It seems like the large board with the uncentered LED would be difficult to place, and not possible to place on a heat sink post. So for me the SBR-90 (which is the SBT-90 mounted on a 20 mm star) seems to be more workable. However the higher flux bins recently announced for the CBT-90 don't seem to have made it to the SBT-90.

I've seen several people cut down the board to just what you need (ma_sha1 comes to mind?), since you really don't need the thermistor and the huge lugs. Centring it shouldn't be that much of an issue either since the die is right between the holes (page 16 of the datasheet). On a 20 mm star, centre to centre distance between two opposite holes is 19 mm, while on the CBT it's 18 mm, so with some judicious cutting you should be able to do it. I'm not sure exactly what your build is, but as long as there's enough space vertically, I think it could be done.

Regarding cutting down the CBT board, would there still be sodder points to attached the wires from the driver? The second question is whether the CBT can be electrically isolated from my heatsink. The person doing my build says that my 9 amp Der Witchtel driver regulates through the positive side of the driver and therefore needs to be isolated. I have already purchased a SSR-90 (a SST-90 on a 20mm star board) for this purpose but I'm always up for new ideas. The thermal characteristics and increase throw potential of the CBT-90 sounds very interesting.

The heat sync is a large aluminum piece going into a mag-D-like host. Plan to have lathed a short 18mm post for the LED.