XM-L2 brighter due to higher forward voltage?

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ryansoh3
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XM-L2 brighter due to higher forward voltage?

Over at the BLF collaboration sheet, I read that XM-L’s were great for single celled lights because li-ions can supply more voltage until linear or buck drivers went out of regulation. This was due to the lower Vf of XM-L’s compared to XM-L2’s.

However, XM-L2’s are known to be approximately 15-20% brighter at a given current.

Connecting the dots, I concluded that the reason why XM-L2’s are brighter was because of the higher power input, as observed by the higher forward voltage.

Any thoughts?

Cheers!

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DimBulb
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and power input determine lumen output, as I understand it.

A higher Vf @ a given If may indicate a higher semiconductor bulk resistivity. Vf is due to bulk resistivity and junction V drop and If.

PilotPTK
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Completely incorrect, unfortunately. XM-L2 is brighter because it’s newer technology that is more efficient. LED Luminous output is relative to Current and has very little to do with Vf.

Although XM-L2 is roughly 20% brighter at a given drive current, it is not 20% more efficient. The higher Vf eats into some of the efficiency gains.

Example:
XM-L 3.0A at 3.4V Gives 800 Lumens
XM-L2 3.0A at 3.6V Gives 960 Lumens

Hence, XM-L2 is 20% brighter at 3.0 Amps, but uses 5.8% more power because of the higher Vf.
Calculating further, XM-L2 is 88.88 Lumens per Watt while XM-L is 78.43 Lumens per Watt.
XM-L2 is roughly 13% more energy efficient.

PPtk

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bose301s
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Looking at the XM-L vs. the XM-L2 die what differences do you see? Your answer lies in the answer to that question.

PilotPTK
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Why hello new and different material

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bose301s
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PilotPTK wrote:
Why hello new and different material

Nope, try again.
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Aside from the SiC tech, I suppose the reduction of an internal bond wire could lead to higher bond-wire resistance… That would kick Vf up a bit..

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PilotPTK wrote:
Aside from the SiC tech, I suppose the reduction of an internal bond wire could lead to higher bond-wire resistance… That would kick Vf up a bit..

I wouldn’t doubt if going to 2 bond wires vs. 3 did cause the Vf to go up, but I am more talking about what increased brightness as opposed to what increased Vf.

What can you see on top of the XM-L die that you can’t see on the XM-L2?

ryansoh3
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PilotPTK wrote:
Completely incorrect, unfortunately. XM-L2 is brighter because it’s newer technology that is more efficient. LED Luminous output is relative to Current and has very little to do with Vf.

Although XM-L2 is roughly 20% brighter at a given drive current, it is not 20% more efficient. The higher Vf eats into some of the efficiency gains.

Example:
XM-L 3.0A at 3.4V Gives 800 Lumens
XM-L2 3.0A at 3.6V Gives 960 Lumens

Hence, XM-L2 is 20% brighter at 3.0 Amps, but uses 5.8% more power because of the higher Vf.
Calculating further, XM-L2 is 88.88 Lumens per Watt while XM-L is 78.43 Lumens per Watt.
XM-L2 is roughly 13% more energy efficient.

PPtk

Well, I do agree that the XM-L2 is more efficient, but there is a positive correlation between Vf and lumens as well, right?

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PilotPTK
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ryansoh3 wrote:
PilotPTK wrote:
Completely incorrect, unfortunately. XM-L2 is brighter because it’s newer technology that is more efficient. LED Luminous output is relative to Current and has very little to do with Vf.

Although XM-L2 is roughly 20% brighter at a given drive current, it is not 20% more efficient. The higher Vf eats into some of the efficiency gains.

Example:
XM-L 3.0A at 3.4V Gives 800 Lumens
XM-L2 3.0A at 3.6V Gives 960 Lumens

Hence, XM-L2 is 20% brighter at 3.0 Amps, but uses 5.8% more power because of the higher Vf.
Calculating further, XM-L2 is 88.88 Lumens per Watt while XM-L is 78.43 Lumens per Watt.
XM-L2 is roughly 13% more energy efficient.

PPtk

Well, I do agree that the XM-L2 is more efficient, but there is a positive correlation between Vf and lumens as well, right?

No, there isn’t. XP-G2 is a prime example. It has higher lumens per watt and a lower Vf than the original XP-G. Vf has correlations to current and to temperature.

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bose301s wrote:
PilotPTK wrote:
Aside from the SiC tech, I suppose the reduction of an internal bond wire could lead to higher bond-wire resistance… That would kick Vf up a bit..

I wouldn’t doubt if going to 2 bond wires vs. 3 did cause the Vf to go up, but I am more talking about what increased brightness as opposed to what increased Vf.

What can you see on top of the XM-L die that you can’t see on the XM-L2?

Ah, I was answering a question that you hadn’t asked Smile

Truthfully, I don’t have an XM-L2 handy at the moment, and I can’t think of anything off the top of my head.

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PilotPTK wrote:

No, there isn’t. XP-G2 is a prime example. It has higher lumens per watt and a lower Vf than the original XP-G. Vf has correlations to current and to temperature.

Good example, thanks.

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@bose: the strips of wires(?) over the XM-L block the light?

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PilotPTK
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New and improved, extra fluffy phosphor?

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ryansoh3 wrote:
@bose: the strips of wires(?) over the XM-L block the light?

BINGO!

Not the only thing but a major part of the increase, the single biggest.

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Yay! What were they used for? Current spreaders?

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ryansoh3 wrote:
Yay! What were they used for? Current spreaders?

Exactly.
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PilotPTK wrote:
New and improved, extra fluffy phosphor?
Big Smile Big Smile Big Smile

So that’s what improved the tint! Shoulda known…fluffy=warmth

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ryansoh3 wrote:
Well, I do agree that the XM-L2 is more efficient, but there is a positive correlation between Vf and lumens as well, right?

Weeding out correlation from causality is always a problem.
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On the XM-L2, what is the function of the wire on the right of the dome that is not touching the phosphor layer?

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AlexGT wrote:
On the XM-L2, what is the funcion of the wire on the right of the dome that is not touching the phosphor layer?

Willing to bet it’s the ESD protection, I actually don’t know so this is just a guess.
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So there is more than one way to take advantage of the increased efficiency. One is to use a boost buck driver and run the xml2 at 3A+. Another would be to run the xml2 at a lower current(2.6-2.7A) and realize the efficiency gain in run time keeping output more constant. Thus would allow continued use of 7135 based drivers without loss of time in regulation. Obvious stuff but might as well say it.

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Perhaps there will come out some small regulated drivers which are suitable for xml2 and variable like the 7135…I hope so.

DimBulb
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Werner wrote:
Perhaps there will come out some small regulated drivers which are suitable for xml2 and variable like the 7135…I hope so.

Entshuldigung sie bitte Smile
but I couldn’t find where this is variable
http://www.micro-bridge.com/data/add/amc7135.pdf
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I think he meant versatile or flexible. Easy to use, fills almost any needs..

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NightCrawl wrote:

I think he meant versatile or flexible. Easy to use, fills almost any needs..


Sehr gut. . .:)
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Jawoll!

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Werner wrote:
Perhaps there will come out some small regulated drivers which are suitable for xml2 and variable like the 7135…I hope so.

Yes, I hope so too.
Aber schnell…!

(We might get a really nice custom driver offered by lightmalls though)

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For example you can add some 7135 or remove some so you can adjust the max current also you can program up your custom firmware…this is really versatile and cheap…