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!

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.

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

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

Why hello new and different material

Nope, try again.

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?

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.

Ah, I was answering a question that you hadn’t asked :slight_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.

Good example, thanks.

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

New and improved, extra fluffy phosphor?

BINGO!

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

Yay! What were they used for? Current spreaders?

Exactly.

:smiley: :smiley: :smiley:

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

Weeding out correlation from causality is always a problem.