For bare throw, the most important factors are lens diameter and LED die luminance (usually referred to as surface brightness) - and then of course all the losses and the measures to reduce them.
While the optics part is covered in other threads, I couldn't find much info on die luminance. Is there any list?
If not, maybe we could compile one.
One could try to deduce that from the specs, but the specified LED flux (lumen) includes light strayed within the LED, which does not contribute to throw, thus this method over-estimates luminance.
The best method seems to be Ra's proposal: Measure the LEDs beam intensity (maximum) with a lux meter at 1m distance, then divide that by the apparent(!) die size as seen from ahead.
Measuring apparent die size might not be that simple, so I measured some typical LEDs with 1-2 methods:
a) measuring the width using an 100x low-NA microscope with scale and subtracting the contact pads (not good for XP-G, since the apparent area isn't a square any more)
b) taking a close-up image from the LED and counting pixels.
With the two XR-Es I applied both, and the results were within 3%
Apparent die sizes:
XR-E EZ900: 2.07mm²
XR-E EZ1000: 2.76mm²
XP-G: 3.50mm²
For luminance in cd/mm² just divide your measured beam intensity (it's proper unit is candela (cd), equivalent to lux@1m) and divide it by that area.
For standard units (cd/m²) multiply by 1 000 000.
Maybe we can collect some...
EDIT: Since gathering that data currently doesn't go that well, I'll post some die emittance (lumen per mm²) data meanwhile that I derived from the specs.
Theoretically the luminance is the emittance divided by pi, but as I wrote above this doesn't account for emitter package internal stray light.
The XR-E EZ1000 is reported to perform slightly (1-2%) better than stated at 1A.
While the optics part is covered in other threads, I couldn't find much info on die luminance. Is there any list?
If not, maybe we could compile one.
One could try to deduce that from the specs, but the specified LED flux (lumen) includes light strayed within the LED, which does not contribute to throw, thus this method over-estimates luminance.
The best method seems to be Ra's proposal: Measure the LEDs beam intensity (maximum) with a lux meter at 1m distance, then divide that by the apparent(!) die size as seen from ahead.
Measuring apparent die size might not be that simple, so I measured some typical LEDs with 1-2 methods:
a) measuring the width using an 100x low-NA microscope with scale and subtracting the contact pads (not good for XP-G, since the apparent area isn't a square any more)
b) taking a close-up image from the LED and counting pixels.
With the two XR-Es I applied both, and the results were within 3%
Apparent die sizes:
XR-E EZ900: 2.07mm²
XR-E EZ1000: 2.76mm²
XP-G: 3.50mm²
For luminance in cd/mm² just divide your measured beam intensity (it's proper unit is candela (cd), equivalent to lux@1m) and divide it by that area.
For standard units (cd/m²) multiply by 1 000 000.
Maybe we can collect some...
EDIT: Since gathering that data currently doesn't go that well, I'll post some die emittance (lumen per mm²) data meanwhile that I derived from the specs.
Theoretically the luminance is the emittance divided by pi, but as I wrote above this doesn't account for emitter package internal stray light.
The XR-E EZ1000 is reported to perform slightly (1-2%) better than stated at 1A.
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