So what to do?

In their models they have Is and N. From these we can get Vf at a particular Vd very easily according to the relationship:

\(

I_f \; = \; I_s \cdot e^{ \( \frac{V_f}{N V_t} \)}

\)

Solving for Vf we get

\(

V_f \; = \; N V_t \cdot \ln \( \frac{I_f}{I_s} \)

\)

I used this to set up a little spreadsheet where I have sorted the list of stock LEDs based on the forward voltage at the specified average current and also added a column for the forward voltage at a specific current contained in another cell. The table is sorted in order of descending Vf@Iave. The following table uses If=20mA.

Part #|Mfg|Is (A)|N|Iave (A)|Vf@Iave (V)|Vd@If (V)

PT-121-B|Luminous|4.35E-07|8.37|20.000|3.84|2.34

NSCW100|Nichia|1.69E-08|9.626|0.030|3.60|3.50

NSPW500BS|Nichia|2.70E-10|6.79|0.030|3.27|3.20

LUW-W5AP|OSRAM|6.57E-08|7.267|2.000|3.26|2.39

AOT-2015|AOT|5.96E-10|6.222|0.180|3.16|2.80

W5AP-LZMZ-5K|Lumileds|3.50E-17|3.12|2.000|3.13|2.76

LXK2-PW14|Lumileds|3.50E-17|3.12|1.600|3.11|2.76

NSSWS108T|Nichia|1.13E-18|3.02|0.040|2.99|2.94

LXHL-BW02|Lumileds|4.50E-20|2.6|0.400|2.95|2.75

NSSW008CT-P|Nichia|2.30E-16|3.43|0.040|2.92|2.86

QTLP690C|Fairchild|1.00E-22|1.5|0.160|1.90|1.82

Note that this doesn't take into account some of the other model parameters such as Rs, but it gives a good starting point.

Hopefully this will be helpful to someone.