We present a Mass-Luminosity Relation ( MLR ) for red dwarfs spanning a range of masses from 0.62 { \cal M } _ { \sun } to the end of the stellar main sequence at 0.08 { \cal M } _ { \sun } .
The relation is based on 47 stars for which dynamical masses have been determined , primarily using astrometric data from Fine Guidance Sensors ( FGS ) 3 and 1r , white-light interferometers on the Hubble Space Telescope ( HST ) , and radial velocity data from McDonald Observatory .
For our HST /FGS sample of 15 binaries , component mass errors range from 0.4 % to 4.0 % with a median error of 1.8 % .
With these and masses from other sources , we construct a V -band MLR for the lower main sequence with 47 stars , and a K -band MLR with 45 stars with fit residuals half of those of the V -band .

We use GJ 831 AB as an example , obtaining an absolute trigonometric parallax , \pi _ { abs } = 125.3 \pm 0.3 milliseconds of arc , with orbital elements yielding { \cal M } _ { A } = 0.270 \pm 0.004 { \cal M } _ { \sun } and { \cal M } _ { B } = 0.145 \pm 0.002 { \cal M } _ { \sun } .
The mass precision rivals that derived for eclipsing binaries .

A remaining major task is the interpretation of the intrinsic cosmic scatter in the observed MLR for low mass stars in terms of physical effects .
In the meantime , useful mass values can be estimated from the MLR for the ubiquitous red dwarfs that account for 75 % of all stars , with applications ranging from the characterization of exoplanet host stars to the contribution of red dwarfs to the mass of the Universe .