V5.1 builds on V5.0 and includes additional metrics around quality of light and controllability. The DLC goals for V5.1 are:
DLC - Goals of Version 5.1
Spectral Quality. The requirements now introduce Color Maintenance for qualification, improved Correlated Color Temperature consistency for a Premium designation, and set new efficacy allowances for great color, among other updates.
Light Distribution and Glare. The requirements address beam angle and add a Unified Glare Rating (UGR).
Dimmability is redefined as containing a dimmable driver. Or, as a light that can be dimmed by external control signal and is specified as dimmable.
You can review the full V5.1 Standards on the DLC site.
