When choosing a dimmable fixture for a particular application, it is important to be aware of the cost of the controls that will dim the fixture. On the market today, there are many LED fixtures that come standard with dimming. While having a fixture that dims may not increase the cost, adding dimming controls over switching will have an impact.
Most LED fixtures today are heading towards 0-10V dimming control. For electronic loads, this is the least problematic and consistent dimming method commonly used today. 0-10V dimming has the advantage that you don’t necessarily have to dim these fixtures. If the 0-10V wires are not connected to anything, the fixture is at full brightness – perfect for using the same fixture on a project with both dimming and switching applications.
Two-wire dimming is much more complicated at the fixture level for an electronic load. There are two types of two-wire dimming — forward and reverse phase. Forward phase dimmers are historically the most common dimmer; however, they are not necessarily compatible for all electronic loads. In general, electronic loads tend to function better with reverse phase dimming due to an in-rush of power to the electronics. Some electronic loads function well with forward phase, and some function better with reverse phase. The optimal dimming type for electronic loads can vary substantially for different dimmer/driver combinations.
For applications where emergency fixtures are to be dimmed and backed up by a generator or central inverter, NEC requires these controls to be overridden under loss of normal power. There are devices on the market to do this for both 0-10V and two-wire loads; however, the two-wire versions can be 2-3 times the cost of the 0-10V versions. Note that a control override device is required for each switch leg with emergency fixtures.
While additional wires are required for 0-10V loads, the dimming of these fixtures is more consistent and typically will be less expensive. Where two-wire dimming is necessary, we recommend that universal (forward and reverse phase) dimming controllers are utilized, and that these fixtures are not used for emergency egress lighting.