14 CFR § 25.1383

Each landing light must be approved, and must be installed so that—

No objectionable glare is visible to the pilot;

The pilot is not adversely affected by halation; and

It provides enough light for night landing.

Except when one switch is used for the lights of a multiple light installation at one location, there must be a separate switch for each light.

There must be a means to indicate to the pilots when the landing lights are extended.