2 = Inverse Square (More akin to real-world light calculation)
Initially dark (1) - If this is enabled, the entity will need to be triggered to work.
Naming the light will make it ignore its Appearance (style). To get around this, use Custom Appearance (pattern) instead (in particular, the linked page has pattern strings used by the preset appearance values).
The Custom Appearance (pattern) property allows you to enter a string of up to 63 letters from a to z, representing brightness. If you entered 'abcdefghihgfedcba' then the light would go from bright to dim and back again and then repeat. To use this feature, you must name the light.
There's a limit of 4 total lightmaps per face in the BSP format. This means there's a limit of 4 named lights in the same visual area (3 if there's also unnamed lights).
There's a limit of 31 named lights per map. This includes all light_* entities.
Light from a light_environment entity overrides lighting on entity models if the entities have line of sight to the sky (i.e. sky faces) from the reverse direction of the angles/angle+pitch values of that light_environment entity.
To block line of sight and have entities take lighting from the ground as normal, use brushes textured with black_HIDDEN on the bottom face, and SKIP on the other faces.
To bypass this effect altogether, use light_spot with "Is Sky" set to Yes instead of light_environment.
Tip: Pair light entities with light fixtures so that the light appear more lifelike instead of emanating out of thin air.