Standing lamp

Illumination area

Standing lamps light areas to 50% in a "7 tile" radius circle, then lighting fades rapidly, as shown in the image below.

The white area (7 tiles out) is 50% illumination, required for best surgery success chance; the yellow (8-9 tiles) represents 30% or better, adequate for all general labor, avoiding mood penalties, and for growing decorative plants indoors in plant pots.

Note that 50% illumination is the maximum available for this kind of lamp, no matter how many are used. Only the sun or the sun lamp give "Brightly lit" (100%), necessary for most plant growth, but pawns are perfectly fine with "Lit" (30%) or better.

Visual representation

Also, the lighting that can be seen represented by in-game visual differences does not always correspond to the actual % of light on a tile. Also note that areas that are not in direct line of sight with a lamp can be quite well lit.

Line of sight is not always a limitation with light sources.

In the image above, the entire corridor is fully lit at 50%, even though the lamps are not in direct line with each tile. However, the tiles diagonally above the lamps, on the other side of walls, are in total darkness, whereas they appear to be partially lit in the screenshot.

Colored lights

There are three varieties of colored light: red, blue and green. The functionally is similar to the regular standing lamp but an aesthetic variant. However while the colored lights affect the brightness of tiles in same radius as the regular standing lamp, they are slightly less bright meaning tiles are only considered "lit" within 7 tiles of a colored lamp, instead of the 9 of the regular lamp.

By using colored lights near each other, you can combine the colors.

Using multiple lamps close to each other also gives the appearance of "white light" and a more well-lit area, though this has no actual effect in-game.

Light % is not additive above the maximum that single colored lights provide.

Combining different colored lights for a "rainbow" feel to your colony.
Screenshot courtesy of reddit user 'i_cant_even_english'.

Styles

Ideoligions allow the selection of styles which then change the texture of the certain items and buildings when constructed by the colony. These style variants can be crafted if the colony has the selected style, or can be looted from raiders from factions with the requisite style.