Day Night cycle

In terms of daylight during the day/night cycle:

when dusk begins the light decreases until
evening (aka nighttime) which is full darkness until
morning which increases the light level until
dawn (aka daytime) which is full brightness until dusk

Defaults as follows: ticks_per_day=25000 (approx 6 mins 56.4 secs)
dusk=0.25, evening=0.45, morning=0.55, dawn=0.75

If you keep your numbers < 1 , it's the percentage
of the total ticks at which the phase of day will change
Not sure what happens if you go > 1

When setting these variables, the command will fail if it changes
the order of the phases. Ex: morning must be > evening but < dawn

Lastly, the map starts at time tick 0 so if you want to start during full
daylight you want a dusk > 0

See also: https://wiki.factorio.com/Game-day

Day/night cycle examples:

-- Vanilla
-- ~7 minute cycle, 3m28s of full light, 1m23s light to dark, 42s full dark, 1m23s dark to light
local day_night_cycle = {
    ['ticks_per_day'] = 25000,
    ['dusk'] = 0.25,
    ['evening'] = 0.45,
    ['morning'] = 0.55,
    ['dawn'] = 0.75
}

-- Bright
-- 10 minute cycle, 4m of full light, 4m light to dark, 6s full dark, 2m dark to light
local day_night_cycle = {
    ['ticks_per_day'] = 36000,
    ['dusk'] = 0.2,
    ['evening'] = 0.59,
    ['morning'] = 0.6,
    ['dawn'] = 0.8
}

-- Double length cycle
-- ~14 minute cycle, 6m56s of full light, 2m46s light to dark, 1m24s full dark, 2m46s dark to light
local day_night_cycle = {
    ['ticks_per_day'] = 50000,
    ['dusk'] = 0.25,
    ['evening'] = 0.45,
    ['morning'] = 0.55,
    ['dawn'] = 0.75
}

-- Gloomy
-- 10 minute cycle, 6s of full light, 2m light to dark, 4m full dark, 4m dark to light
local day_night_cycle = {
    ['ticks_per_day'] = 36000,
    ['dusk'] = 0,
    ['evening'] = 0.2,
    ['morning'] = 0.6,
    ['dawn'] = 0.99
}

-- Half-length cycle
-- ~3.5 minute cycle, 1m44s of full light, 42s light to dark, 21s full dark, 42s dark to light
local day_night_cycle = {
    ['ticks_per_day'] = 12500,
    ['dusk'] = 0.25,
    ['evening'] = 0.45,
    ['morning'] = 0.55,
    ['dawn'] = 0.75
}

-- Long days, long nights, fast transitions
-- 20 minute cycle, 9m of full light, 1m light to dark, 9m full dark, 1m dark to light
local day_night_cycle = {
    ['ticks_per_day'] = 72000,
    ['dusk'] = 0.225,
    ['evening'] = 0.275,
    ['morning'] = 0.725,
    ['dawn'] = 0.775
}