Put this in `~/.config/redshift.conf`

redshift.conf

; Global settings
[redshift]
temp-day=6500K
temp-night=3600
transition=1
;location-provider=geoclue2
location-provider=manual

; Solar elevation thresholds.
; By default, Redshift will use the current elevation of the sun to determine
; whether it is daytime, night or in transition (dawn/dusk). When the sun is
; above the degrees specified with elevation-high it is considered daytime and
; below elevation-low it is considered night.
;elevation-high=3
;elevation-low=-6

; Custom dawn/dusk intervals.
; Instead of using the solar elevation, the time intervals of dawn and dusk
; can be specified manually. The times must be specified as HH:MM in 24-hour
; format.
;dawn-time=6:00-7:45
;dusk-time=18:00-18:30

; Set the screen brightness. Default is 1.0.
;brightness=0.9
; It is also possible to use different settings for day and night
; since version 1.8.
brightness-day=0.8
brightness-night=0.65

; Set the screen gamma
;gamma=0.8
gamma-day=0.9:0.8:0.9
gamma-night=0.9

; The location provider and adjustment method settings
; are in their own sections.
; This is an example lat long for Portland, OR
[manual]
lat=6.2686594
lon=-75.7364816