Official rule text as published in the U.S. Coast Guard Navigation Rules
The lights prescribed in Rules (Subpart C) shall have an intensity as specified in Annex I to these Rules (33 CFR part 84), so as to be visible at the following minimum ranges:
(a) In vessels of 50 meters or more in length: (i) a masthead light, 6 miles; (ii) a sidelight, 3 miles; (iii) a sternlight, 3 miles; (iv) a towing light, 3 miles; (v) a white, red, green or yellow all-round light, 3 miles; and (vi) a special flashing light, 2 miles.
(b) In vessels of 12 meters or more in length but less than 50 meters in length: (i) a masthead light, 5 miles; except that where the length of the vessel is less than 20 meters, 3 miles; (ii) a sidelight, 2 miles; (iii) a sternlight, 2 miles; (iv) a towing light, 2 miles; (v) a white, red, green or yellow all-round light, 2 miles; and (vi) a special flashing light, 2 miles.
(c) In vessels of less than 12 meters in length: (i) a masthead light, 2 miles; (ii) a sidelight, 1 mile; (iii) a sternlight, 2 miles; (iv) a towing light, 2 miles; (v) a white, red, green or yellow all-round light, 2 miles; and (vi) a special flashing light, 2 miles.
(d) In inconspicuous, partly submerged vessels or objects being towed: (i) a white all-round light; 3 miles.
Color note: black text applies generally; blue is International Waters; green is Inland Waters.
MyCOLREGS explanation
Summary
Rule 22 sets the minimum visibility ranges for each required light, scaled to vessel length. Presumably, the manufacturer of your boat knew that and added lights that meet these specs.
Real World Example
The ranges scale with vessel size because stopping distance and maneuvering room scale with it too - a large ship needs to identify a crossing situation miles out to have any real chance to act, while a small boat's shorter-range lights are calibrated to how quickly she herself can dodge. That gap is also why a fully compliant recreational sidelight can still go unnoticed from a ship's bridge until surprisingly late, even though both boats are entirely within the rules.
Practice Questions
Q1. The minimum distance for any light to be seen on the smallest size boat requiring side lights is:
A. 1 mile
B. 2 miles
C. 6 miles
D. there is no minimum
Q2. You buy a small hardware-store LED lantern to use as your boat's sidelight. Does simply having "a red light" and "a green light" showing satisfy Rule 22?
A. No boat under 20 feet needs to meet any range requirement, since Rule 22's visibility ranges only begin to apply at larger vessel-length brackets.
B. No - Rule 22 requires the prescribed lights to meet specified minimum visibility ranges (and Annex I intensity specs) based on vessel length, not just show the right color.
C. Yes, any red or green light qualifies as a sidelight, since Rule 22 only specifies color, leaving brightness and range up to the boat owner.
D. Yes, as long as the light is battery powered, since Rule 22's requirements were written for older vessels using less reliable lighting technology.