Quick answer: Choose boat LED lights by their job, then match the fixture to its water exposure and electrical supply. Plan navigation and anchor lighting separately from deck, cabin and underwater lighting.
This guide covers fixture selection, the navigation-light distinctions that affect a purchase, and a worked cable-loss calculation. Use the LED lighting calculator hub for broader planning; the example below focuses on voltage drop in a low-voltage lighting circuit.
Choose lights for the job they need to do
Start with the activity or signal you need, rather than buying the same strip for every location. According to USCG Rule 20(b), navigation-light requirements apply from sunset to sunrise, and other lights shown during that time must not be mistaken for the required lights, impair their visibility or distinctive character, or interfere with the look-out. Apply that restriction when planning decorative lighting. USCG Navigation Rules, Rule 20(b)
| Intended job | Selection priority |
|---|---|
| Navigation | Required colour, viewing arc and visibility range for the vessel and applicable rules |
| Anchor | The prescribed white-light arrangement for the vessel at anchor |
| Deck, cockpit or docking tasks | Put light on the working area and assess its effect on the required navigation lights |
| Cabin | Choose the output and controls around reading, moving about or general illumination |
| Under-gunnel strips | Choose the strip and its connections for the intended water exposure |
| Underwater accents | Match the fixture's documented immersion conditions to its proposed position |
Treat this as a purchasing checklist. A decorative colour option does not answer the navigation questions in the first row, and a fixture described for deck use does not establish its suitability for continuous immersion.
What navigation and anchor lights must show
Select navigation lights by their prescribed signal, not just their apparent brightness. According to USCG Annex I, navigation-light chromaticity must conform to specified colour boundaries; red, green and white are regulated colours in this application. USCG Navigation Rules, Annex I section 7
According to USCG Rule 21, the following colours and horizontal viewing arcs define the lights. Each row links to the relevant rule so you can distinguish a sidelight from a masthead, stern or all-round light.
| Light | Colour and viewing arc | Source |
|---|---|---|
| Starboard sidelight | Green, 112.5° | USCG Rule 21(b) |
| Port sidelight | Red, 112.5° | USCG Rule 21(b) |
| Masthead light | White, 225°, over the fore-and-aft centreline (as nearly as practicable on vessels under 12 m under the Inland rule) | USCG Rule 21(a) |
| Sternlight | White, 135° | USCG Rule 21(c) |
| All-round light | 360°; colour depends on its prescribed use | USCG Rule 21(e) |
According to USCG International Rule 22(c), vessels under 12 m require minimum visibility of 2 miles for masthead, stern and all-round lights, and 1 mile for sidelights. These figures describe the International rule; they are not presented here as separately verified Inland requirements. USCG Navigation Rules, International Rule 22(c)
For a power-driven vessel under 12 m, International Rule 23(d) permits an all-round white light and sidelights instead of the arrangement in that rule's paragraph (a). This is a defined alternative for that vessel category, not a reason to replace every prescribed light with a white strip. USCG Navigation Rules, International Rule 23(d)
At anchor, Rule 30(b) permits a vessel under 50 m to use a single all-round white light where it can best be seen instead of the fore-and-aft lights described in paragraph (a). An anchor light therefore does not mean a lamp attached to the anchor itself. USCG Navigation Rules, Rule 30(a)–(b)
Match water protection and materials to the location
For underwater lighting, choose by the stated immersion conditions. According to Wikipedia's IP-code reference, IP67 means dust-tight protection and an immersion test up to 1 m for 30 minutes; IP68 covers continuous immersion under conditions specified by the manufacturer. IP68 does not supply a universal depth or duration. Wikipedia, IP code
That distinction makes the buying decision concrete: compare the proposed mounting depth and immersion use with the documented conditions for the fixture. Do not treat a temporary immersion test as a promise about an underwater installation.
For strips, include the connections in that assessment. According to Wikipedia's LED-strip reference, coated strips can carry IP65 or IP67 ratings, or IP68 with suitable sealed connections, while uncoated tape has no water-ingress resistance. Buying coated tape alone does not settle how the completed strip assembly will be protected. Wikipedia, LED strip light
For saltwater use, also compare housing and fastener materials. According to Wikipedia's galvanic-corrosion reference, dissimilar metals in salt water can corrode galvanically, including aluminium in contact with stainless steel. An ingress rating answers a different question from the compatibility of those materials. Wikipedia, galvanic corrosion
Calculate voltage drop before choosing the cable
Use the circuit's current and full outgoing-and-return cable path. According to Wikipedia's voltage-drop reference, conductor losses dissipate energy as heat, and excessive drop can accompany overheating of wires and connections. Wikipedia, voltage drop
The voltage-drop calculator takes a one-way distance and doubles it internally. Its calculation is:
Circuit resistance = resistance per 1,000 ft ÷ 1,000 × one-way length × 2.
Voltage drop = current × circuit resistance; percentage drop = voltage drop ÷ supply voltage × 100.
Worked example with assumed inputs
Assumed inputs: a 12 V supply, a 5 A lighting load, and a 20 ft one-way run using 14 AWG copper. Use the calculator's planning figure of 2.525 Ω per 1,000 ft for that conductor; it is a calculator input constant, not a marine installation approval.
- Round-trip length = 20 × 2 = 40 ft.
- Resistance per foot = 2.525 ÷ 1,000 = 0.002525 Ω/ft.
- Circuit resistance = 0.002525 × 40 = 0.101 Ω.
- Voltage drop = 5 × 0.101 = 0.505 V.
- Percentage drop = (0.505 ÷ 12) × 100 = 0.0420833… × 100 = 4.20833…%, rounded to 4.2%.
- Voltage at the load = 12 − 0.505 = 11.495 V.
- Cable power loss = current² × resistance = 5 × 5 × 0.101 = 25 × 0.101 = 2.525 W.
The result exceeds the calculator's default 3% planning threshold. That threshold is a site setting, not a cited marine wiring standard. This calculation estimates cable loss for the assumed current; it does not establish the correct fuse, installation ampacity or fixture operating range.
Plan the installation around the complete circuit
Resolve the fixture's supply requirements, cable route and environmental protection before mounting it. The example above gives 11.495 V at the load from an assumed 12 V supply: matching only the nominal supply label leaves the cable loss unaccounted for.
Use this checklist to turn the selection into an installation plan:
- Compare the fixture's permitted input range with the supply and the calculated voltage at the fixture.
- Evaluate cable sizing and circuit protection together; do not select a fuse from the voltage-drop result alone.
- Include cable entries, strip ends and connectors in the water-exposure assessment.
- Review housing and mounting hardware as a material combination.
- Assess deck and decorative lighting alongside the required navigation-light arrangement before using them together at night.
Keep mains-powered equipment outside this low-voltage example. If the work involves shore-power mains wiring or a mains-powered driver, use a qualified electrician.
FAQ
Can I use coloured LED lights on my boat at night?
According to USCG Rule 20(b), additional lights must not be mistaken for the prescribed navigation lights, impair their visibility or distinctive character, or interfere with the look-out. A colour alone does not establish that an installation meets those conditions. USCG Navigation Rules, Rule 20(b)
Which side gets the red navigation light?
According to USCG Rule 21(b), red is port and green is starboard; each sidelight covers 112.5°. These are defined navigation signals, so do not select their colours as an aesthetic preference. USCG Navigation Rules, Rule 21(b)
Is an anchor light mounted on the anchor?
No. Rule 30(b) permits a vessel under 50 m to show a single all-round white light where it can best be seen instead of the arrangement in paragraph (a). USCG Navigation Rules, Rule 30(b)
Is IP68 enough to choose an underwater boat light?
The rating alone does not tell you the permitted installation depth. According to Wikipedia's IP-code reference, IP68 immersion conditions are specified by the manufacturer, so compare those conditions with the planned use. Wikipedia, IP code
Does a low voltage-drop result prove the wiring is suitable?
No. The worked example calculates voltage loss from assumed current, length and conductor resistance; it does not determine marine installation requirements or circuit protection. Use the result as one input to the complete circuit design.
Jack Shi
Founder & editor, LEDaskJack Shi builds and writes LEDask, an independent LED-lighting tools project operated by clooms. He designs the calculators, checks their formulas and reference values against published engineering data, and writes the guides across the site.
