Boat LED light amp draw: what your lights cost the battery

The short answer. Perko’s Stealth LED all-round lights draw 0.1 amps. Its bulb combination lights draw 0.80 amps per compartment, and both compartments light at anchor. Over a 10-hour night that’s 1 amp-hour for the LED and 16 for the bulb light. Amps times hours gives you amp-hours. Add them up for every light.

You’ll need

• The amp or watt figure for each light, from the maker’s own page or sheet (the table below has ours)
• A rough idea of how many hours each light runs on a typical night
• The Battery bank size calculator and the Run time calculator
• Optional, to check the real number: Victron SmartShunt 500A

An anchor light runs all night, every night you’re out. On paper it’s a small load. With two 10-watt bulbs in it, it takes more out of the battery by morning than most people guess.

The math is simple. Get one number per light from the maker, multiply by hours, add it up. Here’s how.

How many amps do our nav lights draw?

These are the lights we sell, with the numbers Perko prints on each light’s own catalog page. All run on 12V.

Three notes before you use the table:

• The 1124’s amps aren’t listed here on purpose. Perko’s page prints “80 amps” per compartment, which can’t be right for a 10-watt bulb. Its watts match the 1184 and 1183, so expect about the same draw. Check yours with a meter or a shunt if it matters.
• The 1609 has a courtesy light that works in the folded-down position at the dock. Perko doesn’t list a separate draw for it, so it isn’t in our math.
• Sidelights and sternlights aren’t in this list. We don’t carry them yet. Read the figure off your own light’s spec sheet or label and add it the same way.

Why does a combination light count twice at anchor?

A combination light has two compartments in one head. Perko’s installation sheet for its 1123 and 1124 lights says the forward compartment is the masthead light, and both compartments light together for the all-round (anchor) light.

So at anchor, you pay for two bulbs: 2 x 0.80 A = 1.6 A. A Stealth LED all-round light pulls 0.1 A for the same job. That’s 16 times less current.

If you’re not sure which light your boat needs to show, start with Boat navigation lights: which lights your boat needs. To choose between a fold-down LED and a combination head, see Fold-down all-round and anchor lights: how to pick one.

How do I turn amps into amp-hours a night?

Amps tell you how hard a light pulls right now. Amp-hours tell you how much it takes out of the battery over time. The step between them is one multiplication.

1. Find the amps. Use the maker’s figure. If the maker lists only watts, divide watts by 12 for a rough 12V number. (Perko’s 1184 shows why it’s rough: 10 W divided by 12 is about 0.83 A, and Perko lists 0.80 A. Use the maker’s amps when they give them.)
2. Count the compartments that are on. At anchor, a combination light has both lit.
3. Pick the hours. Use your real night. We’ll use 10 hours at anchor as the example.
4. Multiply. Amps x hours = amp-hours.
5. Add every light that runs that night. That total goes into the calculators.

Worked out with Perko’s numbers, for 10 hours at anchor:

Underway is the same math with different hours. Say you run 4 hours home after dark with a Stealth LED all-round light: 0.1 A x 4 h = 0.4 Ah. With one 0.80 A compartment of a combination light on, the same 4 hours is 3.2 Ah.

What does that do over a week?

Spread it out and the gap grows. Seven nights on the hook:

• Stealth LED: 7 x 1 Ah = 7 Ah.
• 1184 or 1183 at anchor: 7 x 16 Ah = 112 Ah.

On a weekend boat with a good charge waiting at the dock, 16 Ah a night might not matter much. Anchor out for a week on solar and it does: that’s 105 Ah more to put back. If you’re keeping the bulb light, plan for it. If you’re swapping, the LED pays you back every night.

How do these numbers feed the calculators?

Battery bank size calculator. This one adds up your loads per day. Enter each light as amps and hours, next to the fridge, pumps and electronics. It turns the daily total into the battery size you need for the days you want between charges. Changing one anchor light from 16 Ah to 1 Ah can move that answer.

Run time calculator. This one works the other way. Give it your battery and the amps you pull, and it tells you how long you’ll last. Add your lights’ amps to the rest of what’s running at night to see if you’ll wake up with enough to start the day.

Not sure what everything else draws? A shunt monitor answers that. With the Victron SmartShunt 500A on the battery negative, switch one light on at a time and watch the amps change in the app. That’s your real number, wiring and all.

Do low-draw LEDs still need the right wire and fuse?

Turn the power off at the breaker or switch before you open anything up. Then, yes: a small draw doesn’t mean any wire will do. Nav lights often sit at the far end of the boat, on a long run up a pole or out to the bow, and voltage drop over that length is what dims a light.

Size the wire for the whole run, out and back, with the Wire gauge calculator. Put the light on its own fused circuit at your fuse block. Follow the fuse size in the light’s install sheet.

If you’re replacing an old light, it’s a good moment to check the connections too. Green, crusty ends at the base of a pole light add resistance, and resistance costs you light.

Does this guide fit your boat?

This applies if: – Your boat runs a 12V DC system. – You want a nightly amp-hour number for your nav and anchor lights. – You’re sizing a battery bank, or checking whether a light swap is worth it.

This doesn’t apply if: – Your boat runs 24V. The method is the same, but the amps on these pages are for 12V lights. – You need cabin, deck or underwater light numbers. Use each maker’s own sheet for those, then run the same math. – The job touches shore power or anything on the AC side. That goes to a licensed electrician.

Products in this guide

The full range is in Navigation and anchor lights. Rewiring an old masthead or all-round light? The Nav light refit kit puts a Perko combination light together with the cable and terminals for the job.

Bundles for this job: Nav light refit kit

Quick answers

How many amps does an LED anchor light draw? Perko lists its Stealth LED all-round lights at 0.1 amps on 12V. Over a 10-hour night, that’s 1 amp-hour. Other brands differ, so check the maker’s sheet for yours.

How many amp-hours does an anchor light use overnight? Multiply its amps by the hours it’s on. A Perko Stealth LED at 0.1 A for 10 hours uses 1 Ah. A Perko 1184 combination light with both compartments on uses 2 x 0.80 A x 10 h = 16 Ah.

Is switching to an LED anchor light worth it for the battery? On amp draw alone, yes. With Perko’s numbers, the LED uses one sixteenth of the combination light’s current at anchor. The more nights you anchor out, the more that adds up.

Can I work out amps from watts? Roughly. Divide watts by 12 on a 12V boat. It’s close, not exact: Perko’s 10 W bulb light is listed at 0.80 A, not 0.83 A. Use the maker’s amp figure when there is one.

Do I need a bigger battery for LED lights? Usually not for the lights themselves. Add their amp-hours to the rest of your loads in the Battery bank size calculator and let the total decide.

Sources

• Perko Fig. 1639, Stealth Series LED fold-down white all-round light: https://perko.com/catalog/navigation_lights_under_20_meters/815/electric_fold_down_mount_for_masthead_and_all-round_lights
• Perko Fig. 1636, Stealth Series LED fold-down white all-round light: https://www.perko.com/catalog/navigation_lights_under_20_meters/814/stealth_series_-_led_fold_down_white_all-round_light/
• Perko Fig. 1609, Stealth Series tower/arch mount LED folding all-round light: https://www.perko.com/catalog/navigation_lights_under_20_meters/817/stealth_series_-_tower_arch_mount_led_folding_white_all-round_light/
• Perko Fig. 1184, combination masthead and white all-round anchor light: https://www.perko.com/catalog/navigation_lights_under_20_meters/837/combination_masthead_and_white_all-round_anchor_light/
• Perko Fig. 1183, fixed mount combination masthead / white all-round light: https://www.perko.com/catalog/navigation_lights_under_20_meters/131/fixed_mount_combination_masthead___white_all-round_light/
• Perko Fig. 1123/1124, combination masthead and white all-round light: https://www.perko.com/catalog/navigation_lights_under_20_meters/121/combination_masthead_and_white_all-round_light/
• Perko Fig. 1123 & 1124 installation sheet (PDF): https://www.perko.com/images/catalog/pdf/Fig.%201123%20&1124%20Inst%20(USCG).pdf