J120 front copy

Converting a J/120 to LED Lights 

led navigatlightAs many of you do long deliveries or long distance offshore races the goal has been to extend battery life without recharging or using a photovoltaic device to keep your batteries topped off. The two choices to make are to purchase more expensive batteries such as glass mat or larger batteries to make them last longer or reduce the amount of current draw on the 12 volt system. I have done the latter on my boat by converting to LED lighting. I have done most of this conversion by trial and error so I wanted to pass on what I have learned. I have been using these bulbs for about a year without problems so I thought it would be appropriate to share my ideas.

Its logical
The power consumption of my Northstar GPS is about 12 watts or 1 amp. Each navigation incandescent bulb uses 10 watts each or .83 amps per bulb so if you are sailing at night the power consumption does add up. 

Typical life with 
95 amp hours marine battery

Device Amps w/incandescent Amps w/Led's






Navigation Lights



Stern Light



2 Cabin Lights



Total Amp Hours



Total Hours of Charge



With two navigation lights and one stern lights this could add up to 40 watts. The red and green navigation LED's lights draw only .42 watts compared to the 10 watt bulb it replaces. The red and green lenses block about 70 percent of the light of the incandescent! The stern light draws 20 watts but it's LED replacement draws only 2.2 watts. Adding this together one can save over 37 watts in navigation lights alone. The interior LED bulb draws only .36 watts compared to the the 10 watt halogen light.   One can see how these numbers can add up to significant power savings. Another reason for replacing your incandescent bulbs is because the LED service life is at least 10 times as long. Finally if an incandescent bulb and an LED bulb have the same type and condition, and the incandescent bulbs take the same amount of power from fresh batteries, the output will probably appear roughly equally bright. But the incandescent one will fade more rapidly when the batteries weaken. The LED one will continue working for many times the amount of time that the incandescent one does. The expected life of a battery is measured in amp hours. A battery with a capacity of 1 amp-hour should be able to continuously supply a current of 1 amp to a load for exactly 1 hour, or 2 amps for 1/2 hour, or 1/3 amp for 3 hours, etc., before dropping to 10.5 volts. If a battery can supply 5 amps for 20 hours then it is called a 100 Amp Hour battery. 

Where to find these lamps
The only places I have found to supply these type of bulbs are found online. I have used two different venders, usually receiving the bulbs within a week and most of the time sooner. The first is http://www.superbrightleds.com . They have most of the bulbs that I found are needed. The other would be http://www.autolumination.com . Generally if you can not find what you need on one site you can find it on the other and I did read they also ship internationally.

ledfestoonImportant rules to follow

Before purchasing bulbs there are a few basic rules to follow. First for color navigation lights it is best to use a red LED color for the red lens, a green LED color for a green lens and a white Led light for the stern light. Second, whatever light you use it is important to remember that individual LED's point in only one direction, where incandescent point in 360 degrees so you must consider this when installing a replacement.  Third, because they are LED lights it is also important to know that the LED will work only with the polarity one way. In an example the festoon lights (in photo above) may be installed two ways but lights up only in one direction.

The specific bulbs I have used
I own an American produced J/120 hull #97 so I can only give recommendations for my setup. These fixtures may change for different hull numbers.  The bow navigation lights use a "festoon" style bulb as shown in the pictures above. The 42mm length bulb seems to be the closest size to the old one but probably the 44mm will fit. 


1156 Mounting Base

 led sternlight  ledr1157 90 white

Bulb mounted in stern light with cover off

How it looks before mounting

The stern light uses a 1157 base with two side tabs and two contacts on the bottom (see illustration above). You can see it is a 90 degree type bulb so the LED's are pointed out.

 ledoverhead light  Ledw incdst

Bulb mounted overhead interior 
fixture with LED bulb lit

The bulb on the left is the LED with the wire leads bent out and the bulb on the right is the halogen incandescent bulb taken out

For the interior lights I have used an Wedge Base bulb (194/168 type) and have bent the wire leads out to match the configuration of the red lens halogen incandescent bulb. This bulb seems to work best since the LED's  point into five different directions. I left in the white incandescent bulb in place since I will be most likely be using it with shore power or the engine running. 

Bulb model numbers and where to find them
These are the specific bulbs I ordered online.


Part Number

Web Page

Red Navigation Light 4211 LED Festoon bulb - select red (42mm length) Click Here
Green Navigation Light 4211 LED Festoon bulb - select green (42mm length) Click Here
Stern Navigation Light Right Angle 30 LED bulb - Select 1157 White Click Here
Overhead Interior Light RWLED-5 Wide Angle LED bulb 12 VDC 5-LED Wedge Base bulb (194/168 type) Click Here

Fortunately most of the marine bulb bases use standard automotive sizes so it should not be difficult to pick that size fits the application. For those of you that have perhaps another bulb base this is a helpful link that can help determine what it is: http://www.autolumination.com/bases_filaments.html  Hopefully this will help many of you get started.