Using Your Light Keeper Pro

One of the most valuable tools in the extreme decorators tool-kit is a mini-light tester.  While you can spend up to hundreds of dollars on some testers, the "Light Keeper Pro" (the 'LKP') is by far the best value.  At less than $20 it's a device you can't afford NOT to have!

Unfortunately the instructions that come with the device, as well as the video on the company website, lead you to believe that the LKP is a magical device that fixes lights faster than you can say 'Ho Ho Ho'.  The truth is that using the LKP does take some practice.  The good news is that you should be able to master it within a few minutes.

Many of the hints and tips in this article apply to any proximity light tester, including the inexpensive stick version.  The LKP is a bit more sensitive, but both types work exactly the same way.

In this article:

Information on the Light Keeper Pro

The LKP excels at fixing standard 'mini-style' holiday lights.  The LKP however won't work on LED (Light emitting diode) sets, C7/C9 or other large size screw-in type bulbs.  You should never use the 'trigger' function on any chaser type set (IE, one that has a control box on the set to create patterns and chase effects), or while still hooked up to a computer based animation controller (like Light-O-Rama or Animated Lighting).  Using the LKP in any of these situations could lead to destruction of the set or controller (more on that later).

The LKP as 2 main functions to detect and fix light sets:  The 'Trigger' function, and the 'Detector' function.  Before we can discuss how each works, we need to learn how mini-lights work, and some basic troubleshooting skills.

The Light Keeper Pro

Mini-Light Wiring


The first thing we need to understand is the difference between wiring things 'in parallel' versus 'in series'.

Generally, C7/C9 sets are wired in parallel.  That is, the bulb sits between the hot and neutral of the set.  Since each bulb has it's own path - from the hot, through the bulb, to the neutral - if one fails, the others remain lit. 

Lights in Parallel (picture courtesy 'How Stuff Works')

Mini lights on the other hand are wired in series.  Power comes in on the hot, goes through the bulb, and then out and into the NEXT bulb.  Only after a set number of bulbs, typically 35 or 50, does the set connect to the neutral.  If any bulb in this SERIES (see how that works?) of bulbs fails, the entire 35 or 50 lights go out. 

Mini-lights in Series (picture courtesy 'How Stuff Works')

In an effort to keep the set lit when a bulb burns out, the bulbs themselves have a built in 'shunt'.  The object of this shunt is to conduct the power through the bulb when the filament (the device that actually produces the light you see) breaks.  The shunt is coated in a insulating material that burns off when the filament breaks, preventing a dead short.

Mini-Light Shunt (picture courtesy 'How Stuff Works')

Grab any set of mini lights that have more than 50 bulbs, and what you will find out is that you actually have 2 or more sets of lights. For example, a 100 count set is usually made up of two 50 count sets wired together.  When repairing a set, you should consider each section as a separate set.

This 150 light set is actually 3 50 light sections (picture courtesy 'How Stuff Works')

Basic Troubleshooting

Before you jump in and start ripping lights down, do a bit of troubleshooting first.

1 - Are all the lights out that are plugged into a single household socket?  If so, then the problem is most likely not the lights - it's the breaker or GFCI (ground fault circuit interrupter)! 

2 - Do you have sets plugged in end-to-end?  If so, trace from the wall socket out toward the first set that is not lit.  Are all the sets after that first one out as well?  If so, you have most likely overloaded that first out set, causing the fuses to burn out. Typically, you shouldn't have more than 3 sets plugged in end-to-end.  Stacking more than 3 plugs is OK, just don't connect more than 3 END TO END.  Disconnect some sets, then replace the fuses in that first set that was out.

3 - Are both halves of a single set out?  First quickly check that the fuses have not blown by plugging another set into the END (not by stacking the plugs).  If the test set lights, you have at least 2 bad bulbs (1 in each section).  If it doesn't, replace the fuses.

4 - Have you had a cascade failure?  Since mini-light sets are wired in series, each bulb produces a fixed voltage drop.  In typical 100 count light strands there are 2 separate 50 bulb sections.  For the USA that means every bulb is made to drop (use up) 2.5 volts of our normal household current.  When a bulb burns out, and the shunt kicks in, the rest of the bulbs in that section must absorb the additional voltage.  For a few burnt out bulbs, this is no big deal as the extra voltage is spread out over multiple bulbs.  However, as more and more bulbs burn out, the voltage goes higher and higher.  Eventually you will get to the point where there is so much voltage that the remaining lights all burn out in a cascade.  Cascade failures are rare, but do occur.  If no amount of testing and replacing bulbs helps, take a good look at the remaining bulbs.  If they all have a black ring/soot inside the bulb, just throw the set away and replace it with a new one.

If you've done all the basic troubleshooting and you still have a section out, chances are you have a shunt that failed or failed to burn off its insulation properly.  This is the most common failure.

Using the trigger:

Contrary to the package and the video on the company website, the trigger does NOT fix every set with just a few clicks.  Based on my personal experience, the trigger only fixes sets about 10 percent of the time.  I typically skip it, but you can give it a try if you like.

First, be absolutely sure that the set you are trying to use the trigger on is NOT a chasing set (one with a control box), or hooked up to an animation (computer) controller.  The trigger actually sends a high voltage spark through the set in an effort to get the shut working.  This spark may damage controllers, and it's better to be safe than sorry. 

Unplug any sets that may be plugged into this one, either plug stacked or end-to-end. 

Remove any bulb from the section that is out, and insert the socket into the LKP.  Be sure that the metal tabs on the LKP line up with the metal tabs inside the socket.  If the set lights up at this point, congrats!  In a 1 in 50 chance you picked the bulb that was causing the problem.  Replace it and you are all set.
Otherwise, rapidly pull the trigger until you hear a click.  Do this up to 20 times.  If the set lights, great!  Remove the socket from the LKP, and replace the bulb you took out.

Otherwise replace the bulb and move on to the detector section.

Using the Detector Function

The single greatest thing about the LKP is the detector function.  Once you have practiced with the device a few times, you can quickly find the bad bulb and replace it.  Typically it takes me about 20 to 30 seconds to find the bad bulb using the detector function.  Unlike the trigger function, you can also use the detector on chasing sets or computer controlled sets without fear of harming them. 

Before you start, there are some special cases you need to know about:

Icicle Lights:
Be aware that some icicle light sets are not wired logically.  Normally you would expect that the bottom bulb in a drop connects to the top-most bulb in the next drop.  That is not always the case.  If at any point you are being frustrated by your icicle lights, go to the last bulb that DOES cause the LKP to beep and then un-twist the wires.  Follow the wire out of the socket that beeped into the NEXT socket.  You may find that the next socket is not the one you expect.

Lights on metal (wire-frames, clipped to gutters/aluminum siding, etc):
The LKP works by detecting minute amounts of magnetism that occur when electricity flows through wires.  When lights are near metal objects, like wire-frames or your home's gutters/etc, that metal can amplify that magnetism and cause the LKP to beep EVERYWHERE!  The only solution is to remove the light and socket from the metal and get it far enough away to get a true reading.

Blinker (red tip) bulbs:
If you use blinker bulbs, the clear bulbs with red tips, replace them with regular bulbs before testing with the LKP.  You can replace them when you finish fixing your set.

Chaser sets:
There are a couple of things you need to remember/do if you are trying to repair a chaser set.  Most important is to set the chaser function so the lights are ALWAYS ON (sometimes called 'solid').  It is impossible to use the LKP to fix a set when the bulbs are blinking/chasing.

Typically, chaser sets consist of four 35 count light sets that are twisted together (for a total of 140 lights per set).  That means every 4'th bulb is part of the same set.  Therefore you should test every 4'th bulb with the LKP instead of every bulb.  For example, you may have a set that is red, blue, green, yellow.  This sequence then repeats until the end of the set.

To perform the 'First bulb check' (step 2 from above), check the first bulb that is OUT.  If the yellow set is out, the first bulb check should be done at the first YELLOW bulb (which is actually bulb #4).

To fix the set, stick to ONE color and fix that one before proceeding to the next color. Let's assume that the red and green 'sets' are out. First fix the RED set by checking bulbs 1,5,9,13.... all the way to the end (if needed).  Once the red set is fixed, fix the green set by checking bulbs 3,7,11,15....

Computer Control:
Do yourself a favor.  Grab an extension cord and plug the bad set into a regular outlet.  There is nothing more frustrating that trying to test/fix lights while your show is running!

Let's get testing!

1-Unplug everything else:
If you have other strings plugged into the one with the out section, unplug them.  This includes plugs that are stacked.  Technically the LKP should work regardless, but for me it eliminates another reason for false readings.

2-First bulb check:
This step is the most IMPORTANT!  Do NOT skip this step since the readings of the LKP will be out-of-sync with reality if you do.  Always perform the first bulb check!

Press the detector button and test the FIRST bulb in the OUT section.  The LKP instructions will tell you to 'scan' along the set, but I find that putting the tip near the actual bulb gives more accurate readings.  The LKP should start beeping.  If the LKP does NOT BEEP, remove the plug from the socket, flip it 180 degrees and plug it back in.  Re-test the first bulb and the LKP should now start beeping.  If it doesn't, replace the first bulb and repeat this step.  If you still don't get a beep, double check that the fuses are good and that there are no broken wires BEFORE the first socket.

3-Continue 'Scaning'...:
Now you have set where the LKP beeped at the first bulb that is out.  Go to the next bulb and test again.  Continue down the string until the LKP DOESN'T beep.

4-...Until the LKP stops beeping:
The point where the LKP beeps and then doesn't beep is a possible trouble area.  I like to test both of these bulbs a few times.  Go back and forth between the last bulb that beeps and the one that doesn't....  Beep.   Doesn't Beep.  Beep.  Doesn't beep.

5-First check for physical problems:
Once you have determined that there is a definite difference, remove the bulb that doesn't beep.  Examine it when you remove it for corrosion or bulb wires that are not correctly bent around the base.  If you find problems, replace the bulb and correctly bend the wires around the base.  If all looks OK and the set is still out, test the bulb.

6-Next, test the bulb:
Rather than plug the light bulb into the LKP's light tester, I use the 'fuse tester'.  Using the fuse tester instead of the bulb tester saves the LKP's batteries - lighting an LED takes a lot less power than lighting a mini-bulb! 

Spread the 2 wires from the bulb out away from the base.  Keep your fingers off the test button, and 'scratch' the bulb wires over the fuse contacts on the top of the LKP.  Does the LED light or flash?  If not, you have found a bad bulb.  Replace it and 95% of the time the set will light up at this point. 

If the set doesn't light after replacing this bad bulb, check it with the detector.  The LKP should beep.  If it does, you have another bulb which is bad.  Continue scanning down the string until you get to another bulb that doesn't beep and repeat. 

7-The bulb is OK, so check the socket:
If the LED does light, double check the socket.  Are there 2 metal tabs, and are they positioned properly in the socket?  If not, repair the socket (UNPLUG THE SET FIRST!) and replace the bulb. 

8-The socket was OK, so go backward 1 bulb and try again:
If the socket looks OK, replace the bulb and go backward 1 bulb (the one that DOES beep).  Perform the 'bulb checks' and 'socket checks' from above as needed.

9-The set still doesn't light:
Still no luck?  Check for broken wires between the 2 sockets that beep and don't beep.  Check the next couple of bulbs with the detector to see if perhaps you got a false 'no beep reading'.  If at this point the set still won't light, consider replacing the whole thing - you've spent more time trying to get it to work than what it's worth. 

Tips and hints:


The LKP detector function takes practice to use properly. The hardest thing to get used to is the optimal distance away from the set you need to hold the LKP.

The directions say you should scan along the wires with the LKP.  I find that makes for a lot of false readings.  Rather than scan along the wire, I point the tip at the actual bulb.

Be sure to keep your fingers out of the way to reduce false readings.  Pull the bulb and socket up and out of the way, and only hold on to the 'main' wires.

When testing, keep your fingers away from the bulb to prevent false readings

Practice with a working set by removing a bulb from the middle of a section. Take the LKP and see how close, and how far up or down a working bulb you need to be to get the LKP to beep.  Now go to the last bulb in the out section and at the same distance note the difference in the way it reacts.  (Note:  did it beep easier on the last bulb than the first?  If so, remove the plug from the outlet, flip it 180 degrees, plug it back in and repeat).

Now, start at the first bulb and test all the way down.  Pretend that empty socket isn't really there.  Go back and forth between bulbs you know SHOULD be beeping (from the socket up to the missing bulb) and ones that shouldn't (from the missing bulb to the end).  Get used to the orientation and distance of the LKP versus the bulb you are testing.

For a real challenge, cut the wires off of a bulb and stick it back into it's base.  Use this bulb and randomly replace working bulbs with it.  Plug the string back in and find your bad bulb.

Advanced Techniques:


Don't try these until you are absolutely proficient at using the LKP 'the right way'.

Rather than test every bulb, take a page from computer programmers and do a binary search.  To do a binary search, go 1/2 the way up the section of lights that is out and and test. If it beeps, go another 1/2 way UP the bad section toward the end.  Otherwise go 1/2 the way back toward the plug. Keep going back and forth like this, dividing the remaining lights that need to be tested in half until you find the bad bulb. Doing it this way means you only need to test 5 or 6 bulbs to find the bad one.

Example:  Let's assume that bulb #23 is bad.  My first test is at bulb #25, and the LKP doesn't beep.  That means the problem is this bulb or BEFORE.  I go 1/2 way back from bulb #25 to bulb #12 and test again.  This time the LKP beeps.  I now know that the bad bulb is between #12 and #25.  I test bulb #18 since it's 1/2 way between #12 and #25 and the LKP still beeps.  Now I know the bad bulb is between #18 and #25.  I test bulb #22 and the LKP STILL beeps.  Now the bad bulb is between #22 and #25.  I test #24 and the LKP doesn't beep.  Now the bad bulb is either #23 (#22 beeped so it can't be bad), or #24.  #23 is the only one not tested, and sure enough it doesn't beep.  The last bulb to beep is #22, and the fist to not beep is #23.  #23 is the bad bulb.

When doing the binary search, you don't need to be exact in the number of bulbs to skip.  You can 'roughly' go to the center.  For subsequent tests, you can roughly divide the number of remaining bulbs. 

You don't really need to do the plug flip (Step 2, first bulb check) IF you know what you are listening to.  If the first bulb in an out section doesn't beep, but the last one does, simply reverse your thinking.  Scan along the set as normal, but this time replace the first bulb that DOES beep.  If you are doing the binary scan from above, you need to reverse that too.  If the LKP doesn't beep, you need to continue UP the set.  If it does beep, you need to go back toward the plug.


Purchase a Light Keeper Pro from Amazon.