Solar Post Cap Sizing FAQ: Base Fit and Placement

This solar post cap light sizing and placement FAQ is base compatibility plus troubleshooting: tape the actual post, pick the 4x4, 5x5, or 6x6 adapter that sits tight and level, then place the IP44 cap where the panel sees sky. A 15-lumen warm white head with a 1000MAH Ni-MH cell will not charge on a cocked or shaded top. Most "wrong size" complaints are nominal lumber, vinyl sleeves, or a cap still sitting on an old decorative lid.

Sizing is the tape; placement is the sky

Compatibility means the base matches actual width and depth, not the stamp. Placement means the 6-pack goes on posts that can fill the cell. Troubleshooting starts by naming which one failed. A perfect fit in eave shade is still a dark night. A perfect sunny 6x6 with a rocking 4x4 adapter is still a dark night.

Measure every unique deck and fence top. Dry-fit. Choose the tightest base that does not crack vinyl. Press until the gasket is even. Automatic sensors should face true dusk after you lock placement. Eight SMD LEDs at 15 lumens are the output you are placing — markers, not bay floods — so spacing follows post rhythm, not a fantasy grid.

Charts and material notes: size and adapter guide, base sizing fit guide, post sizing FAQ, vinyl compatibility FAQ.

Troubleshooting compatibility by what you see

Rocks: too-large base. Will not drop on: too-small base or old cap in the way. Sits high on vinyl: flared sleeve or wrong adapter. Placement looks even by day but dark by night: shade, dirt, or sensor glare — not sizing. Mixed old and new sections: several actual sizes in one run; compatibility is per post.

Do not foam-wrap wood in a way that holds water. Do not shave vinyl. Optional tab screw on the base if wind lifts a correctly sized cap. Never through the battery tray.

| FAQ symptom | Sizing or placement? | Troubleshooting | | --- | --- | --- | | Rattles on wood 4x4 | Sizing / compatibility | Tighter adapter; actual is smaller | | Tight on one 5x5, loose on the next | Compatibility | Measure each top | | Level but dim | Placement | Sky, wash, sensor, then 1000MAH cell | | High on vinyl | Sizing | True OD; do not force | | Even gaps, dark bays | Placement | 15 lumens mark posts, not bays | | Blows off | Sizing plus wind | Correct base; tab screw |

Placement rules that sizing cannot skip

Put gates, corners, and stairs first. Skip deep shade. Keep warm white so a "placement problem" is not a cool-white leftover. Charge a clear day before you call compatibility a failure. DIY is $0; an electrician at $50–$100 per hour will not tape a post for you.

Sizing and placement checklist

[ ] Tape actual width and depth of every unique post.
[ ] Dry-fit 4x4, 5x5, and 6x6 bases; keep the tightest that seats.
[ ] Confirm the panel is level — compatibility includes the sky angle.
[ ] Place the 6-pack on sunlit gates, corners, and deck newels first.
[ ] Aim automatic sensors away from house lamps.
[ ] Wash panels after seating; film is fake shade.
[ ] Press down after rain; wood moves.
[ ] Judge 15 lumens at the post, not as bay fill.

Frequently asked questions

Will one base size fit my whole fence?

Only if every actual top matches. This sizing FAQ assumes mixed compatibility until you measure.

Is a 6x6 deck post the same as a 6x6 fence post?

Same label, maybe different actual. Troubleshooting starts with the tape.

Can placement fix a loose base?

No. Placement is sky. Sizing is the adapter. Do both.

Why does a cap fit in the shop photo and not on my vinyl?

Photos show a post. Your sleeve has a different outside dimension. Compatibility is local.

Do I need spacers for 15-lumen brightness?

No. Brightness is the spec. Spacing is whether you can see the next post, not a lumen trick.

What to do next

Tape the worst-fitting post and the darkest post. Fix compatibility on the first with a tighter base; fix placement on the second with sky. This sizing and placement FAQ ends at those two measurements.

Solar Post Cap Light Sizing & Placement FAQ: Base Compatibility and Troubleshooting