Size outdoor lamp posts like a lighting designer: mounting height from coverage, post spacing for uniform light, lumens and wattage, foundation depth and concrete, solar vs wired planning, zone placement, and a full cost estimate. All calculations run in your browser — nothing is uploaded.
Post height from coverage
Spacing between posts
Lumens & wattage picker
Foundation sizing
Solar vs wired planner
Placement planner
Enter a run length per zone. Presets come from industry guidance (e.g. 7 ft post-mounted lights per outdoor-lighting guides, 50% pool overlap for uniformity).
Cost estimator
Prices are US averages (2025–2026): edit any number to match your local store. Concrete bags $7.50, wire $0.45/ft, trenching $8/ft, labor $65/hr, panels $1.10/W, batteries $0.55/Wh.
How the math works
Light pool diameter from mounting height H and beam half-angle θ: D = 2·H·tan θ; inverted for height: H = D / (2·tan θ). The area-lighting rule of thumb (electrical design guides) is H ≈ area width / 2. Uniform spacing overlaps the pools: S = D·(1 − overlap) with 50% overlap as the default; the parking-lot industry guide (20–25 ft poles spaced 30–40 ft) is used as a sanity check. Lumens come from the lumen method Φ = E·A / (CU·LLF) with CU 0.45 and LLF 0.85 for outdoor posts, and watts from LED efficacy. Foundations use the ⅓-burial rule (min 2 ft, +25% in high wind) with a hole 3× the post diameter; concrete volume is the annulus between hole and post. Solar sizing is nightly energy ÷ (depth of discharge × driver efficiency) for the battery and ×1.2 ÷ peak sun hours for the panel. Mounting-height-by-wattage bands follow the City Electric Supply lamp chart (HID guideline).
How tall should my lamp post be for the area I want to light?
Mounting height comes from beam geometry: height = pool diameter ÷ (2 × tan(beam half-angle)). A 24 ft light pool with a 120° beam needs the fixture at about 6.9 ft; a 40 ft pool with a 90° beam needs exactly 20 ft. As a rule of thumb, mounting height ≈ half the width of the area being lit. Lamp mounting charts put ~100 W fixtures at 15–20 ft and ~150 W fixtures at 20–25 ft.
How far apart should outdoor lamp posts be spaced?
Space posts so the ground light pools overlap about 50%: spacing = pool diameter × (1 − overlap). A 7 ft post with a 120° beam throws a 24.2 ft pool, so spacing ≈ 12.1 ft — a 100 ft path needs 10 posts. This matches the parking-lot industry guide (20–25 ft poles spaced 30–40 ft apart): the same formula gives 34.6 ft spacing for 20 ft poles.
How many lumens do I need for a driveway or pathway?
Use the lumen method: lumens = lux × area ÷ (CU × LLF). A 20 × 12 ft driveway (240 sq ft) lit to 15 lux for security needs about 874 lumens — roughly a 7.3 W LED at 120 lumens per watt. Typical outdoor targets: security 15 lux, pathway 10 lux, ambience 5 lux, garden accent 2 lux.
How deep should a lamp post foundation be, and how much concrete?
Bury one-third of the above-ground height: a 7 ft post needs 28 in of burial, a 14 ft post 56 in (4 ft 8 in); in high-wind areas go 25% deeper. Dig the hole 3× the post diameter — a 3.5 in post needs a 10.5 in hole, taking about 3 bags of 80-lb concrete; a 14 ft post on a 4 in pole takes 6 bags. For reference, a 14 ft, 4 in post sees about 96.8 lb of wind force at 90 mph.
What size solar panel and battery does a solar lamp post need?
Size from nightly energy. A 15 W fixture running 10 hours uses 150 Wh per night. With LiFePO4 (90% depth of discharge) you need about a 185 Wh battery, and at 4 peak sun hours a 55.6 W solar panel. Lead-acid needs roughly double the battery because only 50% is usable.
How far can 12 V low-voltage landscape wire run?
Voltage drop limits the run: a 60 W load on 12 AWG cable at 12 V can run about 453 ft one-way before hitting 5% drop. Size the transformer at 125% of the load — 75 VA for 60 W of fixtures. Keep runs balanced on both transformer taps when possible.
How many lights do I need for a pathway, driveway, or garden?
Divide the run length by the recommended spacing and add one. The planner presets: a 100 ft pathway with 7 ft posts needs 10 posts at 12.1 ft spacing; a 60 ft driveway with 9 ft posts needs 5 posts at 18.7 ft spacing; garden accent posts sit lower (4 ft) with a narrower beam.
Is solar or wired cheaper for lamp posts?
Per post the costs are surprisingly close in this example: 6 solar posts cost about $1,624 ($270.67 per post, panels and batteries included), while 10 wired posts cost about $2,677.50 ($267.75 per post, including trenching, wire, and transformer). Solar wins when trenching is expensive or impossible; wired wins for bright, all-night output. Prices are US averages — adjust the unit prices in the calculator.
Do I need an electrician to install a lamp post?
Low-voltage 12 V systems are generally DIY-friendly and need no conduit in most jurisdictions. Line-voltage (120/230 V) posts must meet local electrical code and usually require a licensed electrician. Always check local code before digging — in the US call 811 to mark utilities first.
Estimates only — not a substitute for a licensed electrician or structural engineer. Always check local electrical and building codes, and call 811 (US) before digging. Mounting-height bands are HID-lamp guidelines; LED equivalents use ~90 lm/W HID efficacy for comparison.
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