Dome vs Quarter Dome vs Half Dome Mirror: Choosing the Right Geometry
The "dome" family of safety mirrors solves four-way intersections, T-intersections, and single-corner blind spots with different geometries. Picking the right one is geometry, not preference: a quarter dome at a four-way intersection covers one quadrant and leaves three blind. A full dome at a single blind corner wastes 270 degrees of mirror surface. The decision is which intersection type the mirror serves.
What Is the Difference Between a Quarter, Half, and Full Dome Mirror?
A dome mirror is a hemispherical convex safety mirror, typically used indoors, that covers a 90- to 360-degree field of view depending on its geometry. Quarter dome covers one corner (90 degrees), half dome covers a T-intersection (180 degrees), and full dome covers a four-way intersection (360 degrees). Standard sizes run 18 to 36 inches diameter. Cojo installed a 26-inch half dome at a Salem warehouse cross-aisle in March 2026, mounted at 11 feet to mirror center, after a forklift near-miss had been logged at the cross-aisle the previous quarter.
Quarter Dome Mirror: Single-Corner Coverage
Quarter domes give a wide-angle view at one 90-degree corner. The reflective surface is the bottom-rear quadrant of a hemisphere. They are used:
- Indoor warehouse aisle corners where rack rows force a 90-degree turn and one direction of approach is the only concern.
- Indoor parking garage corners where a building wall forces a single-direction blind spot.
- Retail-store interior corners where two aisles meet in a single 90-degree turn.
Quarter domes are not appropriate for outdoor parking-lot use because the open quadrant of the hemisphere collects rain, debris, and snow. They are not appropriate for any intersection where two or more directions of approach matter -- they will leave the other approaches blind.
Standard quarter-dome diameters run 18 to 26 inches. Coverage radius is roughly 4 to 7 times the diameter at typical mounting heights. A 26-inch quarter dome at 10 feet covers a corner reaching about 12 to 18 feet on the approach.
Half Dome Mirror: T-Intersection and Cross-Aisle Coverage
Half domes give a 180-degree view at T-intersections, cross-aisles, and corner-against-wall installations. The reflective surface is half of a hemisphere. They are used:
- Warehouse cross-aisle intersections where forklifts approach from two directions and the third direction is a wall or rack-end (the most common warehouse application).
- Indoor parking garage corners against a wall where the wall blocks one direction and traffic approaches from two.
- Loading dock corner-against-wall installations where the dock wall is the third side.
Standard half-dome diameters run 18 to 30 inches. The 26-inch is the workhorse size for a warehouse cross-aisle with 14- to 16-foot aisle width. Mounting is wall-against; the flat back of the half hemisphere mounts flush to the wall, with the convex curve facing into the intersection.
Full Dome Mirror: 360-Degree Four-Way Intersection Coverage
Full domes give a complete 360-degree view at a four-way intersection where traffic approaches from all directions. The reflective surface is the full hemisphere. They are used:
- Indoor warehouse four-way aisle intersections where forklifts cross at right angles from all four directions.
- Indoor parking garage center-of-intersection mounts where the intersection is centered in an open garage level.
- Retail-store center aisles where shopping carts cross paths at right angles.
Standard full-dome diameters run 24 to 36 inches. Mounting is ceiling-suspended -- the dome hangs from a ceiling-mounted bracket or a chain-suspension kit positioned over the intersection center. Outdoor full-dome installs are uncommon because ceiling-suspension hardware does not exist on most outdoor lot conditions; outdoor four-way coverage typically uses two convex mirrors on opposing pole mounts instead.
Which Geometry Solves Which Problem?
| Intersection type | Best mirror | Standard size | Mount |
|---|---|---|---|
| Single 90-degree corner (one direction of approach) | Quarter dome | 18 in to 26 in | Wall-corner |
| T-intersection (two directions of approach + wall) | Half dome | 18 in to 30 in | Wall-flat |
| Cross-aisle (two directions of approach + wall) | Half dome | 24 in to 30 in | Wall-flat |
| Four-way intersection (four directions of approach, indoor) | Full dome | 24 in to 36 in | Ceiling-suspended |
| Outdoor blind corner (two directions, no ceiling) | Convex (not dome) | 24 in to 36 in | Pole or wall L-bracket |
What About Outdoor Applications?
Dome mirrors are largely indoor products because the open hemisphere geometry traps rain, snow, and debris. Outdoor parking-lot blind corners use standard convex mirrors with a fully sealed back and bracket, not dome geometry. The exception is a covered outdoor space (parking garage, loading-dock canopy) where the cover keeps weather off the dome -- in those cases, half and full dome mirrors are appropriate.
Mounting Hardware Comparison
- Quarter dome: Two-piece wall-corner bracket. The bracket fits into the inside corner where two walls meet. Lag-bolt or anchor mount. Hardware should be galvanized for any moisture-exposed installation.
- Half dome: Flat-back wall mount. Two or four lag-bolt anchor points through the back of the half hemisphere into the wall. Standard aluminum or galvanized steel bracket.
- Full dome: Ceiling chain or rod suspension. Three- or four-point chain rig from ceiling joists or a center-mounted threaded rod. Requires structural attachment to load-bearing ceiling structure -- not drywall ceiling tile.
A common installation error is mounting a half dome on the outside corner of a wall instead of the inside corner. The outside-corner mount leaves the convex curve facing nothing useful and the flat back facing the intersection -- which produces no reflection at all.
What Does Each Geometry Cost?
Industry Baseline Range
| Geometry | Diameter | Mirror cost | Hardware | Install | Total |
|---|---|---|---|---|---|
| Quarter dome | 18 in | $90 to $200 | $40 to $90 | $130 to $280 | $260 to $570+ |
| Quarter dome | 26 in | $160 to $320 | $50 to $110 | $150 to $320 | $360 to $750+ |
| Half dome | 26 in | $200 to $420 | $60 to $130 | $180 to $400 | $440 to $950+ |
| Half dome | 30 in | $260 to $520+ | $70 to $150 | $200 to $480 | $530 to $1,150+ |
| Full dome | 30 in | $320 to $620+ | $130 to $280 | $280 to $620+ | $730 to $1,520+ |
| Full dome | 36 in | $440 to $850+ | $160 to $320 | $320 to $720+ | $920 to $1,890+ |
Current Market Reality
Full-dome ceiling-suspension installs run higher than the baseline because of the structural-attachment labor (joist or beam locate, anchor placement, chain rigging). Half-dome installations on load-bearing wall surfaces are typically the lowest-labor of the dome family. 2026 mirror pricing has tracked 8 to 14 percent above 2025 on polycarbonate and acrylic feedstock; hardware (galvanized steel, stainless) has held flat to slightly elevated.
Real-World Cojo Install: Salem Warehouse Cross-Aisle
On a 64,000-square-foot Salem warehouse in March 2026, Cojo installed a 26-inch half dome at the main cross-aisle intersection. The aisle was 15 feet wide, with 12-foot rack-row spacing on either side. We used a 26-inch acrylic-faced half dome on a flat-back wall mount at 11 feet to mirror center, mounted to the rack-end frame with U-bolt clamps. The previous-quarter near-miss log dropped to zero reported incidents in the 6 months following installation. OSHA aisle-clearance review at the next inspection cited the cross-aisle as previously deficient, now corrected.
OSHA and Code References for Indoor Dome Mirrors
- OSHA 1910.176(a) -- Storage aisle clearance and forklift sight-line requirements; mirrors are referenced as a sight-line aid where direct sight is blocked.
- OSHA 1910.144(a)(1) -- Safety color code framework; mirrors complement the marshaling-paint system.
- OSHA 1910.178(n)(7) -- Powered industrial truck operator visibility requirements; cited where sight-line aids are evaluated.
None of these mandate a dome mirror; they govern the underlying sight-line conditions that dome mirrors complement.
Match the Geometry to the Intersection
A quarter dome at a four-way intersection leaves three quadrants blind. A full dome at a single blind corner wastes most of its reflective surface. The right call is geometry-first: count the directions of approach, identify the wall conditions, and pick the dome that matches. Cojo specifies and installs dome mirrors as part of warehouse and indoor-parking retrofit packages. Contact Cojo for a sight-line assessment.