Ceiling Height Sets the Fixture, Layout Sets the Count
Two separate calculations decide a high bay job and people usually only do the first. Picking the right fixture for the mounting height is straightforward. Working out how many of them and where they go is what determines whether the floor is evenly lit or striped with bright pools and dark gaps.
Start With Mounting Height
Light falls off sharply with distance, so the same fixture that over-lights a 15 foot ceiling leaves a 35 foot ceiling dim. Lower mounting heights, in the range where a shop or a service bay sits, are served well by fixtures at the lower end of the wattage range in this collection. Standard warehouse ceilings around 20 to 25 feet move into the mid range. Tall distribution and manufacturing bays above 30 feet need the high end, or they need more fixtures at mid output, which is sometimes the better answer for uniformity.
Compare lumens rather than watts when narrowing choices. Efficacy varies between product lines, and two fixtures at identical wattage can differ meaningfully in delivered light. Wattage tells you the operating cost. Lumens tell you what lands on the floor.
UFO, Linear, or Hazardous-Rated
The shape follows what is underneath the fixture, not personal preference.
- UFO: a compact round disc throwing a circular pattern, the default for open floor area, assembly space, and wide bays with no racking
- Linear: a long fixture whose beam matches the shape of an aisle, which is what makes it the right answer over racking, conveyor lines, and narrow work areas
- Hazardous-location: sealed and certified for a specific Class and Division, required where flammable vapors or combustible dust are present
The aisle case is worth emphasizing because it is the most commonly gotten wrong. A round fixture over a rack aisle wastes a large share of its output on the tops of the racks and leaves the vertical faces, where people actually need to read labels, poorly lit. A linear fixture aligned with the aisle puts the light where the work is.
Beam Angle and Optics
Most UFO high bays are offered with a choice of beam angle, and it interacts directly with mounting height. A narrow beam concentrates output downward and is the right choice for tall ceilings, where a wide beam would spread the light too thin before it reaches the floor. A wide beam covers more area from a lower mount and gives softer overlap between fixtures. Getting this backwards is a common cause of a lighting layout that measures correctly on paper and looks blotchy in person. Some fixtures accept a separate reflector or lens accessory to change the distribution after the fact.
Spacing and Layout
Uniformity comes from spacing relative to mounting height rather than from any fixed dimension. As a working rule, spacing between fixtures is set as a ratio of the height they hang at, and the manufacturer publishes a spacing criterion for each product that states the maximum ratio before uniformity degrades. Higher mount, wider spacing. Narrow beam, tighter spacing. Perimeter rows go closer to the walls than the interior spacing would suggest, because fixtures at the edge only contribute light in one direction.
On any job past a handful of fixtures, ask for a photometric layout before ordering. It costs nothing from most manufacturers, it converts guesswork into a fixture count, and it is the difference between a relamp that hits the target footcandle level and one that needs fixtures added after the fact.
Replacing Metal Halide, and the Restrike Advantage
Most high bay work is replacing older metal halide or high-pressure sodium fixtures, and the energy saving gets all the attention while a second benefit gets overlooked. A metal halide lamp that loses power needs to cool before it will restrike, which means a brief utility dip leaves a warehouse dark for several minutes. LED comes back instantly. In a facility where a momentary outage currently stops work while the ceiling warms back up, that alone can justify the project independent of the energy math.
The other quiet advantage is lumen maintenance. Metal halide loses a substantial share of its output over its life, so a fixture that met the specification when new falls below it long before it fails. LED depreciates far more slowly, which means the design level holds.
Selectable Wattage, Selectable Color, and Dimming
Many current high bays carry switches on the fixture that set wattage, color temperature, or both before installation. On a large order this collapses several part numbers into one and lets the final level be decided once the fixtures are up and the space can be measured. Set every fixture in a bay to the same position, and record what that position was, because a fixture replaced years later on a different setting stands out immediately.
Dimmable drivers open up controls that matter more in a warehouse than in most buildings. Aisles that are used intermittently can sit at a low level and come to full output on occupancy, which cuts energy substantially without anyone noticing the lighting. Lumera's occupancy and motion sensors collection covers the controls used for that.
Ambient Temperature and Environment
Warehouses are frequently unconditioned, and LED drivers have a rated ambient operating range that a hot roof space in summer can exceed. A fixture running above its rated ambient loses life quickly and may drop output to protect itself. Check the rating against realistic summer conditions at ceiling level rather than at floor level, since the difference between the two in a tall building is considerable.
Wet, dusty, and washdown environments need a sealed fixture rather than a standard high bay, and Lumera's vapor tight fixtures collection covers those.
Where flammable vapors or combustible dust are present, the fixture has to be certified for the specific area classification, which the hazardous location lighting collection covers.
Mounting and Installation
UFO fixtures typically hang from a hook and chain or a threaded pendant, which makes them fast to install from an existing outlet. Linear fixtures suspend on aircraft cable or surface mount directly to a structure. Either way, confirm the structure can carry the fixture weight plus any seismic or dynamic requirement the local code imposes, and confirm the hanging point is rated rather than convenient. These are line-voltage fixtures installed at height on commercial circuits, often at 277V or 480V, so a licensed electrician should handle the connection and the circuit verification.
Other Fixtures for the Same Buildings
High bays cover the open volume, and the rest of a facility usually needs something different. For aisles, racking, and lower-ceiling areas where a continuous line of light works better, the strip lights collection covers those fixtures.
For the attached office, breakroom, and administrative areas with standard suspended ceilings, the LED panel lights collection covers that side of the building.
High Bay Lighting Questions, Answered
How do I know what wattage high bay to use?
Start from mounting height, since light falls off sharply with distance. Lower shop and service bay ceilings suit the lower end of the wattage range, standard warehouse ceilings the middle, and tall industrial bays the high end. Then compare lumens rather than watts, because efficacy differs between product lines and two fixtures at the same wattage can deliver different light.
Should I use UFO or linear high bays?
Match the shape to what is below. UFO fixtures throw a circular pattern that suits open floor and wide bays. Linear fixtures match the shape of an aisle, which makes them the right choice over racking and conveyor lines, where a round fixture wastes output on the tops of racks and under-lights the vertical faces people read.
How far apart should high bay fixtures be spaced?
Spacing is set as a ratio of mounting height, not as a fixed distance, and each product publishes a spacing criterion giving the maximum ratio before uniformity suffers. Higher mounting allows wider spacing, and narrower beams need tighter spacing. Perimeter rows sit closer to the walls than interior spacing suggests. On anything beyond a few fixtures, request a photometric layout.
Does beam angle matter?
Considerably, and it interacts with mounting height. A narrow beam concentrates output downward and suits tall ceilings where a wide beam would thin out before reaching the floor. A wide beam covers more area from a lower mount with softer overlap. Getting it backwards produces a layout that calculates correctly and looks patchy in the space.
Is it worth replacing metal halide beyond the energy saving?
Often yes, for two reasons people overlook. Metal halide cannot restrike until it cools, so a momentary utility dip leaves the building dark for minutes while LED returns instantly. And metal halide loses a large share of its output over its life, so a design that met the target when new falls below it long before the lamps fail.
Will these fixtures handle an unconditioned warehouse in summer?
Check the rated ambient operating temperature against conditions at ceiling level, not at the floor, because the difference in a tall unconditioned building is substantial. A driver running above its rated ambient loses life quickly and may reduce output to protect itself.
