Exterior is less forgiving than interior, because there are no walls or ceiling to bounce light around and fill in the gaps. What you aim is what you get. That makes distribution type and pole spacing more important than fixture wattage, and it is why two lots with the same average foot candles can look completely different.
Distribution types
The Roman numeral on a spec sheet describes the shape of the light pattern on the ground. Getting it right is most of the job.
| Type | Pattern | Use it for |
|---|---|---|
| Type II | Long and narrow, thrown forward | Wide walkways, bike paths, narrow roadways, poles close to the edge of what they light |
| Type III | Wider forward throw, the general purpose pattern | The default for parking lots. Poles at the perimeter or in islands, lighting forward and to the sides. |
| Type IV | Semicircular forward throw, almost nothing behind | Poles right against a building wall or property line, where light behind the pole is wasted or unwanted |
| Type V | Symmetrical circle or square in every direction | Poles in the middle of a large open lot, roundabouts, open areas with the pole at the centre |
Choosing in practice
- Pole in the middle of the lot. Type V. The light needs to go every direction.
- Pole on the perimeter facing in. Type III, or Type IV if there is a property line right behind it.
- Pole against the building. Type IV. Anything thrown backward hits the wall.
- Row of poles down one side of a long lot. Type III, sometimes Type II if the lot is narrow.
- Two rows of poles facing each other. Type III on both, and let the patterns overlap in the middle.
Mixing distributions on one lot is normal. Perimeter poles on Type IV and island poles on Type V is a very common and correct layout. A single distribution across a whole site is usually a sign nobody looked at the pole positions.
Pole spacing
| Pole height | Typical spacing | Typical wattage |
|---|---|---|
| 15 ft | 45 to 60 ft | 40 to 80W |
| 20 ft | 60 to 80 ft | 80 to 150W |
| 25 ft | 75 to 100 ft | 150 to 240W |
| 30 ft | 90 to 120 ft | 240 to 320W |
Higher poles cover more ground per fixture, so a 30 foot layout uses fewer poles than a 20 foot layout on the same lot. The tradeoff is cost per pole, wind load on the base, and the fact that taller poles put more light where you may not want it. Many municipalities cap pole height, so check before you design around 30 feet.
Uniformity is what people actually see
A lot at 1.5 foot candles average sounds fine. If that is 6 foot candles under each pole and 0.2 in between, the lot is unusable at night, because the eye adapts to the bright pool and then cannot see into the dark one. The average was correct and the design failed.
Maximum to minimum: 15:1 or better
| Lot type | Average target |
|---|---|
| Basic, low activity | 0.5 to 1 fc |
| Standard commercial | 1 to 2 fc |
| Retail, hospitality, higher security | 2 to 3 fc |
| Covered entry, drop off | 5 fc |
| Car dealership display | 10 to 20 fc |
More targets by space type are in foot candle requirements by space type.
Dark sky and light trespass
This is now the most common reason a fixture order gets rejected on inspection.
- Full cutoff is increasingly required. No output above horizontal. Look for a BUG rating with U0, meaning zero uplight.
- CCT caps are spreading. A number of jurisdictions now cap exterior lighting at 3000K. Selectable CCT fixtures make this a switch setting rather than a reorder.
- House side shields block light at a property line without changing the fixture. Cheaper than redesigning a layout.
- Curfew dimming is required in some ordinances. A fixture that can dim to 50 percent after a set hour satisfies it and saves energy anyway.
Reading a BUG rating
BUG stands for Backlight, Uplight and Glare, each scored zero to five, lower being more controlled. Backlight is what goes behind the pole, uplight is what goes into the sky, glare is high angle output toward the eye. An ordinance will often specify a maximum for each. It is on the spec sheet.
Mounting
| Mount | Fits |
|---|---|
| Slip fitter | Round tenon on top of a pole, usually 2 to 3 inch. Most common on retrofits. |
| Square pole arm | Bolts to the side of a square pole. The standard on new construction. |
| Round pole arm | Same, with a curved adapter plate for a round pole |
| Trunnion or yoke | Aimable, for walls, poles and flat surfaces where you need to point it |
| Direct wall mount | Building mounted, no pole. Consider a wall pack instead. |
Measure the existing tenon before you order a retrofit. Pole tops are not standardised, and a slip fitter that does not fit means either an adapter or a return. Photograph the pole top and the bolt pattern at the base while you are on site.
Retrofitting an existing lot
- Keep the poles if they are sound. The concrete base and the pole are most of the cost. Check the base for cracking and the anchor bolts for corrosion first.
- Do not match wattage, match delivered light. A 400 watt metal halide shoebox is usually a 120 to 150 watt LED. See metal halide equivalents.
- Check the circuit. LED draws far less, so existing conductors are almost always fine, but confirm the voltage. 480V is common on older lots and not every fixture accepts it.
- Add photocells if the lot runs on a time clock. Time clocks drift and nobody resets them after a power cut, so the lot ends up burning during daylight.
- Take before readings. A meter walk before demo settles any later argument about whether the new lighting is an improvement.
24 area lights, Type III, IV and V
Slip fitter, pole arm and trunnion mounts, photocell and sensor options, with the distribution type and BUG rating on every product page.
Shop area lights