ICAO recommends that aircraft stands are illuminated to an average horizontal illuminance of at least 20 lux. However, simply stating “20 lux” does not tell the whole story.
Illuminance must be measured on a defined plane. On an aircraft stand, the two main measurements are horizontal illuminance and vertical illuminance.
Both are measured in lux, but they assess different parts of the working environment and are measured in different ways.
What is horizontal illuminance?
Horizontal illuminance measures the light falling onto a horizontal surface.
On an aircraft stand, this normally means the apron surface. It helps determine how clearly people can see:
- Apron markings
- Equipment and cables on the ground
- Vehicle routes
- Surface hazards
- The area around the aircraft
To measure horizontal illuminance, a lux meter is positioned horizontally with the sensor facing upwards.
The commonly referenced ICAO recommendation for aircraft stands is:
- 20 lux average horizontal illuminance
- An average-to-minimum uniformity ratio of no more than 4:1
This means that achieving a 20 lux average is not enough on its own. The lighting must also be reasonably even across the stand.
For more information, read our guide to what apron floodlighting uniformity means.
What is vertical illuminance?
Vertical illuminance measures the light falling onto an upright surface.
On an aircraft stand, it helps determine how clearly people can see:
- Ground handling personnel
- Vehicles and equipment
- The aircraft fuselage
- Passenger steps
- Baggage containers
- Fuel and catering vehicles
Vertical illuminance is commonly assessed at a height of 2 metres above the apron surface.
The lux meter is held vertically, but the direction it faces matters. A reading taken facing a floodlight may be much higher than one taken facing away from it.
The lighting design or survey should therefore state which directions are being assessed, such as towards the aircraft, terminal or main working area.
What is the difference?
The simplest explanation is:
Horizontal illuminance helps people see what is on the ground. Vertical illuminance helps people see what is in front of them.
| Horizontal illuminance | Vertical illuminance |
|---|---|
| Measured on a horizontal plane | Measured on a vertical plane |
| Normally assessed at apron level | Commonly assessed 2 metres above the apron |
| Shows how well the ground is lit | Shows how well people, vehicles and aircraft surfaces are lit |
| Sensor faces upwards | Sensor faces a defined direction |
Can an aircraft stand meet the horizontal requirement but still have poor vertical lighting?
Yes.
A lighting system may deliver enough light onto the apron surface while leaving people, vehicles or the side of the aircraft in shadow.
This can happen when:
- Floodlights are aimed too steeply downwards
- Most light is concentrated close to the mast
- The optics do not project light effectively across the stand
- Lighting comes mainly from one direction
- Aircraft or equipment create shadows
This is why horizontal and vertical illuminance should be calculated separately.
Why average lux is not enough
An average lux value can hide dark areas.
For example, one part of the stand may be very bright while another is poorly lit. The overall average may still appear acceptable.
A complete aircraft stand lighting assessment should therefore consider:
- Average horizontal illuminance
- Minimum horizontal illuminance
- Uniformity
- Vertical illuminance
- Glare
- Shadows
- Luminaire aiming
Simply increasing the wattage or lumen output will not always improve the result. Mast position, optical distribution and aiming are often just as important.
You can learn more in our guide to airport apron floodlighting standards.
How should illuminance be measured?
Before carrying out an aircraft stand lighting survey, the airport should define:
- The area being assessed
- The measurement grid
- The required horizontal and vertical levels
- The height of the vertical measurements
- The directions in which vertical readings will be taken
- Whether the target is an average or minimum value
Readings should be taken across the full operational area, not only beneath the floodlight masts or in the brightest locations.
The meter orientation, measurement height and location should also be recorded so that the results can be compared accurately with the lighting design.
Frequently asked questions
What horizontal illuminance is recommended for an aircraft stand?
ICAO guidance commonly referenced for aircraft stands recommends an average horizontal illuminance of 20 lux, with an average-to-minimum uniformity ratio of no more than 4:1.
At what height is vertical illuminance measured?
Vertical illuminance on an aircraft stand is commonly assessed at 2 metres above the apron surface.
Does every point on the stand need to reach 20 lux?
No. The 20 lux figure refers to the average horizontal illuminance. The uniformity requirement controls how low the darkest point can be.
Why does the direction of a vertical measurement matter?
Vertical illuminance is directional. The result changes depending on which way the sensor faces, so the measurement direction must be defined and recorded.
Can horizontal illuminance be good while vertical illuminance is poor?
Yes. A stand may be well lit at ground level while people, vehicles and aircraft surfaces remain poorly illuminated.
Summary
Saying that an aircraft stand requires 20 lux does not provide enough information on its own.
Airport operators also need to know:
- Whether the value refers to horizontal or vertical illuminance
- Where it is measured
- At what height it is measured
- Which direction the vertical plane faces
- Whether the figure is an average or minimum
- What uniformity must be achieved
Horizontal and vertical illuminance measure different aspects of the lighting environment. Both should be assessed to ensure the aircraft stand is illuminated clearly and consistently for ground operations.