Tunnel entrance light: the threshold, not the bore
The entrance zone is where the eye is still adapted to daylight and the road surface has to be lifted to meet it. It is the most heavily loaded part of a tunnel and the part that decides the scheme's control.
Specification
What the sheet states for this build, and what is confirmed per project.
| Topic | What the sheet states |
|---|---|
| Zone | Threshold, with the length derived from the approach |
| Level | From the design luminance and the calculation |
| Optic | Asymmetric, aimed down the bore |
| Control | Luminance sensor and a dimming curve |
| Housing | Corrosion class and wash down, per project standard |
| Access | Partial or full closure, agreed with the operator |
| Sealing | Gasket type, and how it is replaced |
| Certification | File per model and market |
| Data sheet | Current revision, naming the delivered model |
The threshold level is not a constant. It follows the luminance outside, so the installation is specified with a control curve, not with a fixed output.
The luminance step
Approaching a tunnel, the eye adapts to the bright surround. The bore then appears as a dark hole, and the lighting has to lift the road surface inside the portal to a level the adapted eye can use at the approach speed. That level is a multiple of the interior level, and the multiple falls as the driver goes deeper.
The result is a stepped design. The first run is loaded, the next is less, and the interior holds the base level. A scheme that carries one level through the portal either over lights the bore or under lights the entrance.
- The approach luminance the design is based on, and how it is measured.
- The length of each zone, from the design speed.
- The control curve, and the sensor that drives it.
A portal facing east is not a portal facing north
Portal orientation changes the luminance in front of it through the day. An east facing portal has a bright morning and a milder afternoon; a north facing one rarely sees direct sun on the approach. Two identical bores can therefore carry different threshold designs.
This is why a tunnel fixture cannot be selected from a catalogue page. The design starts with a luminance reading and a geometry, and the fixture is chosen to deliver what the calculation needs down the bore.
- Orientation and the sun path across the approach.
- Whether the approach is in open sky or under a canopy.
- The road surface, which changes the reflected luminance.
Dust, exhaust and access
The threshold zone is where the dirt arrives first, carried in on the vehicles and settling on the first luminaires. The maintenance factor assumes a cleaning interval, and the interval is only realistic if the access is realistic.
The luminaire has to be reachable in the closure regime the operator will actually grant: a rolling lane, a night stop or a full closure. Ask which, and design the access for that, not for the ideal.
- The closure regime the operator will grant.
- The cleaning interval behind the maintenance factor.
- A gasket and lens that can be replaced in that window.
Before the order
- Zone lengths from the design speed, with the calculation per zone.
- Control curve and sensor, agreed with the control contractor.
- Closure regime, which decides how the fixture is serviced.
- Build
- Tunnel entrance light
- Line
- Tunnel lights
- Ask for
- Specification sheet, photometric file, aiming drawing
Send the space, get the sheet.
Build, specification sheet and the option list for each line item, in one reply.