What is beam orientation?
Where the beam axis points: how far it is turned sideways and tilted up from a reference. The pilot stays where they are, so orientation decides which point on the photometric curve the pilot receives.
Beam orientation is where a fixture’s beam axis points, given as two angles from a reference: how far it is turned sideways, and how far it is tilted up from the horizontal. The beam axis is the line of peak intensity, and it is the zero of every photometric diagram. Orientation therefore says where that zero lands on the airfield.
The pilot is in a fixed direction from the fixture. Turn or tilt the beam by some angle and the pilot is that many degrees off the beam axis, reading a lower point on the curve. Turn the beam by its half-angle (half the 50% beam angle) and a pilot on the old reference line receives half of the peak. The same error costs more on a narrow beam, because half the peak is reached at a smaller angle. A fixture can have its lamp or LED at full output and still look dim from where it should be seen.
The angles of the beam axis, horizontal and vertical, from a reference. The photometric description.
Which way a fixture faces: one way, both ways or all round. The choice of side, not the exact angle.
- Pick the reference. In plan it is the runway or taxiway axis; in the side view it is the horizontal.
- Find the beam axis. It is the line of peak intensity, the zero of the photometric diagram.
- Measure the horizontal angle. Seen from above, how far the beam axis is turned sideways from the reference.
- Measure the vertical angle. Seen from the side, how far the beam axis is tilted up from the horizontal.
- Mark the pilot. The pilot is in a fixed direction from the fixture, so the pilot does not move when the beam does.
- Read the shift. The pilot is now off the beam axis by the orientation angle. Read the intensity at that angle on the curve.
Frequently Asked Questions
Q1What is beam orientation?
Beam orientation is where a fixture's beam axis points, given as two angles from a reference: how far it is turned sideways in plan, and how far it is tilted up from the horizontal. The beam axis is the line of peak intensity, so orientation decides where the zero of the photometric diagram lands on the airfield.
Q2What is the difference between beam orientation and beam direction?
Beam direction says which way a fixture faces: one way, both ways along the runway, or all round. Beam orientation is the exact angles of the beam axis, horizontal and vertical, from a reference line. Direction is the choice of side; orientation is how precisely the beam sits on it.
Q3How does orientation change what a pilot sees?
The pilot is in a fixed direction from the fixture. If the beam axis is turned or tilted by some angle, the pilot is that many degrees off the axis and reads a lower point on the photometric curve. Turn the beam by half its 50% beam angle (the half-angle) and a pilot on the old reference line receives half of the peak intensity.
Q4Why does a small error matter more for a narrow beam?
A narrow beam reaches half intensity at a small angle off the axis. The same orientation error is therefore a larger share of the half-spread, and moves the pilot further down the curve, than it would for a wide beam.
Q5Can a working lamp look dim because of its orientation?
Yes. The lamp or LED can be producing its full output while the beam points slightly away from the observer. The light then looks dim or is not seen from where it should be, so a dim light is not proof of a weak source. Check the orientation as well as the lamp.
Q6Is beam orientation the same as fixture alignment?
They are closely linked. Beam orientation is the photometric description: the angles the beam axis has from the reference. Fixture alignment is the installation and maintenance work of setting those angles and checking them. The required angles come from the applicable standard and the manufacturer's data.
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