# What constitutes "the lights delineating the runway"?

ICAO defines RVR as "The range over which the pilot of an aircraft on the centerline of a runway can see the runway surface markings or the lights delineating the runway or identifying its centerline."

What are "the lights delineating the runway" here? Do they just point to runway edge lights? Or do they include approach lighting systems as well?

• @Ralph J You're right. It's corrected now. Thanks Jul 18, 2017 at 19:27

I guess the keyword here is delineate. Websters dictionary, definition 1B says:

to mark the outline of, Example: lights delineating the narrow streets

So I would take that to mean the runway edge lights, NOT the approach lighting systems.

Presumably it's your runway lighting (edge lights, such as HIRL, MIRL, etc, plus runway end identifier lights - REIL), centerline lights, and touchdown zone lights only, because being able to see the nearest approach light miles away isn't helpful if, by the time I'm at 200' half a mile from the runway (and past that outer-most approach light), I'm inside a dense fog bank with an RVR of 600 feet.

That said, it's a much more common case where the RVR at the runway (where it's measured) is about the same as the in-flight visibility farther out on final, so with an RVR of 4000' you can expect to see the threshold at typical Cat I ILS minimums of 200' AGL (okay, ATDZE for the pedantic & precise), but at 1800 RVR at the same point, you expect to see approach lights but little else.

• What if the RVR on the chart is 2400ft. I've always thought a way to determine the RVR 2400 ft on an ILS approach is to look for the white roll bar, which is 1000ft away from the runway threshold. So is this method technically wrong because it uses part of the approach lighting system to determine RVR? Jul 18, 2017 at 19:32
• @lemonincider If you DO see the required references (runway, markings, lights, etc) at minimums, then you DO have the necessary flight visibility & may continue the approach; if you don't, then you don't and you can't (well, shouldn't). There is no further need to estimate your visibility, and I've never heard of any training or techniques for doing so. Certainly would NOT discontinue an otherwise landable approach because "this only looks like 2000 RVR, not 2400."
– Ralph J
Jul 18, 2017 at 23:00

It definitely does not include approach lights. One way to measure RVR is to ask the firecrew to drive to the threshold of the runway, climb onto the firetruck and then count how many centerline lights they can see. Centerline lights are spaced by a fixed distance (usually 30 or 60 metres), and so converting the number of lights visible to an RVR value is trivial.