Wednesday, January 4, 2017

CIE88 2004, Calculation of Tunnel Lighting Transition Zone Length

This article is a bit of extra help for this one (on CIE88 2004).




We know that we need to arrive at an internal tunnel luminance Lin, and we know we start at the formula for calculating the curve is the one given above, Ltr. 

Time and distance are related by the fixed velocity, v, of the tunnel project. If we get the time taken to go through the transition zone we can easily get the length of the transition zone.

Re-arranging the original equation...




So you can calculate d, the length of the transition zone, from these three things:
  • the project velocity
  • the threshold luminance
  • the internal luminance.
(Thanks to Bui Duc Han for correcting an error in a previous version of the steps above.)


3 comments:

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  2. Hi Owen,
    very nice blog explaining clearly the problems related to photometric calculations!
    I found one formal issue however: in the formula for Lin one can find the (1.9 + t) term. t looks for me like distance rather than time (although for a constant velocity they are effectively equivalent), particulary, when placed in the figure of a tunnel profile. You could easily avoid this ambiguity by putting (1.9 + v*t) for a constant v.

    One more question: I guess that the function aproximating Ltr, i.e., Ltr = Lth(1.9+t)^-1.4 is an arbitrary one (with border conditions fixed only), am I right?

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    1. The original CIE88 2004 standard uses that notation, t not d, and has 4 scales under the graph which shows the distance travelled at 60 80 100 and 120 km hour. I stuck to their way of doing it!

      Standards! Arbitraryness! What are you suggesting? ;) I think it was a reasonable er, approximation to what they were trying to achieve...

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