# AE PE practice problem #108?!?

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### #1 bkeefer01

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Posted 07 March 2012 - 05:30 AM

Please don't read this if you plan to go through the Principles and Practice of Engineering book all at once like a practice exam.

But I'm sorry, I don't understand and reservedly disagree with the answer found in the back of this book for problem #108:

108. The term for the ratio of the Luminance leaving a surface area to the illuminance arriving on the surface is:

a. Exitance
b. Transmittance Factor
c. Luminance Factor
d. Luminous Flux

Option d deals with the amount of emanating from a source, so that is out.

My first thought is that the answer was exitance, which is a measure of light leaving a surface. But then I realized that it wasn't a ratio of leaving to arriving luminance. Still quite unsure, I deduced it might have to be either transmittance or luminance factor. The problem is that the word "leaving" is quite ambiguous and even though I have checked the answer in the back of the book to be c, I can't explain why.

Does any have sound logic on this issue that will help me gain confidence to move past this problem?

### #2 linuxpenguin

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Posted 16 March 2012 - 07:16 PM

Sounds like a poorly worded question honestly. "C" is a ratio under ideal circumstances, and that's not specified in the quesiton; whereas "A" is more defined as the ability to emit radiation. "C" would be the "most correct" answer, albeit the question is flawed.

Simply my 2 cents, nothing more.

### #3 simpatique

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Posted 31 March 2012 - 08:29 PM

Flux is defined as flow per unit area , Exitance is M Lumens per square meters . Since the question is about ratio ( unitless ) A and D are impossible . Between transmitance , transmitance (rate) sounds like the best answer However ZEN MASTER once said : when the light leave a room the room gets dark and when the light returns to the room luminates again ! Rate of light / no light. Luminous (lumiere) rate light to no light is the correct answer.
Bullshit ? well , maybe

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