(42S) Room Cavity Ratio, Luminous Intensity and Illuminance

[Eddie W. Shore]

Blog entry: http://edspi31415.blogspot.com/2019/05/h...ratio.html

Room Cavity Ratio

The room cavity ratio is used to assist in calculating lighting efficiency in determining where to place ceiling lights in an office room. The formula is:

RCR = INT( ( 5 * H * ( L + W ) ) / ( L * W ) )

where:
L = length of the room
H = height difference between floor cavity and ceiling cavity
W = width of the room

HP 42S/DM42/Free42: Solver RCR

Code:

LBL "RCR"
MVAR "H"
MVAR "L"
MVAR "W"
MVAR "RCR"
5
RCL * "H"
RCL "L"
RCL + "W"
*
RCL "L"
RCL * "W"
÷
IP
RCL - "RCR"
END

Examples:

Example 1:
Input: H = 5.5, L = 16.8, W = 13.7. Result: RCR = 3

Example 2:
Input: H = 5.5, L = 16.8, RCR = 4. Result: H = 7.1650

Sources:

Dilouie, Craig. "Lighting Design: Example of Role Surfaces Play in Lighting Efficiency" LightNOW https://www.lightnowblog.com/2010/06/exa...fficiency/ June 16, 2010. Retrieved March 31, 2019

"Room Cavity Ratio, RCR" Illuminating Engineering Society. https://www.ies.org/definitions/room-cavity-ratio-rcr/ July 5, 2018. Retrieved April 28, 2019

Luminous Intensity and Illuminance

The follow equation relates the luminous intensity (measured in candelas, cd) and illuminance (measured in lux) of a light source. The equation assumes the light source radiates a spherical matter.

E = I / R^2


E = illuminance
I = luminous intensity
R = radius of the sphere's light (meters)


HP 42S/DM42/Free42: Solver ILSPH

Code:

LBL "ILSPH"
MVAR "E"
MVAR "I"
MVAR "R"
RCL "E"
RCL "I"
RCL "R"
x ↑ 2
÷
-
END

Example:

Example 1:
Input: I = 10 cd, R = 2 m. Result: 2.5 lux

Example 2:
Input: R = 3.65 m, E = 30 lux. Result: I = 399.6750 cd

Sources:

Daryanani, Sital "Building Systems Design With Programmable Calculators" Architectural Record Books. McGraw-Hill Book Company: New York. 1980. ISBN 0-07-015415-5

Zumtobel "The Lighting Handbook" Zumtobel Lighting GmbH. Dornbirn, Austria. 6th Edition: 2018 https://www.zumtobel.com/PDB/Ressource/t...ndbuch.pdf

[Luigi Vampa]

I wasn't aware of the RCR. Thanks for sharing, Eddie.

[SlideRule]

This illustration
[attachment=7250]
may be helpful.

as well as Ligthing Design Calculations (20 pages): tables, illustrations, worksheets, charts etc.

BEST!
SlideRule

[Eddie W. Shore]

Thank you everyone!

Eddie