HP 42S/DM42/Free42: Room Cavity Ratio, Luminous Intensity and Illuminance
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
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/exampleofrolesurfacesplayinlightingefficiency/ June 16, 2010. Retrieved March 31, 2019
"Room Cavity Ratio, RCR" Illuminating Engineering Society. https://www.ies.org/definitions/roomcavityratiorcr/ 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
LBL "ILSPH"
MVAR "E"
MVAR "I"
MVAR "R"
RCL "E"
RCL "I"
RCL "R"
x ↑ 2
÷

END
Examples
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. McGrawHill Book Company: New York. 1980. ISBN 0070154155
Zumtobel "The Lighting Handbook" Zumtobel Lighting GmbH. Dornbirn, Austria. 6th Edition: 2018 https://www.zumtobel.com/PDB/Ressource/teaser/en/Lichthandbuch.pdf
Eddie
All original content copyright, © 20112019. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.
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
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/exampleofrolesurfacesplayinlightingefficiency/ June 16, 2010. Retrieved March 31, 2019
"Room Cavity Ratio, RCR" Illuminating Engineering Society. https://www.ies.org/definitions/roomcavityratiorcr/ 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
LBL "ILSPH"
MVAR "E"
MVAR "I"
MVAR "R"
RCL "E"
RCL "I"
RCL "R"
x ↑ 2
÷

END
Examples
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. McGrawHill Book Company: New York. 1980. ISBN 0070154155
Zumtobel "The Lighting Handbook" Zumtobel Lighting GmbH. Dornbirn, Austria. 6th Edition: 2018 https://www.zumtobel.com/PDB/Ressource/teaser/en/Lichthandbuch.pdf
Eddie
All original content copyright, © 20112019. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.
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