HP 42S/DM42/Free42: Room Cavity Ratio, Luminous Intensity and Illuminance

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/example-of-role-surfaces-play-in-lighting-efficiency/  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

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.  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/teaser/en/Lichthandbuch.pdf

Eddie

All original content copyright, © 2011-2019.  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.

Retro Review: Halo HLC-1 Lighting Calculator

Retro Review:  Halo HLC-1 Lighting Calculator

HLC-1 Lighting Calculator

Years:  Unknown

Type:  4-Function, Lighting

Memory Registers: 1 (M)

Battery: A76

The Halo HCL-1 is a professional lighting calculator and a standard 4-function calculator. The standard 4-function calculator should be self-explanatory, let’s focus on the lighting part.

The HCL-1 is abundant on eBay, and make sure you get it with the foldout manual because (1) the manual is well written and (2) it explains the process in which pre-programmed calculations are completed.  I will show a short summary of some of the pre-calculations available below.

Trig table from the manual, something we don't see in calculator manuals

Did I mention that the manual contains a short table of sines and cosines?

US units are used (length is measured in feet).

Calculating Room Cavity Ratio:

Input:

Room Width in feet, [ RW ]

Rood Length in feet, [ RL ]

Room Cavity Height in feet, [ H ]

Output:

[ RCR ] calculates the Room Cavity Ratio

The HCL-1 assumes a rectangular room.  The formula:

RCR = (5 * H * (RW + RL)) / (RW * RL)

(Source:  https://algonline.org/index.php?gloss&glossaryid=232&glossarytitle=Room+Cavity+Ratio+(RCR , Advanced Lighting Guidelines web site)

Footcandle Calculation

Input:

Coefficient of Utilization, between 0 and 1, [ CU ]

Number of lamp lumens, [ LL ]

Required footcandles, [ FC ]

Output:

Press [ CAL ].  If successful, a 0 appears in the display.

[ RCL ] [ NUM ]:  number of adjusted luminaries (lights)

[ RCL ] [ FC ]:  number of adjusted footcandles

[ RCL ] [ A ]:  area that is illuminated

[ RCL ] [ SPG ]:  fixture spacing in feet

I am thinking that this solves where to put ceiling lights on the ceiling in a grid, like in a school classroom or business office.

You can factor in the lamp lumen depreciation factor ( [ LLD ] ) AND luminaire dirt deprecation factor ( [ LDD ] ).

Final Verdict

I am glad to have the HLC 1 in my collection.  It is one of the most unique calculators ever made and was met with amusement when I posted a picture of it on my Instagram account.  Don’t lose the manual. 

Eddie

This blog is property of Edward Shore, 2017