Lighting Design Calculations by Using Excel Spreadsheets – Part One


In the previous articles in this course “ Advanced Course for Lighting Design - Level I ", I explained the lighting design calculations by using (4) different methods in the following articles: 

  1. Lumen (Room Cavity) method - Part One
  2. Lumen (Room Cavity) method - Part Two
  3. Point by point method,
  4. Watts per square foot method.

Also, I explained lighting design calculations by using CalcuLux Indoor software in the following articles: 


And I explained also the easy manual for lighting design calculations by using DIALux software in the following articles:



Today, I will explain the lighting design calculations by using excel spreadsheets as follows.



First: The GE Lighting Assistant 3.0



These tools developed by GE to provide an analysis of a lighting system and are meant to assist users in reviewing certain lighting options. To perform an analysis, the tools make certain assumptions based on a variety of factors as shown in below.



The GE Lighting Assistant 3.0 includes the following tools:
  1. Cost of Light Tools 
  2. Lamp Performance 
  3. Group Relamping 
  4. Selling Aids 
  5. Energy Policy Act 
  6. Lighting Layouts 
  7. Retrofit Options 
  8. Scotopic Photopic 
  9. Internet Links 
  10. Other Tools 



1- Cost of Light Tools


This tool has sub-tools as follows:

1.a Simple Energy Estimator


This tools calculate the energy used and energy saved with a potential upgrade. Put in the watts of the existing and proposed lamps and this tool will show the customer how much they are spending on energy and the energy savings available.

Also calculate a payback based purely on energy savings.



1.b Fixture Wattage Tool

Lighting designers complains that there was no way to find out fixture wattage to put in the various lighting calculators

For example, what is the wattage of a 2-lamp F32WM fixture on a high ballast factor UltraMax ballast?

The fixture wattage tool was designed to arrive at approximate wattage numbers with a few clicks and they can Use this number in the energy savings calculations.





To use this tool, Click on the Lamp types to obtain input watts to typical systems.

Note: For incandescent, halogen and screw-in CFL simply use the lamp wattage.



1.c Investment Calculator

Tracks all the expenses involved and tabulates and calculates the total investment needed to carry out the suggested upgrade.



1.d Simple Payback Calculator


One step beyond the Simple Energy Estimator, this tool allows you to include A/C savings and labor/maintenance savings to get a truer payback estimate.



1.e Motion sensors and Dimming


Dimming systems and motion sensors are becoming more common.

This tool shows you how estimate energy savings in these situations.



1.f Life-Cycle Cost


When comparing systems with very different lamp life (e.g. incand. versus CFL) lifecycle costing provides a quick comparison of the average costs of owning and operating a system.



1.g Cost of Waiting


Postponing the lighting upgrade is costing your customer money! Let this tool show the customer how much it is costing him per month and how much per year! Light a fire under them! Move them to action!



1.h Environmental Impact Estimator


Determine the typical impact a Lighting upgrade has to the environment – Carbon Dioxide Reduction - as it relates to added new forests or reducing cars.





2- Lamp Performance


This tool has sub-tools as follows:

2.a Hi-Calc (Inc-Hal Life Estimator)


Using a 130 volt lamp on a 120 volt socket will extend lamp life – How much? and what other effects does it have on the lighting? Just fill in the numbers and this calculator will show the the rest.



2.b System Lumen Comparisons


An excellent tool that graphically compares the light output of any three alternate systems over life e.g. HID vs. T5 vs. T8.



3- Group Relamping 


Compare group relamping with spot relamping. And find the optimal group relamping point



4- Selling Aids


This tool has sub-tools as follows:

4.a Cross- Reference Tool


Find the product that replaces a competitive part—OSI, Philips or TCP?

This tool has it!



4.b Sales Opportunity Estimator!


You just drove by a multi-story office complex the other day?

Quickly estimate how many lamps, ballasts and fixtures are in the building.



4.c Lighting and Productivity


A small increase in productivity or retail sales can justify almost any lighting upgrade! Use this tool to talk to customers about these benefits!



4.d Equivalent Sales Increase


Demonstrate the added value of energy saving by stating the equivalent sales increase a company would need to achieve the same bottom line results.



4.e Lighting Cost Per Employee


Help owners realize how little they are spending on lighting and lamps!



5- Energy Policy Act


This tool has sub-tools as follows:

5.a TAX Incentive Calculator


Tool allows you to provide your customers with a simple review of the potential Tax Incentive as it relates to their installation. Helps calculates light levels and energy savings while satisfying power density limits.



6- Lighting Layouts


This tool has sub-tools as follows:

6.a Fixture Count Estimator





This tool allows you to estimate the number of fixtures it would take to light up an area to a desired footcandle level.

A key number of calculations is the coefficient of utilization CU. typical CU ranges from 50% to 70% depending on the efficiency of the fixture, the reflectance of walls, floor and ceiling, etc… for a first pass a value of 0.6 (60%) should be used

Note that this tool asks for the mean rated lumen of the lamp, not the initial lumens. Some professional software use the initial lumens and the use of a “ light loss factor” which includes lumen depreciation and other factors like dirt depreciation, light reduction from voltage fluctuation and temperature effects, etc…

In this tool CU number is meant to include booth CU and light loss factor, and so on an appropriate adjustment can be made if these light loss factors are considered to be significant.

To use this tool, Input your data in the green cells and The outputs data will be shown in the yellow cells.

Note: this is a useful estimator, but the final layout should be done with professional software.



6.b Footcandle Estimator





Estimate the footcandle level achieved when an area is lighted with a given number of fixtures. This tool is the reverse of the Fixture Count Estimator.

The difference between fixture count estimator and footcandle estimator is that the footcandle estimator tool estimates the light level given a certain numbers of fixtures, while that fixture count estimator tool estimates the number of fixtures required to achieve a given light level in a space.

To use this tool, Input your data in the green cells and The outputs data will be shown in the yellow cells.



6.c Watts Per Square Foot





Estimate the watts per square foot contribution from two different lighting scheme. If several overlapping systems are present in the same space: general lighting, track lighting, task lighting, etc., their individual watts per square foot must be added.

Many codes and regulations attempting to limit energy consumption by specifying upper limits on watts of electricity used per square foot of area space to illuminate the space (e.g. 1.6 watts per sq. foot).

Also, this tool allows a simple comparison of two alternative lighting schemes to be used in a space.

Note: Note that there are complex specifications when it comes to track lighting, dimming systems and motion sensors and a thorough understanding of the code is necessary for a professional evaluation.


Watt per square foot tool includes three different sheets as follows 

6.c.1 Understanding Lighting Layout
Figure explain the main definitions in lighting layout.

6.c.2 Suggested Lighting Levels
Table list the recommended footcandels by IESNA as follows:





6.c.3 Representative CU’s (INFO)
Table of representative CU’s of various fixtures that allows lighting layouts to be estimated more realistically






7- Retrofit Options


This tool has sub-tools as follows:

7.a Upgrade Options by Fixture


Look up in the ceiling and see a lighting fixture. Use this tool visually to click on the fixture you see; follow the links to see what lamps are commonly used in this fixture and what upgrade opportunities are available


7.a.1 Value added listing


Table includes existing lamps, desired features and upgrade options with notes. 


7.b Fixture Replacement


Figure out how many fixtures with Lamp B can replace the fixtures with lamp A while maintaining the same light levels.


7.c System Lumen Comparisons


An excellent tool that graphically compares the light output of any three alternate systems over life e.g. HID vs. T5 vs. T8.



7.d Retrofit Options Analyzer


Compare the existing lighting scheme with up to three different alternatives; obtain light levels, watts per sq. ft. and energy costs per year for the different options



7.e New Installations Options Analyzer


Compare up to four different schemes for lighting a new area, obtain light levels, watts per sq. ft. and energy costs per year for the different options.



7.f Highbay Performance Comparison


This tool that facilitates the examination and discussion of different options for industrial high-bay lighting.



8- Scotopic Photopic


8.a S/P Tables for Light Sources


Included is a one page summary of the great (S/P) ratio debate (!) and tools to estimate (S/P)n for any lamp and any n and also a tool for comparing lighting layouts done using the (S/P) ratio.



9- Internet Links


With an internet connection you can easily go to many useful pages on GE Lighting’s Web Site. Retrieve customer testimonials, spectral curves of lamps or activate an interactive Color Booth with one click!

Internet links includes:

  • Product Catalog 
  • Glossary of Terms 
  • Application Brochures 
  • Product Brochures 
  • Sell Sheets 
  • Testimonials 
  • Color Booth 
  • More internet links 



10- Other Tools

10.a Value*Light


Value*Light is GE’s award winning Cost of Light analysis program. A sophisticated customer requiring advanced financial analysis and cost justification will love the report that Value*Light will provide!



10.b LightPro


Light Pro is a first-level training package for Lighting Professionals. All basic information about lamps, ballasts and applications can be obtained in an easy-tounderstand format by clicking on this link.





How to use The GE Lighting Assistant 3.0 for lighting design calculations?


to use 
use The GE Lighting Assistant 3.0 for lighting design calculations, Review the above paragraphs for important items which are: 

  • Fixture Wattage Tool 
  • Fixture Count Estimator 
  • FootCandle Estimator 
  • Watts per square foot 
  • Suggested light levels 
  • Representative CU’s (INFO) 


Free Download:

you can download your free copy of GE Lighting Assistant 3.0 by Clicking on the link.



In the next article, I will explain Another excel spreadsheet for lighting design calculations. Please keep following.



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