Case study #6: Energy Efficiency – Lighting Retrofit

Case Study #6: Energy Efficiency—Lighting Retrofit

** PROBLEM KEY ** Click Here for this RETScreen Case Study File [*.RET format]
Click Here for this RETScreen Case Study File [*.RET format]
The illumination level in a retail space has been measured and found to be 55 foot candles, which is equivalent to 600 Lux (a foot candle is one lumen per square foot, whereas the metric measure of Lux used by RETScreen is one lumen per square metre).

This illumination level is achieved by 30 incandescent light bulbs, each of 100 W. The bulbs are on 70 hours per week.

Electricity costs $0.10/kWh.


1)      What would be the energy savings associated with achieving this same lighting level with 30 screw-in compact fluorescent bulbs. (Hint: fix the number of bulbs and adjust the per bulb wattage until the same lighting level is achieved.)

2)      What are the annual energy cost savings?

3)      Can the illumination of 600 Lux be reduced? What is a typical illumination level for retail space?

4)      If an illumination level of 500 Lux were acceptable, and the same number of light bulbs were to be used (to maintain the visual pattern of the lighting), what wattage bulb should be used? If only 23 W bulbs were available, what would the level of over-illumination be (in percent above the 500 Lux target)?



  • Start by configuring the “Start Page” for this project. Remember that this is an energy efficiency project for a commercial building. It is not necessary to select a climate data location.
  • It is not necessary to specify any schedule information because this is for heating, cooling, and ventilation requirements only, and does not relate to lighting.
  • Click on the blue “Lights” hyperlink under “Facility Characteristics” to work with the building’ lights.
  • If a hyperlink doesn’t seem to work, try clicking on some other cell and then clicking on the hyperlink again.
  • RETScreen has two methods for working with lights—see the top right of the lights dialog box. One of these may be more useful than the other for this type of analysis.
  • Don’t know what an appropriate level of illumination is for a retail space? Try clicking on “Space Type” in the method 2 of the lights dialog box.
  • Don’t know how to enter 70 hours per week? Trying playing with the units switch for operating hours (yellow cell at the left).