- No.406 HongTeng Building,
- 392# Xihong Rd,Gulou.
- Tel.: +86 591 6310 1956
- Fax.: +86 591 2285 5952
- E_mail : info@LEDaladdin.com
LED Light Guide Formulas
Simple Payback on an Investment (Years) = Net Installation Cost ($) ÷ Annual Energy Savings ($)
5-Year Cash Flow ($) = 5 Years - Payback (Years) x Annual Energy Savings ($)
Simple Return on Investment (%) = [Annual Energy Savings ($) ÷ Net Installation Cost ($)] x 100
Zonal Cavity Method (determining cavity ratios)
Room Cavity Ratio (for regular rooms shaped like a square or rectangle) = [5 x Room Cavity Depth x (Room Length + Room Width)] ÷ (Room Length x Room Width)
Room Cavity Ratio (for irregular-shaped rooms) = (2.5 x Room Cavity Depth x Perimeter) ÷ Area in Square Feet
Ceiling Cavity Ratio = [5 x Ceiling Cavity Depth x (Room Length x Room Width)] ÷ (Room Length x Room Width)
Floor Cavity Ratio = [5 x Floor Cavity Depth x (Room Length x Room Width)] ÷ Room Length x Room Width
Room surface reflectances can be predicted in a new design or measured in an existing facility. If existing facility:
Room Surface Reflectance (%) = Reflected Reading ÷ Incident Reading
Reflected Reading = Measurement from a light meter holding it about 1.5 feet away from the surface with the sensor parallel and facing the surface.
Incident Reading = Measurement from a light meter held flat against the surface and facing out into the room.
Calculating Number of Lamps And Fixtures And Spacing
Required No. of Fixtures = (Lumens/Lamp x No. of Lamps x Coefficient of Utilization x Light Loss Factor x Area in Square Feet) ÷ (Lumens/Lamp x Lamps/Fixture x Coefficient of Utilization x Light Loss Factor)
Required Lamps = Required Lumens ÷ Initial Lumens/Lamp
Maximum Allowable Spacing Between Fixtures= Fixture Spacing Criteria x Mounting Height
Fixture Spacing Criteria: See the manufacturers literature
Mounting height: Distance in feet between the bottom of the fixture and the workplane
Spacing Between Fixtures = Square Root of (Area in Square Feet ÷ Required No. of Fixtures)
Number of Fixtures to be Placed in Each Row (Nrow) = Room Length ÷ Spacing
Number of Fixtures to be Placed in Each Column (Ncolumn) = Room Width ÷ Spacing
For the above two formulas, round results to the nearest whole integer.
Spacingrow = Room Length ÷ (Number of Fixtures/Row - 1/3)
Spacingcolumn = Room Width ÷ (Number of Fixtures/Column -1/3)
If the resulting number of fixtures does not equal the originally calculated number, calculate impact on the designed light level:
% Design Light Level = Actual No. of Fixtures ÷ Originally Calculated No. of Fixtures
To calculate fixtures mounted in continuous rows:
Number of Luminaires in a Continuous Row = (Room Length ÷ Fixture Length) - 1
Number of Continuous Rows = Total Number of Fixtures ÷ Fixtures Per Row
Spot Relamping Cost
Average Annual Cost ($) = (Operating Hours/Year ÷ Rated Lamp Life) x (Lamp Cost + Labor Cost to Replace 1 Lamp) x Total Number of Lamps
Cleaning Cost ($) = Time to Wash 1 Fixture (Hours) x Hourly Labor Rate ($) x Number of Fixtures in Lighted Space
Average Reduced Air Pollution (lbs. Carbon Dioxide) = Energy Savings (kWh) x 1.6 lbs.
Average Reduced Air Pollution (g. Sulphur Dioxide) = Energy Savings (kWh) x 5.3 g.
Average Reduced Air Pollution (g. Nitrogen Oxides) = Energy Savings (kWh) x 2.8 g.
Pounds = Grams ÷ 454
Tons = Pounds ÷ 2,000
To learn more about for Technical information