When installing new lighting, or refurbishing an existing scheme, it is important to quantify and compare the benefits of possible alternative replacement lighting systems. These benefits are quantified in terms of a life cycle calculation for each lighting system, that is over the planned life of the installation how much will each system cost. These values can be compared and the most favourable option chosen. (Note that the most favourable option from a financial viewpoint may not be the best option from a lighting viewpoint. At some point a decision will have to be made as to the relative importance of these factors and a compromise reached).
If the chosen system is to be a replacement for an existing installation a cost benefit of the new system compared to the existing installation may be made by calculating the pay back period, as shown Section 7.2.
Worksheet 7.1 aids life cycle analysis. Formulae used is this worksheet are:
(Note that the model given on the following page is a static model in that it ignores the costs of depreciation of equipment and interest payments).
Luminaire costs = Number of luminaires x cost of one luminaire
Lamp costs = number of luminaires x number of lamps per luminaire x cost of one lamp Installation costs = number of luminaires x installation cost per luminaire Room cleaning costs = cost of room cleaning x service life of system (years)
room cleaning interval (years)
Luminaire cleaning costs = cost of luminaire cleaning x service life of system (years) luminaire cleaning interval (years) Lamp replacement costs = cost of lamp replacement x service life of system (years)
lamp replacement interval (years)
Energy costs = (number of luminaires x system power of luminaire x service life of system x annual burning hours x energy cost per kWh x %energy savings due to controls)/1000
Operating costs = room cleaning costs + luminaire cleaning costs + lamp replacement costs + energy costs Annual operating costs = operating costs/service life of system
Luminaire type (1) Luminaire data
Number of lamps per luminaire (2)
System power of luminaire (W) (3)
Operating data
Service life of system (years) (4)
Annual burning hours (5)
Lamp replacement interval (years) (6)
Luminaire cleaning interval (years) (7)
Room cleaning interval (years) (8)
Number of luminaires
Lamp lumens maintenance factor (9)
Lamp survival factor (10)
Luminaire maintenance factor (11)
Room surface maintenance factor (12)
Maintenance factor [ (9)x(10)x(11)x(12) ] (13)
Number of luminaires (14)
Itemised investment costs
Cost of one luminaire (15)
Cost of one lamp (16)
Installation costs per luminaire (17)
Itemised operating costs
Cost of lamp replacement (18)
Cost of luminaire cleaning (19)
Cost of room cleaning (20)
Energy costs per KWh (21)
%Energy savings due to control system (22) Investment costs
Luminaire costs [ (14)x(15) ] (23)
Lamp costs [ (14)x(2)x(16) ] (24)
Installation costs [ (14)x(17) ] (25)
Investment costs [ (23)+(24)+(25) ] (26) Operating costs
Room cleaning costs [ (20)x(4) / (8) ] (27) Luminaire cleaning costs [ (19)x(4) / (7) ] (28) Lamp replacement costs [ (18)x(4) / (6) ] (29) Energy costs [ (14)x(3)x(4)x(5)x(21)x(22) / 1000 ] (30) Operating costs [ (27)+(28)+(29)+(30) ] (31)
Option 1 Option 2
Checklists
7.2 Economics
When refurbishing an existing installation it is important to be able to quantify the benefits of the new lighting system compared with the existing system. These benefits are quantified in terms of the payback period. This is a comparison of the expenditure in terms of investment costs to buy and install a new system, compared with the savings in annual operating costs through having the new system. Thus if a payback time is 5 years this means that after 5 years the savings from using the new system have cancelled out the costs of buying the new system.
Worksheet 7.2 aids in the calculation of this value. Formulae used is this worksheet are:
(Note that the model given in Worksheet 7.2 is a static model in that it ignores the costs of depreciation of equipment and interest payments).
Luminaire costs = Number of luminaires x cost of one luminaire
Lamp costs = number of luminaires x number of lamps per luminaire x cost of one lamp Installation costs = number of luminaires x installation cost per luminaire
Room cleaning costs = cost of room cleaning x service life of system (years) room cleaning interval (years)
Luminaire cleaning costs = cost of luminaire cleaning x service life of system (years) luminaire cleaning interval (years)
Lamp replacement costs = cost of lamp replacement x service life of system (years) lamp replacement interval (years)
Energy costs = (number of luminaires x system power of luminaire x service life of system x annual burning hours x energy cost per kWh x %energy savings due to controls)/1000
Operating costs = room cleaning costs + luminaire cleaning costs + lamp replacement costs + energy costs Annual operating costs = operating costs / service life of system
Pay back period = investment cost proposed installation – investment cost existing installation annual operating costs existing installation - annual operating costs proposed installation
Luminaire data
Number of lamps per luminaire (2)
System power of luminaire (W) (3)
Operating data
Service life of system (years) (4)
Annual burning hours (5)
Lamp replacement interval (years) (6)
Luminaire cleaning interval (years) (7)
Room cleaning interval (years) (8)
Number of luminaires
Lamp lumens maintenance factor (9)
Lamp survival factor (10)
Luminaire maintenance factor (11)
Room surface maintenance factor (12)
Maintenance factor [ (9)x(10)x(11)x(12) ] (13)
Number of luminaires (14)
Itemised investment costs
Cost of one luminaire (15)
Cost of one lamp (16)
Installation costs per luminaire (17)
Itemised operating costs
Cost of lamp replacement (18)
Cost of luminaire cleaning (19)
Cost of room cleaning (20)
Energy costs per KWh (21)
%Energy savings due to control system (22) Investment costs
Luminaire costs [ (14)x(15) ] (23)
Lamp costs [ (14)x(2)x(16) ] (24)
Installation costs [ (14)x(17) ] (25)
Investment costs [ (23)+(24)+(25) ] (26) Operating costs
Room cleaning costs [ (20)x(4) / (8) ] (27) Luminaire cleaning costs [ (19)x(4) / (7) ] (28) Lamp replacement costs [ (18)x(4) / (6) ] (29) Energy costs [ (14)x(3)x(4)x(5)x(21)x(22) / 1000 ] (30) Operating costs [ (27)+(28)+(29)+(30) ] (31) Annual operating costs [ (31) / (4) ] (32)