| Cost of light The smallest part of the cost of light is actually the purchase price of the lamp, electricity accounts for 88% of the cost of light. By choosing a more efficient lamp, even one that costs more, you can save money over the life of the lamp. Electricity 88% Lamp 4% Labor 8% Comparing Efficiency and Life The following chart shows how incandescent, halogen, fluorescent and HID lamps compare in terms of efficiency and rated average life. Efficiency is measured in lumens per watt (LPW). Rated average life is the number of burning hours when 50% of the tested samples have failed and 50% are still operational. For both HID and fluorescent, lamp life depends on the number of hours per start. Typical LPW Rated Avg Life(hr) Incandescent 5-22 750-2000 Halogen 12-36 2000-5000 Compact fluorescent 27-80 9000-10000 Fluorescent 75-100 12000-24000+ Mercury 50-60 12000-24000+ Metal Halide 80-115 10000-20000 High pressure sodium 90-140 10000-24000+ I.E.S. Recommended Indoor footcandle level Footcandle level Office-corridors, stairways 10 Reading, transcribing 30 Regular office work 50 Residence-dinning area 15 Grooming area 30 Food preparation 75 Laundry 30 Study 50 General visual 7.5 Restroom 15 Stores-circulating area, stockroom 30 Merchandising, serviced 100 Merchandising, self-service 200 I.E.S. Recommended Outdoor footcandle level Min. footcandle level Parking area-Self parking 1 Attendant parking 2 Pedestrian Walkway-Commercial sidewalks 0.9 Commercial Pedestrian ways 2 Residential sideways 2 Residential pedestrian way 5 |