Energy Efficient Lights for Warehouse Applications
Efficient warehousing is an integral component of the supply chain strategy of businesses in a globally networked world. New technologies and material handling procedures are revolutionizing the warehousing world. Bar coding, radiofrequency tags, new packaging and efficient containers are changing the way goods are stored. Efficient warehousing and reduced supply chain costs are an integral part of the strategy of the likes of WalMart.
Lighting needs are responsible for half to three quarters of a warehouse facility’s lighting needs. Lighting was long considered an area in which costs were difficult to rein in. The only possible solution was to call the lighting contractor every couple of years to replace old inefficient fixtures. With LED lighting technology this circle is all set to change – after all the technology delivers 80% direct energy savings over incandescent technology and these lights will continue to be in service for a decade or more.
Light is needed in a warehouse to help in identifying workers and goods alike, reduce the risk of accidents and help in navigating aisles. Different areas of the warehouse are used for different purposes and may have varied lighting needs. A warehouse need not be a dark, dull and depressing area. With the right lighting technology it can be a comfortable haven for workers.
Cost of lighting warehouses
As a thumb rule, the cost of lighting a warehouse is around $1 per square foot per year. With energy efficient solid state lights based on cutting edge LED technology this lighting energy consumption can be reduced between 50 to 90%. For a 200,000 square foot storage facility lighting costs can fall from $200,000 per annum to as low as $ 20,000. Coupling these instant on, flicker free lights with intelligent lighting control systems can further help reduce lighting costs to $10,000. Light Emitting Diode based lights are solid state lights that are not affected by on-off cycling. They are therefore perfect for pairing with intelligent lighting control systems that provide real time, dynamic lighting level control. By any yardstick, the saving potential is substantial.
The US department of Energy estimated that solid state, Light Emitting Diode based lights can potentially help save 1,488 terra watts of electricity valued at $ 120 billion between 2010 – 2030. Simultaneously the green house gas emissions will come down by a stupendous 246 million tons. The report does not factor in the savings achieved by directionality of these lights or the fact that intelligent controls can further help businesses save money on lighting. The estimated additional savings from these two factors are estimated to be between 30 – 50%.
Lighting Design In Warehouses
Overhead lights are needed in loading areas for general illumination for better safety during loading procedures. Supplemental lights may also be needed to further improve illumination in certain cases. It is important to determine the lighting needs in each area and design lights accordingly. It is prudent to remember that something that cannot be measured cannot be controlled. At workstations low glare lights that enable office staff to comfortably read documents is needed. Good horizontal and vertical illumination is required for open storage areas as the aisles may be repeatedly reconfigured. Similarly good lighting is needed in rack storage areas. Besides these, lighting levels in a warehouse depend on the activity pattern, space design (open or confined), age and visual acuity of workers and size of items.
Recommended horizontal lighting levels range between 10 foot candles for inactive areas to as high as 50 foot candles in high activity areas where small items are handled. Good vertical illumination is needed to enable employees read labels. In general for an area that needs 10 foot candles of horizontal illumination 1 foot candle or more of vertical illumination (10:1 ratio) is generally recommended. It is not just the average lighting levels that are important – the minimum levels (3:1 ratio) are also important. Thus with an average illumination of 30 foot candles the minimum illumination should be 10 foot candles. The Illuminating Engineering Society of North America (IESNA) prescribes a set of guidelines for safe and comfortable lighting levels in warehouse facilities.
Lighting Options for Warehouses
When choosing the right lighting technology for warehouses a number of factors need to be considered.
Life time cost of lighting – These include onetime cost of lighting devices, energy costs, set up costs, replacement costs, cost of labor for replacement, cost of safe disposal of bulbs, cost of ordering and storage of replacement bulbs. If a warehouse believes in offsetting its carbon foot print the cost of carbon emitted must also be factored in. Some experts believe that in keeping with the triple bottom line approach to business, other environmental and social costs of lighting should also be calculated. On each one of these LED lighting trumps the competition.
Cost of replacements
LED lights have a phenomenally long life. Each LED device can last up to 10 years or more. Businesses relying on alternate lighting devices will need 50 incandescent bulbs or 12 CFLs for a single fixture during the same period. Cost savings in maintenance Here is the cost of replacement for a single light fixture Activity Time in minutes 1. Staff documents light failure and places a call to maintenance personnel 10 2. Logging the call and scheduling 5 3. Arranging replacement lamp and ladder 10 4. Reach location of light failure and Replace lamp 10 5. Dispose burnt out lamp, replace equipment and log details 10 Total time taken 45 minutes.
At an average labor cost of $ 16 per hour each replacement would cost $12. If an outdoor light needs replacement the cost will be higher as a truck or special ladder may be needed to access lighting fixtures and more than one personnel may be involved.
Clearly the long life of lights is an important component of the total cost of ownership. The annual replacement costs for incandescent will reach $ 60 per annum while the same figure for fluorescents will be $12.
Efficiency or light output per watt – Lumens or foot candles per watt is a measure of the energy production efficiency of a lighting device. A drawback of this measure is that it measures the light produced by the bulb. It does not consider how much of the light produced by the bulb is wasted. LED light bulbs produce directional light as opposed to other light sources – far fewer lumens are needed to illuminate the target area. Measuring lumens achieved at the surface of interest are a much better measure of lighting efficiency.
Light distribution – High shelves can cause unwanted shadows on the floor. Using fewer but high power lights can provide the required illumination but will lead to glare making life uncomfortable for workers. The logic behind using high power lights is that there are fewer light fixtures to service. With LED bulbs and tubes that last a decade or more this logic is now defunct. Many smaller lights can now be placed in the warehousing facility to achieve uniform light distribution and effective control without sending the maintenance costs out through the roof.
Light color rendering index (CRI) – Good color rendering index lights improve the appearance of goods and make it easier to distinguish between instructions printed in different colors. Poor CRI sodium vapor lights are generally not preferred partly because they may make everything look a sickly shade of yellow and partly because of the effect on motivation that long term exposure to sickly pale light can have.
Lamp lifetime – Lamp lifetime is not just about the day the lamp will stop burning. The end of useful life is what facility managers are worried about. Warehouse managers therefore look at how well lumens are maintained over the life of a lighting device. Solid state, Light Emitting Diode based lights maintain the lumen output well over their life time. Since each light is a cluster of diodes the possibility of all of them failing simultaneously is also remote.
Some of the lighting options and their properties are:
Mercury vapor lights - have poor color rendering index and low light output per watt. -High pressure Sodium lamps – have a lamp life of 12,000 hours, poor color rendering index but good raw lumens output. One of the most common uses for these lights was in open parking areas where color discrimination is not important. However even in this application Sodium lights are losing to better and more economical lights based on LED technology.
Metal halide lamps – have a lifetime of 12,000 - 15000 hours and good color rendering properties. They are expensive compared to other HPS light sources.
Fluorescent tubes and CFLs – generally used for lighting indoor spaces these are not suitable for low temperature operation making them unsuited for use in cold climates and in cold store locations. The problem of mercury contamination and short life span (compared to LEDs) also dog these lights.
LED lights – the last word in lighting efficiency. They produce high CRI directional light. The lumens achieved at desired points are therefore better. In energy efficiency these lights are incomparable. A 34 watt LED fixture can replace alternate lighting devices using as much as 445 watts of electricity. Lamp life is generally 30,000 hours or more. An added plus is that these lights are not affected by on off cycling and are amenable to control by intelligent systems further increasing the possibilities of energy savings.
Most HID lamps that are used in warehousing facilities do not achieve full brightness instantly and have significant warm up times. Some HID lights also have an extended re-strike time (the lamp must be allowed to cool before it can be switched on again). This severely curtails the possibility of using occupancy sensors and other intelligent control systems.
Some of the issues that will need consideration when designing warehouse lighting or determining the right lighting fixtures are: -Frequency with which the warehouse space is used. -Uniformity of use. Intelligent controls will produce better results when used in areas that are not used as frequently.
Cost of maintenance – should include the cost of replacement, labor and equipment charges and the cost of disruption of business activities. -The desired temperature of the store. For cold temperature storage facility – Light emitting diode based lights that produce less heat are highly -desirable for cold temperature applications. According to WalMart these lights deliver more than 80 % return over fluorescent lights.