Be conscious, though, that skylighting also brings occasional sunlight with it and that’s something that ought to be avoided. Solar gain can aggravate internal temperatures in a shed structure, and direct sunlight onto packaging could be damaging. Oh, yes, and rooflights can be a great escape route for heating in the winter months. These environmental issues are resolved by having rooflights fitted with solar glazing. Look for a glazing system that incorporates solar control that reduces direct sunlight into the building and also offers low heat emission, so that less heat can escape by that route.
Warehouse sheds tend to be high structures, with plenty of height for vertical storage, triple-tier shelving being typical. But the closer your storage gets to the roof, the more lighting you will need. If your aisles are like canyons then you must have lighting that is dedicated to the aisle layout; there’s no point thinking that a light fitting mounted directly above a bank of shelving is doing any good at all. The rule of thumb is that a lighting installation that is dedicated to an aisle layout will be more expensive than an installation that provides overall illumination, but the added cost has to be offset against the greater storage efficiency achieved by multiple storage tiers.
Lighting fixtures should be placed above the tallest rack or pallet for the best lighting distribution—which may make the case for using a low profile luminaire. Low profile luminaires may also be better suited to environments where forklifts are used to move merchandise so the forklift masts do not strike and break the luminaires.
If you’re prepared to make holes in your roof, then there is a free light source available for at least half of the working year. Rooflights make a huge difference to the cost of lighting for warehouses. Obviously, there is a cost to installing them and they will require some maintenance – and you may want to check your insurance cover against potential weather damage if one of them fails, but, generally speaking, rooflights are a good thing.
A poorly illuminated warehouse is an environment ripe for errors. Most warehouse facilities have a variety of functions performed within their walls—from picking operations and packaging to shipping and receiving, light assembly and even office work. These multiple tasks make lighting design a challenge because more than one task may be performed within the same area, requiring different light levels.
Fluorescent systems may be wired with multiple switching so that the luminaires within a certain area can be turned on and off as needed. This capability increases the system’s flexibility and allows the facility to take advantage of skylights and daylight harvesting to reduce operating costs.
Case study: How OZtrail warehouse saved 60% energy with LED high bays
If glare is a potential problem, consider using enclosed HID luminaires or a fluorescent system with a bottom lens. Installing luminaires with an element of uplight will also help reduce glare.
Fluorescent systems operate cooler than HID luminaires. The higher the wattage lamps, the more heat an HID system will produce, which could lead to higher HVAC costs. If a facility’s air conditioning costs are unusually high and the lighting system uses high wattage lamps, the system may be retrofit with fluorescent luminaires or lower wattage HID lamps to reduce the operating costs.
There are three light sources that are currently in use for warehouse lighting. Let’s start with the one that’s likely to disappear first. Metal halide light sources were the success story of the 1990s. The lamps improved in their colour rendering, more wattages became available and the lamp changed its shape, meaning that a whole new generation of high-bay lighting was created. But everything that the metal halide lamp delivered can now be provided by LED lighting, with the important addition that LED sources can be dimmed. Despite attempts to dim the metal halide lamp, the idea never caught on and in these energy-conscious times, that is likely to mean the death knell for the metal halide lamp.
Part of the assessment of how the warehouse functions should be a review of how the building actually works. It may be that it’s not necessary to illuminate the entire building for the entire time. Lighting controls are becoming a regular component of aisle-lighting schemes. If there is no one in an aisle, then the lighting automatically drops to a lower level, reducing energy spend.
Contrast and the size of objects involved in a task will also influence the light levels required. Tasks are easier to see when the contrast between an object and its background is greatest. For example, black lettering on a white label will have a higher level of contrast than dark blue lettering on a medium blue or medium gray background. Higher illuminance will help compensate for poor contrast and smaller objects.
Good warehouse lighting should be at the heart of a consumer economy and there are sound financial reasons why companies should see the investment in their warehouse environment as being very good for their bottom line.
Pulse start metal halide lamps are the most efficient metal halide lamps on the market. They not only provide the light levels needed, but they offer more light over the life of the lamp. A pulse start lamp will produce 110 lumens per watt (LPW) compared to 80 LPW provided by a standard metal halide lamp. Pulse start metal halide lamps also warm up faster to full brightness and have quicker restrike times. Although pulse start lamps cost more initially than conventional metal halide lamps, warehouse owners and managers benefit from lower installation, operating and maintenance costs (See Figure 1).
Don’t be tempted by the cheapest light fittings on offer; they may come at an unexpected price. The new generation of LED high-bay lighting are reporting extraordinarily high efficacv figures in terms of the amount of light that gets delivered per Watt. But those figures need to be considered alongside the way that the light is delivered. Crude optics that ensure as much light falls out of the face of the fitting as possible may be a hazard to staff if glare becomes a problem. Coming back to high-level shelving, fork-lift operators need to have clear sight of their surroundings and that includes especially the shelves’ upper regions. Looking up into the face of a super-brilliant light fitting is a problem, and it could become a dangerous one.
Summary Warehouse managers, owners and designers have a variety of options when selecting the lighting system for a warehouse environment. But, no matter what type of system they choose, lighting uniformity is essential. A uniformly illuminated environment will not on promote worker safety but will improve performance. An efficiently illuminated facility will also impact the bottom-line.
Luminaire placement will affect lighting uniformity. Warehouse managers typically try to get the most use of the space they have within their facilities. For example, if the ceiling height is 30 feet, products in the racks or on pallets may be stacked to within a foot of the ceiling. Mounting the luminaires in the middle of the aisles instead of directly above the racks or pallets will minimize shadows and will help assure maximum lighting uniformity.
But, in applications where employees are doing light assembly work or boxing product, color identification may be essential. Color rendering is the ability of the light source to represent the true colors in an object. The closer the color rendering index (CRI) is to 100, the more natural product colors will appear. The CRI of metal halide lamps is 65, with HPS lamps at 20. The CRI for fluorescent lamps is 80.
Facilities management is looking at the use of electronic reporting to keep better control on the energy management of commercial and industrial buildings, so we can expect to see more use of lighting control systems being linked to BMS (BuIlding Management Systems) and BIM (Building Information Modelling) software.
Providing an element of uplight will help create a more uniform environment. Most glass luminaires will provide 15 to 20 percent uplight, which illuminates the ceiling and eliminates the cavern effect that can occur when a ceiling is dark. With a white or light colored ceiling, uplight will bounce off the ceiling to create a more uniformly illuminated environment.
Rooflights make a huge difference to the cost of lighting for warehouses. Use free light
The light levels and visibility required within a warehouse will depend upon a number of factors, including the tasks performed, the age of the workers and the type of space—whether it is an open space or has racks. The more active the area—such as a loading dock or staging area—the higher the light level requirements. Illumination levels will also be affected by the size of the items that are being handled. For example, an active area with small items (and small labels on containers) will require 20 to 50 footcandles on average. An active area with large items will require only 10 to 20 footcandles. An inactive area, such as a cold storage facility, will require only 5 to 10 footcandles.
There is no money to made out of warehouse lighting. It’s just a cost that companies need to bear because, after all, warehouses are a necessary burden to the business, so let’s just keep it tight and expenditure to a minimum, right?
The best way to determine the required horizontal and vertical illumination levels is to consider the average to minimum ratios. The horizontal average to minimum ratio for a rack area should not exceed 3:1. If the average light level in an aisle is 20 footcandles (fc), the minimum horizontal levels should be 6.7 fc or greater. The vertical average to minimum ratio for this same area should not exceed 10:1. This means that if the average footcandle level is 15, the minimum vertical footcandle level should never be less than 1.5 fc.
Light levels will be affected by the reflectance of surfaces within the facility, such as the walls, ceiling, floor, racks, pallets and containers. A black or dark colored wall or ceiling will not be as reflective as a white wall. For example, a space with two brown walls and two white walls may require six luminaires to provide the light levels required. The same space with four white walls will require only four luminaires. Keep in mind that shiny metal racks will reflect light while brown-colored boxes and other containers will absorb light.
Picture: courtesy of Daviid Thrower, Redshift Photography/Holophane/Travis Perkins
Flicker of LED sources is becoming the surprise issue of recent months. Perhaps this is to do with the burgeoning LED market and less than scrupulous manufacturers taking advantage of ultra-cheap components, but flicker can be a disabling problem and if you are putting staff into an environment where 100% of the illumination is coming from an inferior source, then expect absences, illnesses, poor performance and, eventually, a writ.
Fluorescent systems also offer the advantage of “instant on.” All HID systems have a warm up time. During a power surge or outage, for example, a standard metal halide luminaire will require 10 to 15 minutes to cool down, plus an additional five to seven minutes to heat up. Fluorescent systems, on the other hand, will re-light immediately.
The age of the workers is another consideration when determining the light levels needed. As workers grow older, they require more light to compensate for degraded vision and the decreased size of the pupil. Attaining retinal illuminance for older workers equal to that of younger workers requires greater luminance on the task. (See Figure 2).
Good lighting is essential in a warehouse to promote worker visibility, safety and performance. An efficiently illuminated facility will also reduce operating costs, which will impact the bottom-line.
Many warehouse owners and managers tend to prefer the white light provided by metal halide or fluorescent systems. Even though the measured footcandles may be nearly the same as for an HPS system, employees believe they can see better under a metal halide system because the environment appears brighter.
Efficient, long-lasting lights that turn off when they’re not needed – warehouse lighting’s simple, really
The above recommendations refer to the work plane. In warehouses, this is likely the vertical stack surface, and at times, the horizontal at document reading height. Adequate levels of vertical illumination are essential to read the labels on cartons, read signs within the facility (including exit signs), and to drive a forklift.
Whether the application is a new facility or a lighting retrofit, the question often arises as to what type of lighting system is best—a high intensity discharge (HID) system or fluorescent.
Also, more luminaires are being fitted with self-checking circuitry that can report back to a central monitoring system if a fault occurs within the fixture. And with the advent of new technologies such as Li-Fi (Light Fidelity), where digital information can be transmitted to hand-held devices via an LED lighting installation, we can expect to see logistics management taken to exciting new levels.
The latest in LED high-bay warehouse lighting: The Holophane Haloprism
Design guides exist to let you know what the recommended lighting levels are for warehousing. Those lighting levels are based on the level of detail that’s expected from staff. If your pickers are under pressure to satisfy intense daily delivery schedules it would help them, and help the business, if they have enough light to read labels easily and without squinting to see whether that ‘3’ is actually an ‘8’.
Spending as little as possible is a fool’s errand. The less that gets spent on lighting, the more will get spent on dealing with returns, damaged goods, staff turnover and general incompetence. It’s because warehouse staff would prefer to be able to see what they’re doing and to be able to read the label on the box.
Well – it all depends on how efficient a business expects its distribution network to be. With ‘logistics’ being the buzz word on everyone’s transport fleet, it’s probably worthwhile giving a bit more attention to the quality of service that goes on inside those huge sheds.
The down side of fluorescent systems is that they are heat sensitive. A fluorescent system may not be suitable for a warehouse in Texas that has no air conditioning during the summer.
Lighting uniformity within a warehouse space is essential. Forklift drivers and others must be able to look up and down the stacks of product without constantly having to adjust their eyes. The human eye functions more comfortably and efficiently when the luminance within the field of vision is fairly uniform.
Lux is also hosting a special Lighting for Logistics and Warehousing conference in Amsterdam on Friday 30 September. It’s free for all those involved with the management of of storage and distribution.
To view the details and register for a place, click on the conference logo here.
Controls Lamps may burn constantly in areas that are continually in use. However, in peripheral aisles that are used only part of the time, warehouse operating costs can be reduced by turning HID lamps to lower levels when a space is unoccupied—or turning the fixtures off completely. A bi-level switching system may be installed to reduce the input wattage by 50 percent for metal halide lamps, or 35 or 50 percent for high-pressure sodium lamps.
A luminaire’s distribution pattern will contribute to a system’s uniformity. Fluorescent fixtures or HID luminaires with an asymetric (long and narrow) pattern are best for aisleways, whereas luminaires with a symmetric pattern are more applicable for open storage and shipping areas. In open areas where multiple tasks are performed, the ambient lighting may need to be supplemented with additional fixtures. For example, in an open storage space where light assembly is performed, supplemental fluorescent luminaires may be installed directly above the task to boost the light levels.
The source that is holding out against the march of the LED is the fluorescent tube. The latest generation of T5 tubes (16mm diameter) demonstrate an efficiency that the LED has struggled to better. Though it’s probably only a matter of time before that stops being the case – and it may already have happened by the time you read this, the T5 fluorescent lamp is a very good source for warehouse lighting. Aisle schemes, in particular, work well as the sideways distribution from the fluorescent source often outperforms the LED equivalent, making it a more effective source for high shelving.
The rule of thumb is that a lighting installation that is dedicated to an aisle layout will be more expensive than an that provides overall illumination
If efficiency is the primary concern, a high-pressure sodium (HPS) system is the most efficient light source available, providing the most lumens per watt. HPS lamps have a longer life than standard metal halide systems, which translates into lower maintenance costs.
Of course, the LED has taken over in almost every lighting sector. It is a very efficient source, and continues to get ever brighter. A good LED luminaire will hold its own against any other type of fixture, but it’s a technology that comes with a warning. Too much of a good thing can be bad for you. LED sources, as mentioned above, can create a level of glare that makes a job difficult and uncomfortable. That glare comes from two possible sources; either because the optical control of the luminaire isn’t very good, or because, quite simply, the LEDs are too bright. There has to be a balance between the light from a luminaire and the comfort of the people working under it.
We’re used to the idea that lighting installations can be fitted with daylight linking so that maximum benefit is made of the available light, but the world of lighting control is moving far beyond that.
However, many warehouse owners and managers are reluctant to use HPS systems because of the lamps’ yellowish color. In warehouse applications where storage, shipping and receiving are the main functions, color may not be an issue.
New luminaire and lamp technology has also made fluorescent systems better suited to warehouse environments. The new systems provide the illumination levels needed in facilities with higher ceilings and they use less energy than a metal halide system. For example, one 400-watt metal halide high bay fixture may be substituted with six 32-watt fluorescent fixtures for a total wattage of 192 vs. 400 (not including ballast losses).
And if you’re lucky enough to have an automated picking process that doesn’t require the human touch, and so requires very little lighting, remember that the robots will also need some TLC occasionally. So a maintenance lighting installation, even if used only occasionally, would still get the job done more quickly than hauling temporary lighting around.
Lux is hosting a special Lighting for Facilities Managers conference in London on Wednesday 19 May. It’s free for all those associated with the management of buildings services. To view the details and register for a place, click on the conference logo here.