What is Average Rated Life of a Lamp or Bulb?
In lighting parlance, the Average Rated Life (ARL) of a lamp or a bulb refers to the time it takes for exactly half the bulbs (50 percent) of a test sample to die out while the other half continue to burn. The ARL of a light bulb is also popularly known as half-life. It is expressed in hours and is an indicator of the longevity of lights.
You should know how the average rated life of a lighting device is calculated and the conditions under which these are tested to choose lights that are suited for your business and last long enough to help you make the most of your investment in your lighting infrastructure. On the other hand, knowing about the testing conditions will help you simulate these at your workplace so that the lights you buy reach the ARL stated for them.
What can You Make Out from the ARL of a Lighting Device?
Consider this example. 10 light bulbs are tested and found to have an ARL of 1,000 hours. This means that 5 (or 50%) of these bulbs had died by the time 1,000 hours had elapsed. Some of these bulbs may have died early, say just after being switched on for 50 hours, while some others may have lasted for 1,500 hours. But the ARL indicates that half of the total number of bulbs tested die out within 1,000 hours.
In this case, it is worth clarifying that the life expectancy of each individual light bulb or lamp cannot be predicted. The ARL is an adequate indicator of the average lifespan of a group of light bulbs or lamps. Some light bulbs burn out before reaching the average life span indicated for them while there are also some lights that last longer than the ARL for their batch.
What are the Testing Conditions for Determining the ARL of Lights?
Tests to determine the ARL of light bulbs are conducted under conditions that more or less simulate the environment at your business premises. This means that if the light bulbs at your commercial premises are installed in a heated environment, like in a space that houses a furnace, or in a cold place, like inside a freezer or remain exposed to the elements during winter, it is likely that some of them will burn out within a much shorter time than is indicated by their ARL values.
Similarly, a lighting device that is installed in a humid area of your business space, like near a sprinkler, or one that is near some piece of vibrating machinery may have a much shorter lifespan than a similar one with the same ARL but is installed in a less stressful area.
ARL tests on fluorescent bulbs are carried out in the following sequenced manner: the lights are switched on and kept burning at a stretch for three hours and then switched off for 15 minutes. This sequence is repeated until half the bulbs (50 percent) in the test batch burn out. This is the standard procedure for determining the ARL of T8, T5 and T12 lights.
The conditions for ARL tests vary depending on the nature of the lamp. For instance, in case of high-intensity discharge (HID) lamps, like high-pressure sodium and 400W metal halide lights, the bulbs being tested are kept on for 10 hours per start.
T5 bulbs are increasingly being used in commercial spaces. The ARL value for these bulbs is calculated by keeping these lights switched on for three or 12 hours per start and determining the time within which 30 percent of the bulbs being tested die out.
What Affects the Longevity of Light Bulbs and Lamps?
While the ARL value of a light bulb reflects the average lifespan of the device, you can also undertake the following measures to ensure that your lighting apparatus runs for as long as possible:
- Do not switch light bulbs and switch them off frequently. The longevity of a lighting device is affected considerably by the number of lamp starts. The lifespan of a light bulb increases when the number of burning hours per lamp start increases. The following graph illustrates the effect of the duration of operation of a lamp to its longevity.
- Install your light bulbs in favorable operating conditions. However, there will be certain areas at your place of business where the environmental conditions will not be conducive to the optimal functioning of a lighting apparatus. You have to strike a balance between selecting a lamp with longer a lifespan that costs more and settling for a lighting device that optimizes your investment.
- Use the ballast recommended by the manufacturer for the light bulbs installed on your commercial property. The ARL value of many lamps is based on operating the lighting devices using rapid-start ballasts.
Knowing what to make out from the ARL rating of a particular lighting device will help you make the right choice for your business.
What is the Average Rated Life of Different Lamp Technologies?
There are many different technologies in lighting that easily go back 100+ years back to the first filament based incandescent bulbs. It is amazing that the old technologies are still used today, but they are also starting to be phased out and replaced with much more energy efficient and longer lasting technologies.
In general, the newer the technology, the longer the light source will last. The exception to this would be induction lamps, which goes back 50+ years and lasts 100,000+ hours. Most of the commercial and industrial lighting products installed today include fluorescent, induction, and LED. LED is on the rise and will soon be the dominant technology in almost all lighting applications.
Here is a chart of the different technologies through the years and their average rated life:
Some Real World Examples of Average Rated Life.
Example 1: Large industrial manufacturing facility.
This could be a 50,000 to 100,000+ square foot area that may manufacture gym equipment or is an automobile plant with tons of moving parts and automated equipment. The area must not only be well lit but should contain technology that lasts a long time. Without going into detailed Payback and ROI calculations (that is another topic), imagine what it costs to shut down an assembly line for even a few hours to change out the light bulbs! This not only means either renting or operating lifts to get you up to 20+ feet in the air, but includes the hourly labor, product cost (new lamps), and the opportunity cost, or revenue lost, from shutting down all the equipment.
In this case, it makes sense to not only install energy efficient equipment to bring down the electricity costs, but spend a little bit more to have the longest lasting technology possible, which in today's market would include LED or induction. The plant may have quantity 250 metal halide high bay fixtures that only last 12,000 hours for instance, and a good retrofit would be a new 70,000+ hour LED high bay light fixture, which is almost six times longer lasting. Along with the payback from the energy savings itself, the decreased maintenance cost and savings from not shutting down assembly lines so much recoups the money spent on the project pretty quickly indeed.
Example 2: Car Dealership
Car dealerships have one goal - to sell cars. And most of these cars are in the lot outside, with a lot of people coming in at night after work to look at them. Very bright and well lit areas are a necessity to show these cars off. You not only need a very bright area, but color quality (see CRI), color temperature, and the cost of maintenance all matter. Up until recently, this also meant a massive electric bill due to the lighting cost and wattage needed to have a very bright parking lot given the available technology.
Given that most dealerships still have metal halide light bulb that last only 12,000 hours (about two years at 12 hours per day average), an equally big issue is the light depreciation. Metal halide technology has a rapid light output depreciation shortly after they start to burn. This means that about six months after new HID bulbs have been installed, they already start to lose their light output and look dim. This then decreases the appeal of the car or dealership and sales are lost. To counteract this a lighting maintenance plan is often put in place to change out the bulbs every year or less. This means labor, bucket trucks, trip charges, buying tons of bulbs, and overall means a huge expense just to keep the place bright.
A switch to new technology eliminates this problem while keeping the area bright as well. The above picture is the Honda dealership of Greeley, CO, where we supplied 200W induction retrofit lamps to replace the old 400W metal halide light lamps and ballasts. The result is an increase from 12,000 hours (maximum) to a 100,000 hour induction technology. On top of that, induction has a much slower light loss depreciation curve - so after 10 years of operation, induction still puts out 75-80% of it's initial light output. 56% energy savings was also achieved because induction puts out brighter light for the wattage used. LED is also a great option for car dealerships, and many are rapidly switching over to the new technology due to all the benefits.
In general, it's always best to get the longest-lasting bulb technology you can find. Cost, however, almost always plays into the decision and can be prohibitive. It is best to analyze your area that needs lighting and think about what it costs or to what degree of difficulty it takes to replace the bulbs. If it's very expensive or difficult, most of the time it makes sense to spend more to get longer lasting, commercial grade bulbs. This would currently include LED or induction. If your area is easy to get to and cost is a factory, go for T8 or T5 fluroescent, or CFL for the smaller bulbs. They are plenty energy efficient and the cost is very good on these now.