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What is it, and why do we need it? L70
In the lighting industry, the word “L70” is a stamdard term about LED lifespan. Do you understand what it actually implies? Do you know why it’s significant? Let’s go over the fundamentals of L70.
When an LED reaches L70, it means that it has produced 70% of its initial light output. For instance, an LED light fixture that initially delivers 10,000 lumens will eventually dim to 7,000 lumens. L70 is the designation of this instant in time. The difference in the time it takes for an LED light to reach L70 is critical for a buyer to understand in order to make an informed long-term purchase because all LED light sources degrade.
Academics and industry experts from the lighting industry make up the nonprofit Illuminating Engineering Society. The lighting industry had encountered a comparable problem with a prior lighting technology, Mercury Vapor, therefore the necessity for L70 was well understood.
In the 1960s through the 1980s, mercury vapor lamps were widely utilized in commercial and industrial settings and were renowned for their long lifespan. The issue was that, despite only producing a very small portion of their initial light output, they gave off the impression that they were illuminating.
The maintenance staff was hesitant to change a light bulb that was “functioning.” This practice of leaving lights on even when they weren’t producing much light but were still using the same amount of energy resulted in significant safety risks as well as decreased productivity.
The IES aimed to offer recommendations for when to replace an LED lamp once LED technology was commercially feasible as a source of general lighting. It was discovered after lengthy research that a change in light brightness could not be accurately sensed by humans until it reached 30%. Therefore, it was established that the ideal time to replace an LED light source is when its original light output has decreased by 70%.
A light level below 70% of the original design is deemed unsatisfactory and may result in liability for the space owner if the lighting designer of the space applies the IES suggested minimum light level for a certain task.
Why do some LED lights achieve L70 more quickly than others?
How long does it take a lighting fixture to reach L70? It depends on a number of things, but there are two main factors: the quality of the components and the fixture’s ability to dissipate heat.
Has your fixture been constructed with high-quality materials?
Low-quality components are the main reason why LED fixtures lose their light output more quickly than others. In order to meet the cost targets, manufacturers of LED fixtures must make decisions – and compromises – about the caliber of materials and components to be employed for the end product.
The majority of LED fixtures produced for commercial use go through a bid process, with the lowest bidder getting the job. This forces the majority of producers to make compromises and pick the cheapest materials and components they can without the customer seeing or objecting.
Can your fixture dissipate heat efficiently?
Heat is the second important component affecting lumen depreciation or loss of light production. Electronics do not enjoy heat, as the majority of people have discovered when leaving their phones in the sun. Heat rises quickly in unconditioned environments, right where the light fixtures are placed. The use of better-grade components and materials with higher thermal conductivity is required to keep the electronic components cool inside LED fixtures that are exposed to high heat, which raises the cost of materials.
Aluminum is the most economical material to use when creating LED lighting that can endure the intense heat found in most industrial environments. Because sheet metal is less expensive than aluminum but not nearly as effective at dissipating heat, it is the material of choice for producers looking to win low bid procedures.
The temperature at the light fixture will typically be 1 degree hotter for every foot above the floor if the temperature on a manufacturing floor is 80 degrees Fahrenheit. The end user may find it challenging to determine the lumen output of their LED fixture during the warmest time of the year because the majority of LED light fixtures are only tested at 77°F (25°C). Will it be sufficient to achieve the suggested light levels for worker security and efficiency? What would occur in years five and beyond if that were unknown from day one?
The engineering behind LED lighting fixtures is also crucial. A key component is heat sinks made of vertical fins that are parallel to LED boards. The manner of attachment is equally critical because heat sinks must be attached to the LED boards in order to function. Screws are the least expensive method of fastening LED boards. Although this approach is inexpensive and straightforward for the producer, it ultimately hurts the owner. The LED boards will gradually deteriorate and start to sag in between the screws, removing them from the heat sink. If it can’t keep in touch with the LED board, even the best-designed vertical heat sink constructed of the best metal will be worthless.
An LED light fixture’s design must also consider airflow. The fixture will operate substantially cooler if the design enables air to flow from underneath it and pass through it, rather than just around it.
The greatest recommendation for buying LED light fixtures that can withstand industrial conditions is to purchase ones rated for the highest ambient temperature, not just the temperature you believe your facility will ever reach. This is in addition to checking for quality materials and good design specifications.
Are we able to correctly predict L70?
An accurate prediction of L70 is not achievable. Although the exact length of time is uncertain, LEDs will outlast conventional lights. Manufacturers will make predictions about L70, but you can’t rely on them.
Even worse, we don’t completely understand the variance. Although no one is certain of the exact duration, the good news is that LEDs will endure longer than conventional light sources.
The fact that the industry norm for projecting the degradation of LEDs past their “tested” lifetime ignores aging variables in the rest of the system, such as lens and reflector losses over time, makes this more challenging.
Based on test results from a given period of time (often 6,000 to 10,000 hours), L70 predictions are made by multiplying the outcome by 6. Why 6? I’ve been unable to locate that. This is undoubtedly included in a DOE study, but like all the other approaches, it is likely out of date. LED technology advances too quickly.
It is not possible to test the fixture for the entire predicted lifespan since the test results would be obsolete before the test was even finished.
I have developed a great deal of respect for engineers as a result of my 10 years in the lighting industry. Engineers are able to achieve product criteria while steadily bringing down costs. How much effort and money will be spent making sure the LED continues to produce the same light output for longer than 10,000 hours if any LED chip engineer is given a scope of work that calls for the least expensive chip that is efficient enough to be eligible for DLC Premium and provide 10,000 hours of data? I worry that manufacturers of LED chips will create the ideal 10,000-hour semiconductor to deceive these L70 projections.
If this is the case now or in the future, there may be a serious risk to emergency egress light levels. Few site managers are maintaining a 1 foot-candle path of egress, even though most are aware that they should press the button on exit signs once a year to check the batteries are still good. This was not a problem with conventional light sources because routine lamp replacement would raise the light level close to the initial design specifications. This is not the case with LED, as was stated in Part 1 of this blog.
Frankly, this is irrelevant to the majority of people who buy LED lighting. What counts is how much money the buyer will need to set aside to replace the lighting. You must examine the warranty language for LED light fixtures to learn the facts. Most manufacturers only guarantee the percentage of LEDs that are defective; they rarely guarantee how much light an LED will generate over time. The LEDs will continue to use the same amount of energy that they do now as they get older, but they will generate less light per hour. The lumens per watt mentioned on the spec sheet might therefore only be accurate on the first day.
The only way out of this conundrum, in my opinion, is to make it so that someone other than the end user is responsible for paying for additional fixtures and the expense of installing them if the current ones fail to fulfill their obligation to provide a certain level of light. Only then will the manufacturer’s belief match the claims on the spec sheet.
Keep in mind the purpose behind your lighting purchase. need a certain amount of light for a certain period of time. A ten-year warranty does not ensure that there will be enough light for 10 years.
We now need to think about one final issue:
What do we do with LED lights once they reach L70?
As you may recall from the first three sections of this blog, it is considered undesirable when a light fixture’s output is less than 70% of its initial output. To ensure a secure workplace, the owner will need to replace the light (assuming extra money was not spent to initially light the space to higher than IES recommended levels).
Even though we all anticipate LED lights to survive longer than the conventional light sources they are replacing, the time will come to replace them. When that time arrives, you’ll need to have a disposal strategy in place. Since LED lights are considered to be electronic garbage (e-waste), most authorities will not permit their simple disposal in a landfill.
Ironically, a technology that has been heavily marketed as having positive environmental effects may instead raise more environmental issues. Ironic is the substitution of non-recyclable LED tubes for recyclable fluorescent tubes as a “green solution.” It would be wise for every business with a sustainability program to have a plan in place before the inevitable disposal day arrives.
Unfortunately, the factors used to make LED purchase decisions may be directly at odds with sustainability and environmental objectives. As I’ve previously explained, LED producers use less expensive materials with little to no recycling value in order to produce the least expensive LED lighting possible. In many LED lights, aluminum has been substituted with sheet metal and plastic in an effort to reduce costs. Disposal fees may wind up outpacing the cost savings realized on bid day. A great ROI that excludes disposal costs could turn out to be a negative ROI.
Choose premium LED fixtures that offer guaranteed light levels and are made to delay the inevitable day as long as possible if you want to link your shopping aims with sustainability goals.
