Light Loss Factors, L70 Ratings, and IES Standards
Light loss factor is a key metric that must be considered when determining the luminaires required to meet IES standards for a particular installation. Part of knowing what to use for a light loss factor is based on the L70 of the luminaire and the hours per day, and thus per year, that the area will be illuminated. Let's dive into what these terms mean, why you want to get this right, and how to determine the correct light loss factor for effective illumination.
LED Lumens vs. Luminaire Lumens
Every LED light fixture has two key performance factors based on light emission: the LED lumens and the luminaire lumens. LED lumens are the total lumens that the LEDs emit. Luminaire lumens, also known as design lumens, are the lumens emitted from the LED light fixture. The reason there is a difference is that while the LEDs emit x lumens, those lumens still need to exit the luminaire through optics and possibly a lens. For example, a prismatic glass lens will reduce the lumen output of the LEDs by 20%. What matters is not the lumens the LEDs can emit. What matters is the actual lumens the luminaire can emit. It is luminaire lumens that matters.
Every figure Access Fixtures publishes is a delivered luminaire lumen. The STAD 850 is listed at 143,627 delivered lumens and 171 lm/W. That is what leaves the fixture, not what the diodes make inside it.
What an L70 Rating Actually Tells You
All LED luminaires have an L70 rating that states the lumen maintenance. This is listed as an L70 rating, such as L70 at 50,000 hours or L70 at 200,000 hours. An L70 lumen maintenance rating lists the point at which the lumens are 70% of the initial lumen output of the LEDs. L70 at 50,000 hours means that after 50,000 hours the LEDs will emit 70% of the initial lumen output. If an LED luminaire has an initial light output of 80,000 lumens and is rated L70 @ 50,000 hours, then at 50,000 hours of use it will emit 70% of 80,000 lumens, which is 56,000 lumens.
Read that definition carefully, because it is the single most misunderstood number in sports lighting. The rated hours are the point at which 30% of the light is gone. They are not a percentage of anything else, and a fixture that is down to 70% output at some earlier hour mark is, by definition, rated at that earlier hour mark instead.
Unlike legacy lighting sources like metal halide, LED lumen depreciation is treated as linear for design purposes. As such, if you have the L70 rating, you can calculate the lumen depreciation based on the amount of time the light fixture has been in service, or, looking into the future, will be used.
Lumen Output After X Hours = Initial Lumens − ((Hours of Use / L70 Rating Hours) × (0.3 × Initial Lumens))
Example, 80,000 initial lumens, L70 @ 200,000 hours, at 50,000 hours: 80,000 − ((50,000 / 200,000) × (0.3 × 80,000)) = 74,000 lumens
Where an L70 rating comes from
An L70 rating is a projection, not a measurement of a fixture somebody ran for 200,000 hours. LED lumen maintenance is measured under IES LM-80 and projected forward under IES TM-21. Access Fixtures states ASTA rated life as L70B10 above 200,000 hours and L90B10 above 60,000 hours, projected from IES LM-80-23 data. The B10 designation matters: it means the projection applies to at least 90% of the population.
The linear depreciation model used throughout this page is the practical specification convention. The exponential decay curve that TM-21 actually applies runs marginally steeper. Across the service windows in the examples below the difference is under two percentage points, which is why the linear model remains a sound basis for specification.
The Standards Publish Maintained Values, Not Initial Values
This is where light loss factor stops being academic. ANSI/IES RP-6-22 publishes recommended maintained illuminance targets, not initial ones. A design that hits the target on opening night and nowhere else has not met the standard.
For baseball, the recommended maintained horizontal illuminance is as follows (per ANSI/IES RP-6-22, Table A-2, measured at 0.91 m / 3 ft above grade):
| Class of play | Infield | Outfield | Max:Min uniformity, infield |
|---|---|---|---|
| Class I | 150 fc | 100 fc | 1.3:1 |
| Class II | 100 fc | 75 fc | 1.5:1 |
| Class III | 50 fc | 30 fc | 2:1 |
| Class IV | 30 fc | 20 fc | 2.5:1 |
Class is set by spectator capacity (per ANSI/IES RP-6-22): Class I is a facility with capacity over 5,000, Class II is up to 5,000, Class III is up to 2,000, and Class IV has limited or no provision for spectators.
RP-6-22 is explicit about the designer's obligation here. Annex E states that it is good practice to calculate both initial and maintained light levels, and that the maintained calculation should identify the light loss factor clearly so the expected performance of the system over time can be evaluated. A photometric study without a stated light loss factor is an incomplete photometric study.
Know Which Standard Governs Before You Calculate Anything
Two governing bodies can specify the same field and land on different numbers. A college baseball field with 3,000 seats is IES Class II, which sets 100 footcandles maintained on the infield. The NCAA's own best-practice sheet for the same field specifies 70 footcandles on the infield and 50 on the outfield, with 2.0:1 infield uniformity on a 30 ft x 30 ft grid (per NCAA Best Lighting Practices: Baseball, Standard Intercollegiate Play, L-1703-2).
That is a 30 footcandle spread on the infield, and it changes the fixture count. Confirm which document the project is being held to before modeling anything, and confirm it in writing.
One further caution on the NCAA sheets: they state a footcandle level without specifying whether it is initial or maintained. RP-6-22 says maintained explicitly. When a specification is silent on that distinction, treat the number as maintained and state that assumption in the photometric submittal.
The Maintenance Factor on Your Drawing Is a Light Loss Factor
Every Access Fixtures photometric study carries a maintenance factor. Most published court and field layouts use 0.90, which is a 10% light loss factor. That single number means something completely different depending on which fixture is under it.
A 10% light loss factor arrives at 16,667 hours on a fixture rated L70 at 50,000 hours. It arrives at 66,667 hours on a fixture rated L70 at 200,000 hours. Same maintenance factor on the drawing, four times the service life underneath it.
Translate that into a calendar and the specification decision makes itself.
| Facility schedule | Hours per year | STAD holds the standard | ASTA holds the standard |
|---|---|---|---|
| Club, 49 hours a week, year round | 2,548 | 6.5 years | 26 years |
| School, 30 hours a week, 30 weeks | 900 | 19 years | 74 years |
| Recreational, 10 hours a week, 26 weeks | 260 | 64 years | 256 years |
Read the top row and the bottom row together, because they are the whole argument. A busy club that runs lights seven nights a week gets six and a half years out of a 0.90 maintenance factor on a STAD. A seasonal recreational court gets sixty-four. Neither fixture is the right answer for both facilities, and specifying an ASTA on the bottom row sells a customer service life they will never use.
What Metal Halide Taught the Industry
Sports fields were illuminated with metal halide lighting. A 1,500 watt metal halide lamp could suffer 30% lumen depreciation in 1,500 hours, while a 1,000 watt pulse start metal halide lamp would reach 30% lumen depreciation over 15,000 hours. Because the depreciation was that severe and that fast, systems were designed well above the target level, and group cleaning and re-lamping were scheduled for the point at which lumen depreciation reached roughly 30%.
How does this reflect on LED lighting? Access Fixtures' STAD is rated L70 at 50,000 hours, and EXTREME-LIFE sports fixtures such as the ASTA are rated L70B10 above 200,000 hours. Lumen depreciation still has to be taken into consideration, but the cushion between initial footcandles and maintained footcandles can be far smaller than metal halide required. That raises three questions.
Do we have to design the initial footcandles 40% above the maintained target the way metal halide forced us to?
If we have a STAD rated L70 at 50,000 hours and an ASTA rated above 200,000 hours, should the light loss factor be the same for both?
What should the initial footcandles be, and how do we determine that?
Example One: A Class I Baseball Field, Ten Years
A professional baseball team wants a lighting system that will meet their lighting requirements for ten years. The team plays 81 games per season at their home field. With set up and cleanup each game runs 8 hours, for 648 hours per year of use. That number is almost certainly too low, because the lights are turned on a lot more than that. There are events, tours, grounds maintenance, and whatnot. Assuming the lights are on for an average of 8 hours per day, 365 days a year, the hours of use would be 2,920 hours per year. Over ten years that is 29,200 hours.
The facility seats more than 5,000, so it is Class I, and the maintained infield target is 150 footcandles (per ANSI/IES RP-6-22, Table A-2, Class I — 150 fc maintained infield). The light fixture for this example is the ASTA. How many initial footcandles do we need, and what is the light loss factor?
Work the equation in footcandles, because footcandles are what the standard governs.
Light Loss Factor = (Hours of Use / L70 Rating Hours) × 0.3
= (29,200 / 200,000) × 0.3 = 0.044, or 4.4% light loss
Initial Footcandles Required = Maintained Target / (1 − Light Loss Factor)
= 150 / 0.956 = 156.9 initial footcandles
Design the ASTA system to 157 initial footcandles and it still delivers 150 maintained footcandles after ten years of running eight hours a day, every day. The light loss factor is 4.4%. That is the entire cushion the system needs, and it is less than half the 0.90 maintenance factor most layouts already carry.
Example Two: The Same Field With a STAD
Now run the identical project on the STAD, rated L70 at 50,000 hours. Same field, same 150 footcandle maintained target, same 29,200 hours.
Light Loss Factor = (29,200 / 50,000) × 0.3 = 0.175, or 17.5% light loss
Initial Footcandles Required = 150 / 0.825 = 181.9 initial footcandles
The ASTA needs 157 initial footcandles. The STAD needs 182. That is 25 additional initial footcandles to deliver the identical 150 maintained footcandles in year ten. Sixteen percent more initial footcandles requires roughly 16% more delivered lumens, which at equal efficacy requires roughly 16% more connected wattage.
Note also that a 17.5% light loss factor is larger than the 0.90 maintenance factor on most published layouts. A STAD design for this schedule cannot use the standard 0.90 assumption. It has to be modeled at 0.825.
Same field. Same standard. Same experience for the player on opening night. A different fixture count, and a different number on the electric bill every month for ten years.
What a Light Loss Factor Costs
Here is where the light loss factor stops being an abstraction and becomes a purchase order.
Assume the smaller STAD delivers the exact footcandle level the project requires on day one, with a light loss factor of zero. We know depreciation is coming. So can the project use that smaller STAD? No. It has to move up, and cost goes up with it.
How far up depends entirely on how many rungs the ladder has.
The STAD line has three models. The 570 delivers 88,238 lumens, the 650 delivers 100,120, and the 850 delivers 143,627. The first step up is 13.5% more light. The second is 43.5%. From the smallest to the largest is a range of 1.6 to 1. A project that needs 20% more light than the 570 delivers has to buy the 650 and gets 13.5%, or buy the 850 and pay for 63%.
The ASTA line has eighteen models, from 40W at 6,080 lumens to 1,440W at 184,320 lumens. That is a range of 30 to 1, with a median step of roughly 22% between adjacent models.
Neither ladder is infinitely fine. In the high-output range that large fields need, both step coarsely. Real precision comes from three levers together: the model, the fixture count per pole, and dimming. Every STAD and every ASTA dims continuously, so a design can be built with headroom for depreciation and run at a reduced level until it is needed. That is the least expensive way to carry a light loss factor, because it costs commissioning time rather than fixtures.
The chain runs in one direction and every link is fixed. The light loss factor sets the required initial footcandles. The required initial footcandles set the delivered lumens. The delivered lumens set the model and the count. The model and the count set the cost. Calculate the light loss factor correctly and the project buys exactly the lighting system it needs.
Turning a Light Loss Factor Into Hours
A light loss factor is a percentage. A facility manager thinks in seasons and years. This table converts between them for both L70 ratings.
| Light loss factor | Maintenance factor | Design initial above target | STAD hours at standard | ASTA hours at standard |
|---|---|---|---|---|
| 5% | 0.95 | 5.3% | 8,333 | 33,333 |
| 10% | 0.90 | 11.1% | 16,667 | 66,667 |
| 15% | 0.85 | 17.6% | 25,000 | 100,000 |
| 20% | 0.80 | 25.0% | 33,333 | 133,333 |
| 30% | 0.70 | 42.9% | 50,000 | 200,000 |
Read the table this way: a STAD designed with a 20% light loss factor holds the maintained IES target for 33,333 hours of use, and its initial design has to sit 25% above that target. An ASTA designed with the same 20% light loss factor holds the standard for 133,333 hours. Four times the L70 rating delivers four times the hours at every light loss factor on the table.
Notice the bottom row. A 30% light loss factor is the metal halide design convention, and it demands an initial design 43% above the maintained target. That is the cost of a short L70 rating, expressed in footcandles.
Good, Better, Best on One Project
Two fixture families and one table produce three legitimate solutions for the same field. Every one of them meets the maintained IES target. They differ in how long they hold it.
Good — STAD at a 10% light loss factor. Design initial footcandles 11% above the maintained target. The system holds the standard for 16,667 hours of use. This is the standard 0.90 maintenance factor, and on a seasonal facility it is decades of service.
Better — STAD at a 20% light loss factor. Design initial footcandles 25% above the maintained target. The system holds the standard for 33,333 hours, and pays for it in wattage.
Best — ASTA at a 10% light loss factor. Design initial footcandles 11% above the maintained target. The system holds the standard for 66,667 hours, and carries a ten-year warranty rather than five.
Three price points. Three service lives. One standard met in all three cases. That is a real good, better, best conversation, and it is built on arithmetic rather than adjectives.
Two Facilities, Same Math, Different Answers
A seasonal community court used 10 hours per week, 26 weeks a year. That is 260 hours a year. A STAD designed with a 10% light loss factor covers 16,667 hours, which is 64 years of that schedule — longer than the poles. Is a STAD at the standard 0.90 maintenance factor more than sufficient for that facility? Decisively yes.
A southern club pickleball complex, lights on at 6:00 p.m. and off at 1:00 a.m., seven nights a week, year round. That is 7 hours a night, 49 hours a week, 2,548 hours a year. Over 20 years the system accumulates 50,960 hours. The maintained target for club play is 50 footcandles (per ANSI/IES RP-6-22, Section 5.19, Class III — 50 fc maintained, equivalent to USPA Class II: Club).
A STAD passes its full L70 point inside that 20 year window, so it cannot hold the standard for the life the customer is asking for. An ASTA at 50,960 hours shows 7.6% light loss and needs 54.1 initial footcandles to still deliver 50 maintained footcandles in year 20.
Same math. Same table. Two facilities that require different fixtures, and the answer falls out of three inputs: hours per night, nights per week, and required years of service.
Light Loss Factor Is More Than Lumen Depreciation
Lumen depreciation is the largest and most predictable component of light loss, and it is the one an L70 rating quantifies. It is not the only one. ANSI/IES RP-6-22 Annex E.7 states that the total light loss factor comprises mainly light source lumen depreciation (LLD), luminaire dirt depreciation (LDD), ambient temperature factor (ATF), and ballast factor (BF).
Two of those deserve attention on outdoor sports projects. Luminaire dirt depreciation matters wherever airborne dust, pollen, or salt accumulates on the lens between cleanings. Ambient temperature matters because, as RP-6-22 puts it plainly, the effect of ambient temperature on the output of LED luminaires is considerable, and the designer is expected to obtain output data at the actual operating temperatures. Both the STAD and the ASTA hold output to 50°C ambient, which keeps the temperature factor small on hot-climate projects.
RP-6-22 also identifies two factors that affect the initial light level rather than the maintained one: the field factor and the lamp tilt factor. An Access Fixtures lighting engineer assigns all of these per project rather than applying a single house number to every job.
One Alternative Worth Knowing About
RP-6-22 describes lumen maintenance control systems, which adjust light output over time rather than over-designing the initial level. Luminaires are operated initially at reduced wattage, and current is increased as the source ages and dirt accumulates, holding output more consistent across the life of the system.
Every STAD and every ASTA dims continuously, so the hardware for this is already in the fixture. For a facility that runs enough hours to need a large light loss factor, running the array at a reduced level for the first years and stepping it up later can cut energy consumption meaningfully compared with running at full initial output for twenty years. It adds commissioning discipline rather than hardware cost. Whether it pencils depends on hours of use and local energy rates.
Three Questions That Set the Light Loss Factor
A lighting engineer needs three inputs to calculate a defensible light loss factor and the initial footcandles that follow from it.
- Which document governs, and what is the maintained target? ANSI/IES RP-6-22 and the relevant governing body can specify different levels for the same field. The standard drives every number downstream.
- How many hours per week, and how many weeks per year? Usage is what converts an L70 rating into a calendar.
- How many years must the system hold that standard? This is a business decision, and the customer owns it.
Answer those three and the light loss factor is arithmetic. Skip them and the design is a guess.
Run Your Own Numbers
Light Loss Factor Calculator
ANSI/IES RP-6-22 publishes maintained illuminance targets. Enter the maintained target and the projected use, and this returns the light loss factor, the initial footcandles a design has to deliver on day one, and whether the standard 0.90 maintenance factor covers the schedule.
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Access Fixtures Solutions for Sports Lighting Life-Cycle Specification
STAD LED Sports Lights
Three models — 570, 650, and 850 — rated L70 at 50,000 hours with a five-year warranty. The right choice for seasonal and recreational schedules where a 0.90 maintenance factor already holds the standard for decades.
Shop STAD Sports Lights →ASTA EXTREME-LIFE Sports Lights
Eighteen models rated L70B10 above 200,000 hours with a ten-year warranty. The right choice for high-use club, professional, and year-round facilities where the light loss factor has to hold for decades under heavy hours.
Shop ASTA Sports Lights →Sports Lighting Photometric Studies
Send the field dimensions, the governing standard and class of play, projected hours of use per week, and the years the system must hold the standard. An Access Fixtures lighting engineer assigns the light loss factor and returns a photometric plan for day one and year twenty.
Request a Photometric Study →Get the Photometric Study
Access Fixtures provides photometric studies for sports, area, and security lighting projects. Send the field dimensions, the governing standard and class of play, the projected hours of use per week, and the number of years the system must hold the standard. An Access Fixtures lighting engineer will assign the light loss factor, model the initial footcandles, and return a photometric plan showing what the facility delivers on day one and in year twenty.
Sources: ANSI/IES RP-6-22, Recommended Practice: Lighting Sports and Recreational Areas — Table A-2, Section 5.19, Annex E, Annex E.7. NCAA Best Lighting Practices: Baseball, Standard Intercollegiate Play (L-1703-2). IES LM-80-23 and IES TM-21 for LED lumen maintenance measurement and projection. Fixture figures per the STAD Sports Category Guide v260821 (STAD Master Fact & Consistency Sheet v260819-r5) and the ASTA LED Sports Lights guide v2608.