Lifespan of LEDs in practice - The LEDvolution approach LED luminaires have a long but not infinite lifespan (useful life)!

April 2015

All lighting products fail at some point …

For conventional, lamp-based lighting systems (e.g. incandescent, fluorescent and high-intensity discharge systems),

failure most commonly results when a lamp “burns out.” In almost all cases, other system components (e.g. the ballast or

luminaire housing) last longer than the lamp and have lifespans that are not dependent on the lamp.

Lamp-based system = failure when lamp “burns out”

Unlike conventional lighting systems, LED systems are mostly not lamp based but a collection of several integrated

components like LED modules, heat sink, power supply units, housing structures and optical elements. Regardless of the

product type, LED system performance and lifespan (useful life) are typically affected by interactions between these

system components.

LED systems = failure when one component fails

Conclusion: Establishing a rated lifespan (useful life) for a complete LED system is further complicated by the cost and

impracticality of traditional lifespan testing, especially because the continued development and advancement of LED

technology can render results obsolete before testing is finished. Consequently, the typical approach to characterising

lifespan is no longer viable for LED systems.

Lifespan (useful life) of LEDs in practice - The LEDvolution approach

LEDvolution defines the lifespan (useful life) of LED luminaires as follows:

The rated lifespan (useful life) assigned by LEDvolution is a statistical estimate of how long a product is

expected to perform its intended functions under a specific set of environmental, electrical and mechanical

conditions.

light

ON

struc-

ture

L70

beam

angle

CCT

1All intended functions are subject to the luminaire being operated within the

electrical values, operating range and environmental conditions specified in

the product data sheet or installation guide.

LEDvolution luminaires’ intended functions during the

entire lifespan:1

1. The LED luminaire produces light.

2. The LED luminaire provides at minimum 70% of the

initial light flux (L70).

3. The LED luminaire’s CCT must not deviate (colour shift)

more than +/- 10% from the initial value.

4. The beam angle and light distribution must not deviate

more than +/- 10% from the initial values.

5. The product’s structure does not undergo major

alterations.

Terminology:

The terms “lifespan” and “useful life” are commonly used in relation to longevity of

lighting products. The proper technical term, however, is “service life” which is

also stated on LEDvolution’s product data sheets.

The rated lifespan (useful life) of a LED system may, among other factors, be affected by its design,

materials, selection of components (LED chips, PSU, etc.), the manufacturing process and the

environment it’s used in (ambient temperature, humidity, etc.). Importantly, the rated lifespan for a

complete LED system (luminaire) cannot be longer than the lifetime of any of its components.

Power

Supply PCB

Lens

(if used)

Reflectors

(if used)

Diffuser

(If used)

Thermal Management

Heat sink Power

Input

Light

Output

LED Luminaire Reliability Management to determine the rated lifespan

LED Chip

1 2 2 3 5 4 6 7 3

5 000 to 70 000 hours2

20 000 to 75 000 hours2

> 50 000 hours2

> 100 000 hours2

Power Management: This functional unit includes the power supply unit (PSU) / driver which

ensures that proper power is delivered to the LED light engine. The reliability of the power supply

unit and the driver is key to the lifespan (useful life) estimate of the LED luminaire.

Thermal Management: This functional unit ensures that the heat generated by the LED light

engine and power system is appropriately dissipated to maximise the lifespan of the LED package

and power system components.

Optical Management: This functional unit ensures that the light generated by the LED light

engine is properly bundled and directed towards the desired surface. This includes lenses, reflectors

and diffusers.

> 100 000 hours2

infinite if used under the right conditions

> 100 000 hours2

2Estimated lifespan dependent on selected

components, supplier selection, product design

and on the environment used in.

Conclusion: Failure of any of these functional units could lead to failure of the LED luminaire. In reality, the overall lifespan of a LED

luminaire can be statistically determined by knowing the lifespan and failure rate of each of these functional units.

Assembly Integrity: This functional unit ensures that the overall housing design and the entire assembly process provide for sufficient long-term

protection from dust, moisture, vibration and other adverse environmental effects.

Power Management Optical Management

LED Luminaire Assembly Integrity

Optical Management

LED system / LED luminaire

1 2

3 3

5

4

6 7

LEDvolution Design Goals and Reliability Impacts on a LED luminaire’s lifespan (useful life)

Power Management Design Goals: For proper operation, the power supply and related electronics must provide a well-controlled and (from electrical transients)

protected drive current and possibly other control and monitoring features. All components must be designed to properly function for the

anticipated life of the product.

Reliability Impact: Component failures due to improperly designed and executed power management may often result in a catastrophic failure of

the LED luminaire, but they can also cause less obvious effects, such as a reduced light output or flicker. Proper power management includes

protection against failure caused by electrical transients. This protection might be built into the driver or might be a separate subsystem of the

LED luminaire.

Thermal Management Design Goals: A reliable heat-conducting design, be it passive or active, is required to remove heat from the LED package and luminaire. The

design should ensure that the LED package operates below a manufacturer-reported LM-80 measurement temperature to achieve the desired

lumen maintenance of the fixture. Also, the design must ensure that temperatures for other devices (power supply, control circuitry, optical

components, etc.) do not exceed the manufacturers specified limits.

Reliability Impact: Improperly designed and executed thermal management will usually result in accelerated lumen depreciation and potentially

degraded colour quality or colour shift of the LED package(s).

Optical Management Design Goals: Component choices and manufacturing methods should be chosen in a way that the optical materials retain their integrity

throughout the life of the product; it is desirable that such components not be life-determining.

Reliability Impact: Optical component failures may degrade lumen output of the luminaire’s LED package(s) or, because of discolouring, may

also result in a colour shift, but rarely result in a catastrophic failure.

Assembly Integrity Design Goals: Luminaire housing design and materials must be designed to offer sufficient protection for the LEDs depending on the anticipated

environment. Repairable designs should allow for simple field replacement of any failed component without degrading the integrity of the

housing or other components.

Reliability Impact: For outdoor or harsh environment applications, housing failure can lead to catastrophic failure of critical light-producing

components. In other cases, mechanical failure may result from insufficient protection for internal components. Any assembly process bears the

risk of occasional random manufacturing defects which might cause failure anytime during the life of the product but should not seriously affect

wear out till end of lifespan.

LEDvolution ECO Grid Light T3

31W / 3000lm / 4000k

Lifespan (useful life): 50 000h

Lumen Maintenance Factor: L80

Working Temperature (Ta): +10 to +40°C

Example of a lifespan estimation by LEDvolution

Power Management PSU / driver from ELT (Spain): ref. LC 142/600C

Maximum ambient temperature (Ta) = +50°C

Lifespan at max. Ta = 50 000 h

Reliability:

•Failure rate 0,2% per 1 000 hours

•Overload protection

•Protection against no load operation

•Overheat protection

•Input voltage: 198 to 264 V (in Europe input is 230 V)

•Power factor: 0,99 (extremely efficiency)

The max. Ta allowed for our luminaire is +40°C. This allows us to estimate a lifespan for the PSU

of over 50 000 hours.

LED Package LED chip from Nichia (Japan): ref. NF2L757DRT

Maximum ambient temperature during operation (Ta) = +100°C

Lifespan at Ta 25°C = 100 000 h (L70) (tested by Nichia during 1 000 hours = 0% failure rate) and

lifespan at Ta 100°C = 50 000 h (L70) (tested by Nichia during 1 000 hours = 0% failure rate).

Reliability:

•Failure rate < 0,1% per 1 000 hours at Ta > 40°C

•Moisture resistance: 90%

The strict observance of the max. Ta and a power supply as specified by the manufacturer allows us to

estimate a lifespan for the LED package of over 50 000 hours (L80).

Thermal Management Passive cooling system of aluminium (AU4SG) with 3M thermal conductive interface pad:

Aluminium thermal conductivity around 237 W per m2 (for 1 mm thickness) 237 W/m-K.

The entire luminaire body is out of steel and also participates in the thermal dissipation.

Thermal simulation operated during minimum 24 hours of continuous use at max. Ta (+40°C).

The positioning of the PSU inside the luminaire is designed to avoid any overheating caused

by the LED package heat dissipation.

The passive cooling is oversized and able to dissipate 2 times more heat (Watts) than generated

by the LED package, the thermal simulation confirmed the sustainability of the thermal management.

Conclusion: The weakest link of the LEDvolution ECO Grid Light T3 is the PSU with a lifespan of 50 000 hours at 40°C.

-> This component determines the overall lifespan of the entire luminaire.