Summary of Proposed Test Procedures for White LED Products*
Goal: To conduct field research and demonstrations involving off-grid LED systems.
- Mills, E. and A. Jacobson. 2008. "The Need for Independent Quality and Performance Testing of Emerging Off-Grid White-Led Illumination Systems for Developing Countries." [PDF]
| # | Test Procedure | Metric | Notes |
|---|---|---|---|
| Illumination Sub-System | |||
| 1 | Luminous Flux | Lumens | Total lumen output for system (captures effects of power supply ("driver"), optics, and light source). Measurement of total luminous flux is made with an integrating sphere. Use of goniometer allows also for characterization of light-distribution pattern. |
| 2 | Light Source Luminous Efficacy |
Lumens/watt | Ratio of the results of Test 1 to power delivered to light source, independent of the device and optics in which the LED is mounted. |
| 3 | Luminaire Efficiency Luminaire Efficacy |
% lumens/watt |
Ratio of luminous flux from Test 1 to sum of light emitted from LEDs in test 2; Ratio of luminous flux from Test 1 to power input. |
| 4 | Light Distribution Uniformity | Array of lux measurements in in three dimensions | Measurement of the production, extraction, and distribution of light output of entire system (source + optics). Measurements of the light source using a goniometer as well as the illumination incident on a task surface are both useful. Relatively uniform distributions are preferable for reading and task lighting applications. See Figures 7-9. |
| 5 | Light output over a single discharge cycle | Lux as a function of time; Discharge cycle | Measurement of the light output, voltage and current draw of the lamp during discharge of battery.. See Figure 13 for an example. |
| 6 | Long-Term Light Output |
Lux as a function of time; Lamp Life |
Measurement of lamp lumen depreciation over time. High-quality LEDs can maintain high lighting levels for tens of thousands of hours, while the output of lower quality products declines much more rapidly. These longer-term measurements can require 12+ months. |
| 7 | Color | Correlated Color Temperature; Color Rendering Index; Color Quality Scale | Measurement of the color-quality of the light sources. See Figure 5 for an example. |
| 8 | Glare | Luminance | Measurement of the intensity of light from the source itself. This is important given the small size of LED lights and their corresponding brightness, which can cause discomfort glare as well as injury if users look directly into the light. |
| Energy Storage Sub-System | |||
| 9 | Storage Battery Capacity |
Ampere-hours | Primary measurement of battery size (in ampere-hours). The measurement is made by discharging the (new) battery fully at a constant current. The result is compared to the advertised battery capacity. See Figure11 for an example. |
| 10 | Battery Cycle Life | Persistence of battery capacity | Primary measurement of battery performance over time. Each battery is charged and discharged at rates that approximate actual operating conditions until the battery storage capacity drops to 50% of its original capacity. These measurements are critical for evaluating the longevity and life cycle cost of off-grid WLED products. Measurements can last 2-12 months or more per battery, and equipment limitations can restrict the number of batteries that may be tested at one time. |
| 11 | Storage Battery Charging |
Performance of charging system | Measurement of voltage, temperature, and current input to the battery during charging. This test provides information about the electronic circuit used to regulate charging in the WLED device, as well as the potential for damage to the battery due to over-charging or high temperature. The test can be carried out multiple times with different charging sources as applicable (i.e. charging with grid and/or solar). Outside air temperature should be measured at the same time. |
| Charging Sub-System | |||
| 12 | Solar PV Module Performance | PV module power output (Watts) | Measurement of the power output of the solar module for standard test conditions. This is the primary performance indicator of a solar PV module. The performance of crystalline silicon modules can be evaluated with a single test, while the performance of amorphous silicon (thin film) modules must be evaluated over 4-6 months to account for light induced degradation. See Figure 14 for an example. |
| 13 | Charging and Battery Storage System Efficiency | % | Ratio of energy input to the charging system (e.g. from a solar PV module or an AC power source) over a charging cycle to the energy delivered to the lamp over a full charge and discharge cycle. This result draws information from tests #5 and #11. |
| Integrated Performance | |||
| 14 | Application Efficiency | Services/Watt (e.g. Lux-area/Watt) |
Ratio of total useful light delivered to the energy input. |
* Note: Certain tests may usefully be replicated using a standardized battery with known properties. This would be useful in helping isolate the contributors to performance outcomes.
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