Parameters and Characteristics of Light-Emitting Diodes

Release Date:

2020-12-09

　　1. Light-emitting diode power supply

　　Typical LED bulbs have a power rating of less than 12 W. Standard LED bulb wattages include 3 W, 4 W, 5 W, 6 W, 7 W, 8 W, 9 W, and 10 W.

 

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　　2. Light-emitting diode Voltage and Current

　　Voltage and current are also critical fundamental parameters for LED bulbs. Grid voltages vary from country to country, and in some applications specific voltage levels are used. Commonly employed voltages include 12 V, 110 V, 220 V, and 85–265 V. Current is categorized into input current and LED chip current. First, input current: this can be measured using a power supply; values differ depending on the wattage, so instrument readings should be taken as the reference. Second, LED chip current: typically, high-power LEDs operate within the range of 300 mA to 320 mA. Current has a significant impact on the light output degradation of LED lamps, making current stability crucial. The current and voltage supplied to the LED chips must not exceed safe limits, as excessive values can severely shorten the lamp’s service life.

　　3. Light-emitting diode lighting effects

　　Luminous efficacy is also a key factor for LED bulbs. Currently, the domestic luminous efficacy of Taiwan-made LED chips generally ranges from 100 to 130 lm/W.

　　4. Luminous Flux of Light-Emitting Diodes

　　Luminous flux is primarily determined by the luminous efficacy and power of the LED bulb. It is typically measured using an integrating sphere.

　　5. Illuminance of Light-Emitting Diodes

　　Illuminance is something lighting designers typically consider quite extensively, whereas in most other contexts we tend to give it less attention. The unit of illuminance is the lux, defined as the illuminance produced when a luminous flux of 1 lumen is uniformly distributed over a surface area of 1 square meter. Illuminance is usually measured with an illuminance meter, which is simple to use and relatively inexpensive. In the absence of an integrating-sphere system, an illuminance meter can be used for preliminary measurements as a rough reference.

　　6. Light Degradation of LEDs

　　Simply put, light depreciation refers to the degree to which a bulb’s brightness decreases after it has been in use for a certain period. The primary factors affecting LED light depreciation are heat dissipation and current. Unstable current and poor heat dissipation can lead to severe light depreciation. However, if an LED bulb is equipped with an isolated constant-voltage/constant-current LED driver and a heat-sink aluminum lamp housing, light depreciation can be kept below 0.2%.

　　7. Color difference of light-emitting diodes

　　Color difference refers to inconsistencies in color temperature; it is particularly relevant for warm white light (2700–3200 K). Warm white light is what we commonly call “yellow light.” Sometimes, when you purchase two energy-saving lamps of the same brand and wattage that both emit yellow light and illuminate them under the same lighting conditions, you may notice that one appears brighter while the other appears dimmer—this is color difference. In certain applications, color difference is unacceptable.

　　8. Light-emitting diode Color rendering

　　The degree to which a light source renders the true color of an object is known as color rendering, or color fidelity; the color-rendering index (CRI) quantifies this property, indicating how closely the colors of objects under a given light source match those under a reference light—typically daylight. Color deviation fully reflects the color characteristics of a light source. Light sources with high color rendering deliver superior color reproduction, resulting in hues that appear close to natural. In contrast, sources with low color rendering exhibit poorer color performance and produce more pronounced color deviations. The International Commission on Illumination (CIE) assigns a CRI of 100 to sunlight. Different light sources have varying CRIs: for example, high-pressure sodium lamps have a CRI of Ra = 23, while fluorescent tubes range from Ra = 60 to 90. There are two main types of color rendering: faithful color rendering, which requires a light source with a high CRI (Ra) to accurately reproduce the original colors of materials, ideally approaching a value of 100 for optimal color fidelity; and accentuated color rendering, which uses color enhancement techniques to highlight specific hues and create a more vivid, aesthetically pleasing visual experience.

　　9. LED Glare

　　Objects with extremely high luminance or strong luminance contrast in the field of view can cause visual discomfort known as glare. Glare is a significant factor that affects lighting quality.

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