LEDs have many advantages over conventional lighting including longer life, energy efficiency, durability, improved performance at cold temperatures, directional light emission, instant on at full output, rapid on-off cycling capability without detrimental effects, dimming and control capability, opportunity for color tuning, and minimal non visible radiation (ultraviolet and infrared radiation). However, several important factors should be considered before selecting the appropriate light source. Here we aims to help consumers select the appropriate LED lighting for a particular application.
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BASIC GUIDE TO LED LIGHTING
Choosing the Best Product
There are a number of factors that should be considered before choosing LED lights. Choosing the best option for a specific application will likely include evaluating: Lumen output Color quality and appearance Energy use and luminous efficacy Light distribution and angle of view Rated life vs. operational time Life-cycle cost Dimming characteristics, flicker, and audible noise Compatibility with new or existing luminaires and building systems
Lumen Output
Lumen is the rate at which a source produces light. The light output is the total amount of light emitted by the source in all directions per unit time. Higher lumens correspond to brighter light while lower lumens correspond to dimmer light. The selected LED light should be capable of providing enough light to achieve the proper lighting level required.
Color Quality and Appearance
Objects are not inherently colored, but rather reflect different proportions of radiant energy. Thus, if the light incident on a surface changes, the apparent color of the object may change. Depending on the light source, this shift can be small or large. Color of LED lights is typically characterized using the correlated color temperature (CCT) and color rendering index (CRI) metrics.
Color Rendering Index (CRI)
The color rendering index measures the ability of a light source to render colors, compared to either incandescent reference sources if warm in color, or daylight reference sources if cooler in color. At the maximum CRI value of 100, the colors of objects would be seen as they would appear under an incandescent or daylight spectrum of the same CCT. In general, a minimum CRI of 80 is recommended for interior lighting, with CRIs of 90 or higher indicating excellent color rendering.
The CRI has been found to be inaccurate for RGB (red, green, blue) LED systems because it’s poor at predicting the quality of the appearance of saturated color objects, and doesn’t correspond well to human perception of color quality. Hence, CCT and CRI together give only an approximate figure for selecting and matching lamp colors. A number of new color-rendering metrics have been proposed in recent years, but none have been widely adopted as of yet. In the meantime, color rendering of LED products should be evaluated in person and in the intended application if possible.
Energy Use and Luminous
Efficacy Luminous efficacy is a measure of how efficient a light source produces visible light and is the ratio of the light output of a lamp (lumens) to its active power (watts). LED lamps have higher luminous efficacy when compared to other lighting technologies. While buying lamps consumers should pay more attention to the luminous efficacy i.e. amount of light the lamp produces per watt than the actual wattage of the lamp. Lamps with higher lumens per watt have higher efficiency.
Rated Life vs. Operational
Life The average rated life of a lamp is determined by the number of hours at which half of the lamps in a large sample are likely to fail and half are likely to survive. LED lamps usually have a rated life of more than 25,000 hours. But, the light intensity of LED lamps decreases gradually with time and it is important to consider the operational life as well when selecting a LED lamp. Operational life can be expressed in terms of lumen maintenance or the ability of a lamp to retain its light output over time. Greater lumen maintenance means a lamp will remain brighter longer. The useful lifetime estimates for LED lighting products are typically given in terms of the expected operating hours until light output has diminished to 70% of initial levels (denoted L70 life)
Dimming/Flicker
Certain lighting applications require dimming capability. The type of dimmers, dimming range, and type of dimming also plays a major part in selecting the lamps. Many LEDs face problems with visual flicker when full on or at any point during dimming. Buyers should be aware of these characteristics before buying the LED lamps. It is also recommended that the consumer be aware of the light output frequency and depth of modulation and know if there is color shift during dimming.