There are two primary ways of producing high-intensity white-light using LEDs:
A lumen (used to measure the brightness of LED) is about the equivalent of the amount of light put out by a single birthday candle if you are one foot away from the candle. A lamp that puts out 1 lumen of light is as bright as one birthday candle a foot away
The theoretical maximum for green LEDs is at 683 lumens per watt but today few Green LEDs exceed even 100 lumens per watt.
LED's current is dependent exponentially on the voltage. A small change in voltage can cause a large change in current. If the maximum voltage rating is exceeded by a small amount, the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. The typical solution is to use constant-current power supplies
Most manufacturers’ published ratings of LEDs are for an operating temperature of 25 °C. LED light output rises at lower temperatures, leveling off depending on type at around −30C
Two aspects of energy efficiency are important to consider: the efficiency of the LED device itself(source efficacy); and how well the device and fixture work together in providing the necessary lighting (luminaire efficacy)
LEDs lighting quality depends on:
Color appearance. Color appearance is measured by correlated color temperature (CCT) on the Kelvin (K) scale. For most interior lighting applications, warm white (2700K to 3000K) and in some cases neutral white (3500K to 4000K) light is appropriate.
Color rendering. The color rendering index (CRI) measures the ability of light sources to render colors, compared to incandescent and daylight reference sources. The leading high-efficiency LED manufacturers now claim a CRI of 80 for phosphor-converted, warm-white devices. In general, a minimum CRI of 80 is recommended for interior lighting.