LEDs are like tiny lightbulbs. However, LEDs require a lot less power to light up by comparison. They're also more energy efficient, so they don't tend to get hot like conventional lightbulbs do (unless you're really pumping power into them). This makes them ideal for mobile devices and other low-power applications. Don't count them out of the high-power game, though. High-intensity LEDs have found their way into accent lighting, spotlights and even automotive headlights!
LEDs emit more lumens per watt than incandescent light bulbs. The efficiency of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes.
LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond.
In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED.
LEDs can have a relatively long reliable life. The LED lifespan is measured in hours with the associated percentage of light output, noted as Lp. In other words, L70 of 30,000 hours means that the tested LEDs produce 70% of the initial light output at 30,000 hours
Think of lumens as a "new" way of knowing how bright a lamp is. Lumens = Light Output
This figure is a useful way to measure the efficacy of lighting products by measuring the total light output in Lumens divided by the power usage in Watts. You can think of this as similar to miles-per-gallon in a car, as a higher lm/W means higher efficiency and lower running costs compared to similar but less efficient models.
The Color Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a "given" light source is at rendering color when compared to a "reference" light source. The higher the CRI, the better the color rendering ability.
To read the graph, imagine the LED is standing upright underneath it. The "spokes" on the graph represent the viewing angle. The circular lines represent the intensity by percent of maximum intensity. This LED has a pretty tight viewing angle. You can see that looking straight down at the LED is when it's at its brightest because at 0 degrees the blue lines intersect with the outermost circle. To get the 50% viewing angle, the angle at which the light is half as intense, follow the 50% circle around the graph until it intersects the blue line, then follow the nearest spoke out to read the angle. For this LED, the 50% viewing angle is about 20 degrees.
Kelvin is a unit of measurement used to describe the hue of a specific light source. The higher the Kelvin value of the light source, the closer the light's color output will be to actual sunlight. Bulbs with an output of 3500K or lower on the scale will have an amber hue.