20 facts you should know about LED. What is LED? What is Luminous Flux? What is Color Rendering Index (CRI)? How to choose the right Beam Angle?
Acronym for light-emitting diode, a solid-state component that emits light when exposed to electric current. LED lighting represents the state-of-the-art in the industry, outclassing most other types of lighting in terms of energy efficiency, design flexibility and colors of light available.
Total output emitted by a light source, measured in lumens. The luminous flux describes the total lighting output of a lighting fixture without considering direction. Not to be confused with luminous intensity.
Lumen Maintenance Life
A metric used to describe the time in which the output of a lighting product diminishes to a specific percentage of its initial value. The lumen maintenance life is measured in hours and displayed by the letter L plus two digits. For example, the following lumen main tenance life would describe a product whose output decreases to 70% after 60,000 hours of use: • L70 = 50,000 hours
The luminous flux on a surface, per unit of area. The illuminance requirements of built environments are determined by their intended purpose, and there are two common units of measurement: • Lux - Equivalent to one lumen per square meter. • Foot-candle - Equivalent to one lumen per square foot. Higher illuminance levels make surfaces appear brighter to the human eye and improve visibility.
Lighting emission in a specific direction, measured in candelas. Luminous intensity changes depending on the viewing angle. Not to be confused with luminous flux.
The brightness of an object or surface, as perceived by human eyesight from a specific direction. Luminance is measured in candelas per square meter (cd/m2). It is important to note than luminance changes depending on the viewing angle, and high luminance values are the direct cause of glare.
Also known as beam spread, the beam angle is a value that describes the downward light cone emitted by a lighting fixture with a reflector. The beam angle is measured between the downward direction, where the lamp provides maximum lighting intensity, and the direction in which intensity drops to 50%. In other words, a lamp with a large beam angle spread its lighting into a wider cone.
Color Rendering Index (CRI)
A metric used to describe how faithfully a light source can render the true colors of objects and spaces, where natural light sources like the sun have a perfect index of 100. Using lamps with a high CRI value is very important in high-end interior design, as they enhance the visibility of décor and fine details.
Correlated Color Temperature (CCT)
Color temperature of a light source is the temperature of an ideal black-body radiator (solid object with certain properties heated up to point of incandescence) that radiates light of comparable hue to that of the light source, and its temperature is expressed in Kelvins (K). As a black body gets hotter, wave lenght of light emits progress through a sequence of colors from red to blue Sequence of colors is described by curve (Planckian locus) within a CIE 1931 color space
Conversion ratio between lighting power output and electric power input, measuring both quantities in watts. Not to be confused with efficacy, which describes the ratio between lumen output and watts consumed.Since lumens describe lighting output better than watts, efficacy tends to be a much more useful concept in lighting design.
Visual impairment caused by a bright source of light, directly visible or reflected by a surface. There are two types of glare:
• Discomfort glare causes an instinctive reaction to close the eyes and look away. This is the type of glare felt when exposed to a potent HID light or when the sun is directly visible through a window.
• Disability glare impairs vision, but does not cause the same reaction as discomfort glare. If a light source gets reflected on your laptop screen, for example, it does not bother your eyes but distinguishing objects on the screen may be impossible.
UGR(Unified Glare Rating)
Classifies the discomfort glare caused by an indoor lighting system, taking into account the kind of luminaires, the reflecting features and size of the rooms, the position of the observers. ”
UGR / Discomfort Degree
28 / Severely Dazzling
25 / Dazzling
22 / Blinking
19 / Unconfortable
16 / Slightly Unconfortable
13 / Perceptible
Viewing angle beyond with it is no longer possible to see a light source directly, measured from the direction exactly below the lamp (nadir).
Acronym for Digitally Addressable Lighting Interface, a communication protocol for lighting automation.
Piece of electronic equipment that transforms the main supply voltage into a lower DC voltage that is appropriate for LED lighting. Some LED lamps have a built-in driver, while others require one to be connected externally, just like the ballasts used by fluorescent and HID lamps.
Power Factor (PF)
Ratio of real power to apparent power drawn by lighting fixtures and other electrical devices. The real power is represented by the actual watts consumed, while the apparent power is the multiplication product of voltage and current, measured in volt-amperes. Electric utility companies normally apply additional charges if the power factor of a building drops below a specified level.
Conversion ratio between lighting power output and electric power input, measuring both quantities in watts. Not to be confused with efficacy, which describes the ratio between lumen output and watts consumed. Since lumens describe lighting output better than watts, efficacy tends to be a much more useful concept in lighting design.
A phenomenon where a lamp blinks repeatedly, often caused by power supply issues, or a faulty ballast or driver.
Conversion ratio between lighting power output and electric power input, measuring both quantities in watts. Not to be confused with efficacy, which describes the ratio between lumen output and watts consumed.
Since lumens describe lighting output better than watts, efficacy tends to be a much more useful concept in lighting design.
Dimming method that uses incremental and fixed lighting levels, as opposed to gradual dimming from OFF to 100% output. See Dimmer.
Lighting effect where a wall with an irregular surface is illuminated so that there are both highlighted and shaded areas. This effect is only possible on walls with granular surfaces, such as those built from stone or exposed brick. The opposite effect is wall washing.
Lighting effect where a wall is illuminated so that surface irregularities are minimized, it seem smoother. The opposite effect is wall grazing.
Lighting designed to provide visibility when the normal lighting system fails, for example during blackouts. Emergency lighting is equipped with batteries, allowing it to operate long enough for a building to be evacuated.