MagicMtnDan
FRF Addict
There are a number of reasons why LED manufacturers’ products differ considerably. Solid-state lighting is a young and developing industry, and innovations are constantly being introduced by manufacturers to improve performance characteristics and to give their products a competitive edge.
Some of the factors that result in product differentiation are:
* The design, manufacture and materials used to create the LED.
* Phosphor development. Different phosphors react differently to heat and to light.
* LED packaging can affect how light exits the package, how much heat can be dissipated and how optics are attached.
So multiple and complex factors within the control of the power LED manufacturer affect the raw performance of their LEDs, with the result that no two brands of LED will perform identically in a luminaire.
This is important to understand, as superficial descriptions of power LEDs can give the impression of a standard output analogous to the standard wattage label applied to GLS bulbs. When two different LED manufacturers describe parts as providing ‘min. 100lm at 350mA’, it is true that, in certain tightly defined circumstances, including but not limited to an input current of 350mA, both power LEDs will produce at least 100lm.
But change those circumstances even a little and the performance of the two LEDs can begin to diverge significantly. The two potentially conflicting key parameters that affect the performance of an LED are:
1. Drive current – up to a certain threshold, the higher the current applied to an LED, the more light it will produce and the hotter it will get.
2. Operating temperature, the hotter an LED gets, the less light it will produce.
These two factors combine to affect light output (lm), efficacy (lm/W), lumen maintenance and ultimately the actual performance of a lighting solution.
No matter which brand of LED a lighting manufacturer uses, luminaire design decisions for drive current and thermal management will entail trade-offs. For instance, a decision to choose a high drive current for higher light output could cut the number of LEDs required to hit the target for light output, which will have a helpful impact on BOM cost. But there will be a trade-off in terms of lower efficacy for the LED and higher operating temperature.
Source: LEDs Magazine - TECH NOTE: Reading between the lines -- how to make accurate performance assessments from a power LED datasheet
---------- Post added at 11:29 PM ---------- Previous post was at 11:27 PM ----------
Candlepower
Candlepower is a measure of luminous intensity when specifically measured in units of candelas. This is like "mileage" is a measure of distance when the unit of measure is in miles.
Candela
Luminous intensity is a measure of light [flux] passing through a unit of *solid angle*. A candela is the intensity produced where there is one lumen [flux] per steradian [the measure of solid angle].
Lux
Lux is a unit of measure of illumination which is a measure of light [flux] *falling on a flat area*. One lux is the illumination produced when there is one lumen [flux] falling on a square meter.
Lumens
Lumens are a measure of total light [flux]. Think of a focusable flashlight. As the beam is adjusted from broad to narrow, the total flux [lumens] stays the same but the illumination of a surface or intensity [lux or candelas] within the beam increases. Illumination [Lux] or candlepower [candelas]can be measured with relatively simple instruments. Flux [lumens] is much more complicated. Most commonly an integrating sphere is used to capture all of the light emitted by a source and then the illumination is measured at a fixed point in the sphere. Through complicated calibrations this illumination measurement is then correlated with a flux value.
Some folks incorrectly think that candelas [candlepower] and lux are units of measure of the same thing but this is not quite correct. It is true that a point source with an *intensity* of one candela will produce an *illumination* of one lux at a distance of 1 meter but this does not make them measures of the same thing.
For example, does a 500 lumen flashlight equate to 500,000 candlepower? No. They are measures of different things.
Source: Newbie Q: Lux vs Lumens vs candlepower
---------- Post added at 11:31 PM ---------- Previous post was at 11:29 PM ----------
Lumens
The lumen can be thought of casually as a measure of the total "amount" of visible light in some defined beam or angle, or emitted from some source. The number of candelas or lumens from a source also depends on its spectrum, via the nominal response of the human eye as represented in the luminosity function.
The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. Mathematically, 1 lx = 1 lm/m2.
Source: http://en.wikipedia.org/wiki/Lumen_(unit)
Lux
Illuminance is a measure of how much luminous flux is spread over a given area. One can think of luminous flux (measured in lumens) as a measure of the total "amount" of visible light present, and the illuminance as a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance is inversely proportional to area.
One lux is equal to one lumen per square meter:
1 lx = 1 lm/m2 = 1 cd·sr·m–2.
A flux of 1000 lumens, concentrated into an area of one square meter, lights up that square meter with an illuminance of 1000 lux. However, the same 1000 lumens, spread out over ten square meters, produces a dimmer illuminance of only 100 lux.
Achieving an illuminance of 500 lux might be possible in a home kitchen with a single fluorescent light fixture with an output of 12000 lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area to the same level of lux requires a greater number of lumens.
Source: Lux - Wikipedia, the free encyclopedia
Some of the factors that result in product differentiation are:
* The design, manufacture and materials used to create the LED.
* Phosphor development. Different phosphors react differently to heat and to light.
* LED packaging can affect how light exits the package, how much heat can be dissipated and how optics are attached.
So multiple and complex factors within the control of the power LED manufacturer affect the raw performance of their LEDs, with the result that no two brands of LED will perform identically in a luminaire.
This is important to understand, as superficial descriptions of power LEDs can give the impression of a standard output analogous to the standard wattage label applied to GLS bulbs. When two different LED manufacturers describe parts as providing ‘min. 100lm at 350mA’, it is true that, in certain tightly defined circumstances, including but not limited to an input current of 350mA, both power LEDs will produce at least 100lm.
But change those circumstances even a little and the performance of the two LEDs can begin to diverge significantly. The two potentially conflicting key parameters that affect the performance of an LED are:
1. Drive current – up to a certain threshold, the higher the current applied to an LED, the more light it will produce and the hotter it will get.
2. Operating temperature, the hotter an LED gets, the less light it will produce.
These two factors combine to affect light output (lm), efficacy (lm/W), lumen maintenance and ultimately the actual performance of a lighting solution.
No matter which brand of LED a lighting manufacturer uses, luminaire design decisions for drive current and thermal management will entail trade-offs. For instance, a decision to choose a high drive current for higher light output could cut the number of LEDs required to hit the target for light output, which will have a helpful impact on BOM cost. But there will be a trade-off in terms of lower efficacy for the LED and higher operating temperature.
Source: LEDs Magazine - TECH NOTE: Reading between the lines -- how to make accurate performance assessments from a power LED datasheet
---------- Post added at 11:29 PM ---------- Previous post was at 11:27 PM ----------
Candlepower
Candlepower is a measure of luminous intensity when specifically measured in units of candelas. This is like "mileage" is a measure of distance when the unit of measure is in miles.
Candela
Luminous intensity is a measure of light [flux] passing through a unit of *solid angle*. A candela is the intensity produced where there is one lumen [flux] per steradian [the measure of solid angle].
Lux
Lux is a unit of measure of illumination which is a measure of light [flux] *falling on a flat area*. One lux is the illumination produced when there is one lumen [flux] falling on a square meter.
Lumens
Lumens are a measure of total light [flux]. Think of a focusable flashlight. As the beam is adjusted from broad to narrow, the total flux [lumens] stays the same but the illumination of a surface or intensity [lux or candelas] within the beam increases. Illumination [Lux] or candlepower [candelas]can be measured with relatively simple instruments. Flux [lumens] is much more complicated. Most commonly an integrating sphere is used to capture all of the light emitted by a source and then the illumination is measured at a fixed point in the sphere. Through complicated calibrations this illumination measurement is then correlated with a flux value.
Some folks incorrectly think that candelas [candlepower] and lux are units of measure of the same thing but this is not quite correct. It is true that a point source with an *intensity* of one candela will produce an *illumination* of one lux at a distance of 1 meter but this does not make them measures of the same thing.
For example, does a 500 lumen flashlight equate to 500,000 candlepower? No. They are measures of different things.
Source: Newbie Q: Lux vs Lumens vs candlepower
---------- Post added at 11:31 PM ---------- Previous post was at 11:29 PM ----------
Lumens
The lumen can be thought of casually as a measure of the total "amount" of visible light in some defined beam or angle, or emitted from some source. The number of candelas or lumens from a source also depends on its spectrum, via the nominal response of the human eye as represented in the luminosity function.
The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. Mathematically, 1 lx = 1 lm/m2.
Source: http://en.wikipedia.org/wiki/Lumen_(unit)
Lux
Illuminance is a measure of how much luminous flux is spread over a given area. One can think of luminous flux (measured in lumens) as a measure of the total "amount" of visible light present, and the illuminance as a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance is inversely proportional to area.
One lux is equal to one lumen per square meter:
1 lx = 1 lm/m2 = 1 cd·sr·m–2.
A flux of 1000 lumens, concentrated into an area of one square meter, lights up that square meter with an illuminance of 1000 lux. However, the same 1000 lumens, spread out over ten square meters, produces a dimmer illuminance of only 100 lux.
Achieving an illuminance of 500 lux might be possible in a home kitchen with a single fluorescent light fixture with an output of 12000 lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area to the same level of lux requires a greater number of lumens.
Source: Lux - Wikipedia, the free encyclopedia
