1) Unit of measure
- Light (symbol: lm) is the unit of the international measurement system for measuring the luminous flux, a measure of the luminous flux emitted by the source.
- The lumen per watt (symbol: lm / W) is the unit of the international measurement system for measuring the luminous flux per watt of electrical consumption from the emitting source.
2) Efficiency of LEDs
The efficiency of the LED can be expressed in both lumens and lumens watt, it must be taken into account that if it is expressed in lumens watt, we cannot know directly if it is a single LED of a watt of power or a set of LEDs which add a total of one watt of power.
For example, a single LED of ≈0.33 watts of power has a luminous efficacy of 58lm or 174lm / W, because we will need three units to consume one watt of power (0.33W * 3 = 1W), therefore 58lm * 3 units = 174lm / W.
The luminous efficiency of an LED is a quality parameter. If we know the efficiency of the LED and have the data sheet, we can know the constraint that the LED can be submitted in the luminaire.
The efficiency of the LED depends directly on the electric current to which it is subjected, for the same model and the same brand of LED, the manufacturer provides us with a light efficiency curve as a function of the electric current that we supply to the LED. The same CHIP LED at higher current, greater efficiency but greater stress and deterioration due to temperature .
Therefore, if an LED can operate between 10 and 200 mA and we operate it below the typical current (1: 1), we will not get the maximum light efficiency, but we will increase the durability of the LED.
Image -1- (OSRAM DURIS® S5 LED, GW PSLR31.EM ≈136lm, implemented in our MaxCam LED high bay).
Our MaxCam LED is an LED designed to extend its lifespan, each of its LED chips is powered at an approximate current of 60mA, well below the typical current (150mA) that Osram uses in its graph as a factor 1:1.
In the case of the MAxCam LED high bay, the factor is 0.43
Efficiency MaxCam LED = 136 * 0.43 = 58.48 lm, since we need three LEDs for 1 watt of power, we can express it as 58.48 * 3 = ≈175 lm / W.
Real test of a single LED of our MaxCam LED, where the theoretical calculations exposed can be corroborated:
Knowing the power of the LED (technical sheet of the manufacturer of the LED) and the efficiency of the LED, we can perform the calculation backwards and know how much of the working curve the LED works, so get an idea the quality and durability of the luminaire in relation to the life of the light source.
3) Efficiency of the luminaire
The luminous efficiency of the luminaire or of the luminous system, gives us a value in lm or lm / W which will be the real contribution of all the elements that make up the luminaire, mechanical and electronic obtained at the time of the test, but in no case does it will provide us with solid value to assess the quality of the fixture.
Take as an example that in our MaxCam LED we power the LED at 100mA instead of 60mA, we are still below the typical current that Osram establishes as a 1: 1 factor of 150mA, in return, the result of efficiency The luminaire's luminosity is considerably increased despite its lifespan.
Efficiency MaxCam LED (100mA) = 136 * 0.70 = 95.2lm, as we need three LEDs for 1 watt of power, we can express it as 95.2 * 3 = ≈285lm/W.
If at this value we apply between 20 and 25% of losses due to the implantation of the LED in the luminaire, we obtain an efficiency of the lighting system or luminaire of 214lm / W !!.
Case study
It is said that an extra flat LED high bay with an OPAL diffuser, with the same model and the same LED brand, provides more light than our LED high bay and is cheaper.
If the high bay is made with the same model and the same brand of LED, but it produces more light it can be due to two parameters:
1) Less loss of efficiency of the luminaire (Not applicable: an OPAL diffuser has much more loss).
2) The working current of the LED is greater, (Corresponds: greater efficiency which compensates for the losses of the OPAL diffuser).
Why is it cheaper?
1) It is extra flat, they have reduced costs by reducing the quantity of refrigerator (aluminum), contrary to what would be necessary, increase the refrigerator because there is more heat to dissipate.
2) It is driverless, which means it has no driver or power supply, more exposed to electrical disturbances and with high frequency flicker.
Being an LED luminaire with a low profile refrigerator, it dissipates less heat and, by working with a higher current intensity, the lifetime of the luminaire is reduced by heating more and not having good cooling.
As a result, the most economical extra flat LED high bay, with OPAL diffuser, greater luminous efficiency of the light system or luminaire had a warranty of only two years, unlike our LED high bays which all have a warranty of five years.
Conclusions:
1- The efficiency of the light system or luminaire only gives us a value at an "initial moment".
2- The efficiency of the lighting system does not guarantee or provide any data that allows us to assess the quality of the design and implementation.
3- A luminaire with an efficiency of the luminous system, apparently greater and the same LED model implemented will suffer more stress and deterioration due to the temperature.
4- The efficiency of the LED and its technical characteristics allow us to have an idea of the quality and durability of the product.