Functional Lighting with White LED
LED is new generation light source and having it’s own merits over the conventional light
sources. Long life ( If luminaire and driver designed properly), Almost no maintenance, Energy
efficiency, Robust and Vibration proof nature, Controllability, Flicker free switch on, Free from
Infra red and Ultraviolet radiation in beam, No mercury, Low Voltage application and
compactness are main advantages of using LEDs as light source.
LED as a technology is now commercially available to be applied in functional lighting (Using
white LEDs) also. Since LEDs are directional therefore much better optical control is possible in
designing functional lighting luminaire, this directional nature of light source as LED helps to
reduce wastage of luminous flux within the luminaire hence improves the efficiency of each
individual luminaire.
LED based lumianire not only help to improve visual environment but also helps to conserve lot
of electrical energy for same visual performance. LED light source also help to avoid pollution
because it does not have any mercury content.
LED based direct diffused lighting helps to achieve in brightness management as it distribute
light not only on work plane but also on wall. This approach of volumetric lighting helps to
create visually better illuminated environment and avoids cave effect being achieved through
direct lighting luminaires.
There is myth that LEDs generate a lot of heat. Actually LED operating surface temperature is
high compare to Fluorescent technology based lamps because in LED power management is in
a very small area compare to much more surface area of FLUO lamps.
Let us take a quick view as below on heat related calculations to support above argument.
Heat Load Calculations for 4 x14 W T5 Fluorescent Luminaire Vs 25 / 36 LED
Luminaire
Energy Balance Diagram for Discharge Lamp
When electrical energy is given to any discharge lamp, the electrical energy mainly gets
distributed in three parts:
-
Losses within Lamp
Conversion to Light Spectrum
Heat Losses
The Correlation between Input Energy and Distribution of input energy in various output
parameters is called Energy Balance Diagram. In order to calculate impact of Heat
generated by discharge lamp on heat load in interiors, Energy Balance Diagram can be
effectively used. Each Discharge lamp type has individual Energy Balance Diagrams.
Energy Balance Diagram for Conventional Fluorescent Lamp:
Input Energy: 100 %
Output Energy Distribution
Power Losses at Tube – 34.0 %
Electrode Losses – 16.5 %
Non Electrode Losses – 17.5 %
Power Losses in Phosphor Layer – 0.5 %
UV radiation (escaping from tube) – 37.5%
Visible Radiation – 28 %
This means in case of Conventional Fluorescent lamp ( with Halo Phosphor), only 28 % of input
energy gets converted into light, while 72 % of input energy gets converted in to heat.
Energy Balance Diagram for T5 Lamps:
For High Efficiency T5 Lamps, the equation changes due to use of Tri-Band Phosphor with
better UV conversion efficiencies into while light. For T5 lamp, the Energy Balance Diagram is as
under:
Input Energy: 100 %
Output Energy Distribution
Power Losses at Tube – 34.0 %
Electrode Losses – 16.5 %
Non Electrode Losses – 17.5 %
Power Losses in Phosphor Layer – 0.5 %
UV radiation (escaping from tube) – 29.5%
Visible Radiation – 36 %
Apart from the above entire power consumed in electronic ballast is converted into heat.
The above Energy Balance Diagram is considered for Florescent and T5 Lamp usage using
electronic Gear.
Effect of Energy Balance Diagram for T5 lamps on Heat Load Calculations:
In case of T5 Lamp, approximately 64 % of input energy is converted into heat energy. If this is
translated in electrical wattage for various T5 lamps then the scenario emerges as under:
14 W T5 – 9W of input Energy converted into heat
28 W T5 – 18W of input Energy converted into heat.
Heat Load Generated by 4 x 14 W T5 Luminaires:
Considering the above, the Heat generated by 4 x 14 W T5 Luminaire would be:
Wattage of Lamp – 14 W
No of Lamps – 4 Nos
Total Wattage of all four lamp – 56 W
Lamp Wattage converted into heat – 36W (9W per Tube)
4x14 W T5 Electronic Ballast Watt Loss converted into heat – 8 W
Total Input Wattage converted into heat in case of 4 x 14 W T5 Luminaire – 44 W
BTU/Hr Conversion due to Electrical wattage converted into heat
Wattage to BTU/Hr conversion formula is as under:
1 W = 3.4144 BTU/Hr
Hence, 44 W of wattage which gets converted into heat in case of 4 x 14 W T5
Luminaire will translate into 150.26 BTU/Hr
Heat Generated by LED
Light Emitting Diode is a semiconductor device and does not use mercury or any other metals
and hence it does not generate UV or IR in the direction of light beam during operation. Hence
LED Modules do not generate any heat in the direction of Illuminated object. The only heat
generated in LED is due to power consumption in LED (Resistance of LED x current into LED).
Since the LEDs are of very small size, though LEDs do not generate very high heat, whatever
small heat is generated by LEDs is mainly concentrated at very small LED Junction.
LED Luminaires are mainly cluster of small wattage (normally of wattage of 1 to 6 W) LEDs.
Also the LEDs in cluster are distributed over large surface with effective heat sink mechanism,
which ensures that heat is effectively distributed and removed from LED junction quickly.
Considering the above, there are no Energy Balance Diagrams for LEDs.
However as LED Luminaires consume electric power, in worst case scenario, we can consider
the complete LED wattage and power consumed in LED Drivers for Heat Load Calculations.
To effectively replace 4 x 14 W T5 or 4 x 18 W T8 Luminaire, we can either use 25 W LED
Luminaire or 36 W LED Luminaire.
Total Electrical Wattage consumption in 25 W LED Luminaire:
No of LEDs in Module: 25 Nos.
Nominal Forward voltage of each LED: 3.2 V
Nominal Forward Current of each LED: 350 mA
Total Wattage of each LED : 3.2x0.350 = 1.12W
Total Wattage of 25 LED Cluster Module: 1.12 W x 25 = 28 W
Power Consumption in LED Drivers: Approx. 6 W
Total Power Consumption for 25 LED Module including Driver = 34 W
Assuming entire 34 W of LED power is leading to heat generation, total heat
generated by 25 LED Luminaire will be 116.01 BTU/Hr
From the above it can be seen that the total heat load in case of 25 LED Luminaire is in far
excess of heat generated by 4 x 14 W T5 Luminaire.
Total Electrical Wattage consumption in 36 W LED Luminaire:
No of LEDs in Module: 36 Nos.
Nominal Forward voltage of each LED: 3.2 V
Nominal Forward Current of each LED: 350 mA
Total Wattage of each LED : 3.2x0.350 = 1.12W
Total Wattage of 36 LED Cluster Module: 1.12 W x 36 = 40 W
Power Consumption in LED Drivers: Approx. 8 W
Total Power Consumption for 36 LED Module including Driver = 48 W
BTU/Hr Conversion due to Electrical wattage converted into heat
Wattage to BTU/Hr conversion formula is as under:
1 W = 3.4144 BTU/Hr
“Assuming” entire 48 W of LED power is leading to heat generation, total heat
generated by 36W LED Luminaire will be 163.89 BTU/Hr.
Instead of these complex calculations in terms of energy balance diagrams and then
conversion in BTU/Hr, in simple terms, since LED Luminaires consume lesser power
than 4 x 14 W T5 Luminaires, the total heat generated which will affect Heat load
calculations will be lower.
Total Power consumption in 4x 14 W T5 Luminaire : 64 W
Total Power Consumption in 25 LED Module: 34 W
Total Power Consumption in 36 LED Module: 48W