LED HEAT DISSIPATION TECHNOLOGY
The most important point about the design of the LED High Bay is:
LED chip design and control of the LED junction temperature.
LED Driver rating and Driver Position
Heat control of the LED fitting
1 LED Chip:
High powered LEDs can use much power. Most of the electricity in a Led becomes heat rather than light (70% heat and 30% light). If this heat is not removed the LED source will run at high temperatures, which lowers there efficiency and makes the LED light less reliable. Thus heat management of high power LEDs is crucial. It is necessary to keep the LED junction temperature below 120 Deg c to enable a long life for the LED light.
Most LEDs are encapsulated in a resin, which is transparent, but this is a poor conductor of heat. Nearly all the heat is conducted through the back side of the LED chip. Power generated from the LED junction (PN junction), that does not generate light must be conducted away to the PCB board and then to a heat sink and then into the air. The thermal resistance from the LED junction to the air MUST BE MINIMISED.
A perfectly flat contact area where the light source PCB mounts to the heat sink, allows the use of a thin layer of thermal compound to reduce the thermal resistance between the heat sink and the LED source. This is very important.
2 LED DRIVER:
Isolation of the LED driver from the LED board prevents the driver from raising the LED junction temperature at the LED source and stops the LED source heating the LED driver. The LED driver high operating ambient (60 Deg C say) and driver operating temperature (90 Deg C total temperature). Other wise the LED diver will fail under high ambient temperatures.
3.HEAT CONTROL OF THE LED FITTING:
One of the most interesting points that are important to the longevity of the LED high bay fitting is:
The control of the extraction of the heat from the LED source of the LED light to the heat sink.
Some new developments are the use of “heat pipes” that have special capability to conduct the heat from the LED chips to the radiator.
The heat pipe makes use of a super conductor of heat to rapidly extract the heat away from the LED source. This is the secret to longevity of the LED light source. Lower temperature means longer light source life. LED chips do not like the high temperatures.
The heat pipe is the newest technology to be used to minimise the heating of the LED chips.
The heat pipe works on a technology that uses a copper pipe with vacuum and capillary action to maximum the instantaneous conduction of the heat away from the heat source and delivers it to the radiator or heatsink.
COOLING AFFECT OF THE HEAT PIPE WHEN USED WITH A HIGH POWER LED LIGHT:
THE HEAT TRANSFER OPERATION OF THE HEATPIPE:
Please see the latest design of high bays using this technology on the Tortech Lighting website.
The other important point is the efficiency of the heat sink.
The heat sink provides a path for the heat to travel from the light source to the surrounding air.
There are three methods of heat transfer:
Conduction( heat transfer from solid to solid)
Convection (heat transfer solid to a moving fluid)
Radiation (heat transfer from two bodies of different temperatures through thermal radiation)
Important aspects of the heat sink design are
A) Material: Normally aluminium is used as it has a low thermal resistance. Copper can also be used but is more expensive.
B) Shape: There needs to be a large thermal dissipating area. Use of a large number of fins increase or a large size of the heat sink itself
C) Surface finish. A painted surface has a greater emissivity than a bright unpainted one.
D) That is it increases the ability of the surface to radiate the heat away from the heatsink.
Painting the surface matt black increases the black body radiation capability of the heat sink.
This further increases the emissivity . This is significant and is important improvement to the heatsink’s efficiency.