Indirect Lighting & Energy Conservation Part 7
6.1 ADVANTAGES OF LED:
Reduced Maintenance Costs: LED based light sources last at least 10 times longer than a normal light source.
More Energy Efficient—Be the Environmental Solution: LED light source are more efficient than incandescent and most halogen light sources.
Design Flexibility and Unobtrusive Hidden Light: LEDs are typically much smaller than conventional light sources, allowing for dramatically different lighting designs capitalizing on the unobtrusiveness of the source.
Vivid Saturated Colors—Without Filters: Light Emitting Diodes require no filters to create colored light, resulting in deeper saturated colors without
wasted light.
Directed Light for Increased System Efficiency - The light emitted from an LED is directional. Typical conventional sources such as incandescent, halogen, or fluorescent lights are omnidirectional, emitting light in all directions
Instant On, Full Color, 100% Light- Light emitting diodes have turn on times measured in microseconds.
No Mercury in the Light Source- Unlike most fluorescent sources, LEDs contains no Mercury. Eliminating Mercury from your lighting system will enable you to meet new and future increasingly stringent environmental regulations.
No Heat or UV in the Light Beam - Conventional light sources (as well as some LEDs) contain invisible radiation as well as the visible component of light in the beam. Infrared light can damage displayed objects, increases air conditioning costs, decreases environmental comfort,
and when reflected off reading surfaces increases eyestrain.
Cold Start Capable - Many light sources in use today are not well suited to cold environments. The cold start ability allows for instant on/off control without specially designed circuitry, simplifying your system design while lowering the cost of the electronic driver.
Low Voltage DC Operation - Unlike conventional light sources, light emitting diodes are current driven low voltage devices. This enables never before solutions that meet regulatory requirements without expensive safety interactions.
How Much Energy Does an LED Emit?
The electric energy is proportional to the voltage needed to cause electrons to flow across the p-n junction. The different colored LED's emit predominantly light of a single color. The energy (E) of the light emitted by an LED is related to the electric charge (q) of an electron and the voltage (V) required to light the LED by the expression: E = qV Joules. This expression simply says that the voltage is proportional to the electric energy, and is a general statement which applies to any circuit, as well as to LED's. The constant q is the electric charge of a single electron, -1.6 x 10-19 Coulomb.
Finding the Energy from the Voltage - Suppose you measured the voltage across the leads of an LED, and you wished to find the corresponding energy required to light the LED. Let us say that you have a red LED, and the voltage measured between the leads of is 1.71 Volts. So the Energy required to light the LED is E = qV or E = -1.6 x 10-19 (1.71) Joule, since a Coulomb- Volt is a Joule. Multiplication of these numbers then gives E = 2.74 x 10-19 Joule.
7. MEASUREMENT OF ILLUMINANCE:
Illuminance (Unit – Lux, Symbol - E) The luminous flux reaching the working plane per unit of area is called the illuminance. For the magnitude of illuminance it does not matter the direction form which the luminous flux reaches the plane. The illuminance is a scalar quantity. The illuminance on a plane due to one light source and due to another source on the same plane can therefore be added to arrive at a total value.
If the luminous flux is not uniformly distributed over the plane, one has to work out average illuminance (Eav) on that plane. The illuminance on the working plane is therefore the result of direct as well as reflected light.The symbol of illuminance is E and unit is as follows:
In Metric System , Illuminance E = /A lumen/m2 or Lux It is Measured with help of Lux meter