LED Products Frequently asked questions

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What is the difference between the Mechanical Center and Optical Center?
When LEDs are placed into a typical test fixture, it is usually placed in such a way as to assume the light is emanating from the device's mechanical center.   

In general terms, what is the difference between Radiant/Luminous Flux and Radiant/Luminous Intensity?
Stated briefly, Radiant/Luminous Flux represents the total emitted optical power generated by a light source that is collected and measured with no regard to the direction of the flux.   

What is the difference between Photometry and Radiometry?
Before describing the difference, it is important to note that the human visual range is typically from 380nm to 780nm.   

What is the difference between Dominant and Peak wavelength?
Dominant wavelength is the single wavelength that is perceived by the human eye, and is defined as the wavelength of monochromatic light that has the same apparent color as the light source.   

Can you give a brief overview on LED die material and application usage?
GaP (Gallium Phosphide), Typically used in standard green and red LED's   

What are the catastrophic failure mechanisms for LEDs?
Mechanical overstress induced by high temperature is the most common cause of failure in LEDs.   

What does "LED life" mean?
All LEDs lose brightness (degrade) over time.   

Can I increase light output by pulsing LEDs at low duty factors and high peak currents?
The advantage of pulse modulated lighting is the reduction in the LED's power dissipation, thus prolonging the life of the battery or increase the perceived brightness.   

Can LEDs be driven directly from a voltage source?
It is not recommended to apply a direct voltage source to an LED without a current limiting resistor or source even though the LED appears to be functioning correctly.   

Can I increase light output indefinitely by increasing the forward current?
Light output will increase as input current increases, however only up to a certain point. As the current increases, heat generation will increase as well.   

Can I base my design around Absolute Max Ratings?
The Absolute Maximum Ratings are rated values which must not be exceeded during operation, even for an instant.   

How do LEDs respond to different temperatures?
Luminous intensity (brightness), wavelength (hue or color), and forward voltage are the three main parameters of an LED that are affected by temperature.   

What precautions should be observed in my thermal design?
The failure rate of semiconductor devices is greatly accelerated as operating temperatures increase.

What can affect the Junction Temperature of LEDs?
The following parameter's affect the junction temperature of LEDs Thermal resistance between junction and package surface, or internal thermal resistance (¡ãC/W). Typically denoted as "¦¦jc"