Luminous intensity refers to the overall brightness, from a lamp LED, for example, without regard to the area of the light source. Luminance indicates the degree of brightness over an area, such as from a display device. The greater the source area the higher the luminance. The luminance is normally obtained by dividing the luminous intensity by the light source area.
No, some LEDs should not be reflow soldered. Chip LEDs are suitable for reflow, while lamp types (through-hole/leaded) should be flow or dip soldered. Soldering conditions and information are contained in the respective data sheets, and vary by manufacturer.
The reliability of LEDs can be compromised by moisture absorption, which can lead to failures during the soldering process. For this reason humidity control is highly recommended. Please refer to the respective data sheets for additional information.
Although possible, it is not recommended, since directly supplying voltage may, as we have seen above, result in an exponential change in output current, which can cause failure. Therefore, resistors should be connected to limit current.
One of the major factors that influence LED life is die temperature – the lower the temperature the longer the life. In order to maintain low LED die temperature the following should be heeded: •Keep current flow small •Minimize ambient temperature •Design for sufficient heat dissipation
LEDs in general are not designed to be used outdoors. Adequate moisture treatment, temperature management, UV filtering, salt air protection, and the like should be provided if intended for outdoor use.