FAQ

LED Displays

LED Numeric Displays

What is the difference between luminance and luminous intensity?

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.

Is reflow soldering possible for all LED numeric displays?

Reflow soldering is NOT recommended for most LED displays. The only exception is the LF series of surface mount displays. Dip or wave soldering is recommended for all other types (LA/LB/LAP/LBP). Please refer to the respective data sheets for further information.

Is manual soldering possible?

Yes, but please be careful to not apply too much mechanical or thermal stress to the leads, which may affect the reliability. Please consult a ROHM representative for unusual cases.

Are there any storage precautions?

The reliability of LED displays 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.

Is it acceptable to drive LED displays by directly supplying a voltage?

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.

Is it possible to drive LED displays at 1mA?

Yes, provided that a high brightness LED display is chosen. Please ensure that the current flow is stable and does not go below 1mA.

Are there any ways to extend the life of LED Numeric Displays ?

One of the major factors that influence LED display 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

Is it ok to use LED displays outdoors?

LED displays 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.

What will happen to LED displays when they are driven beyond the rated current?

LED display life may be significantly affected. In some cases the luminous intensity my drop for a few hours or may completely turn OFF.

Is it ok to apply water resistant treatment to LED numeric displays that may be exposed to humid environments?

Yes, since LED numeric displays are not normally water resistant. However, this is at the user’s discretion and ROHM cannot provide advice or recommendations regarding this matter or guarantee the effectiveness of such treatments.

What are the precautions when conducting flow soldering?

LED numeric displays, unlike discrete chip LEDs, are housed in larger packages, making them susceptible to damage during preheating. Therefore, it is recommended that preheating during the soldering process is conducted in such a way to ensure that the internal temperature does not exceed 100C. Also, the preheat time should be shortened.

Where are the LED displays manufactured?

In Korea and China (Tianjin).

What is the difference between dynamic and static lighting methods?

Dynamic lighting signifies pulse or duty lighting, meaning that the device is lit using pulses and not continuously powered. The advantages include lower current consumption and longer life, while a disadvantage is more complicated circuit design. Static or DC lighting refers to lighting a device using a continuous supply of power, which shortens the life and consumes more power but is simpler to design.