Questions about LEDs?

1. Q: What is the brightness, viewing angle and wavelength of the LED?

A: Luminous Intensity is equal to the amount of luminous flux emitted into a very small solid angle at a defined angular orientation from the light source. The measurement for luminous intensity is the candela. Symbol is Iv.

Viewing Angle is the total cone angle in degrees encompassing the central, high luminous intensity portion of the LED beam from the on-axis peak to the off-axis point where the LED intensity is 50% of the on-axis intensity. This off-axis point is known as theta one-half (θ 1/2). Two times θ1/2 is the LEDs’ full viewing angle; however, light is visible beyond theθ1/2 point.

Wavelength is the distance between two points of corresponding phase and is equal to waveform velocity divided by frequency. It defines what color human eyes could recognize.

2. Q: What is dominant wavelength? Please specify the ranges of wavelength in red, green and blue color respectively.

A: Dominant wavelength is defined as the best range of wavelength showing the most natural color recognized by human eyes. Researches indicate that fixed colors with wavelength of 620-630nm (red), 520-530nm (green) and 460-470nm (blue), in fact mixed in a particular proportion, can get the pure white. That is, in display field, people use luminous materials with above wavelength to make “compounded” white more natural.In order to get a good balance white led display, we specify the led colors with wavelength within 4nm for each color.

3. Q: Which chip vendors are you buying from?

A: It depends on the Customer’s requirement. We can purchase from Japan, Korea, Europe, USA. We are using chips mainly from Taiwan.

4. Q: What is the chip size you’re using for outdoor display? How about indoor display?

A: For outdoor display, we’re using 12mil chip for red, 14mil for both green and blue. Regarding indoor display, 9mil for red, 12mil for green and blue are currently adopted.

5. Q: How much will the brightness of LED drop down after 1000hrs?

A: Based on the result of aging test, the brightness decay of green LED is around 5%-8%, while blue is around 10%-14% and red is around 5%-8%.

6. Q: What is the ESD withstanding capacity of your LED? How do you do to SHENZHEN LAMP TECHNOLOGY CO.,LTD FAQ-1.0V(2009) protect LED from damaging by electrostatic?

A: Normally we’re using chips made of sapphiric substrate with the ESD withstanding capacity 500v. Compared with Cree chip which is made of SiC substrate, it is weaker and easily damaged by electrostatic. Thus we place great emphasis on overall aspects through the whole procedure, involving producing, storing and using. For instance, whoever in touch with LED lamps directly or indirectly is supposed to wear antielectrostatic gloves and wrist band.

7. Q: What is the lifespan of LED?

A: 100,000hrs.

8. Q: How do you ensure the color and brightness evenness of LED screen? Can you still offer us same modules even after long time from first order?

A: Before packing, all LED lamps will be sorted into preset bins based on appointed wavelength, brightness and voltage. Since the spacing of rightness and wavelength is narrow, for instance we supply 1:1.1 for spacing of brightness while Nichia offers 1:1.4; we can make color and brightness of LED screen look consistency and evenness by adopting those selected LED lamps.We’ll trace the archive files for the record of first order, definitely it will be of great help to use same parameter LED lamps. However, it is still hard for us to make exact same modules since LED lamps would be slight different with previous ones more or less. Let’s say 80%-90% match.

9. Q: What is the material of lead frame? Iron or Copper?

A: For DIP LED lamps used for outdoor display, iron is currently used for lead frame; for SMD LED, it will be copper.

10. Q: What is the difference between Silan chip and Taiwan chip?

A: As we all know, there are a great deal of chip venders in Taiwan offering dice in different grades. Among them, Silan is supposed to be in the medium-up group, involving brightness, degradation, reliability and price. For instance, compared to the same size chip from Huga, Silan's chips are with slight lower brightness and price. However, both of them are stable and less degradation.

Normally we will select different chips based on products in different applications. For instance, we are using Epistar chip of 14mil for outdoor display use while Chi Mei's chip for white SMD LED which.

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