Question on brightness units for LED's

[jhicks]

Hello,

I've been thinking over for some time about creating a programmable LED display. I have an EEPROM and microprocessor among other things already, so it's not like I'm buying all the parts. Ideally, this display would be viewable from up to 30-40 feet away so it will have license-plate-sized letters. I haven't found an LED display that doesn't already have programmable features in it already so I'm considering building one for myself (yes I know it's a lot of wiring!) but I'm very concerned about finding LED's that are bright enough and have a wide enough viewing angle.

I've looked around Ebay waiting for a good deal on a couple hundred LED's, but units such as "cd" are quite foreign to me and I have no idea how bright 1cd is. http://www.radioshack.com/product/i...&cp=&sr=1&kw=led&origkw=LED&parentPage=search this is 720mcd, but I've bought something like it before and there's no way it would be enough. I found a vendor selling around 100 LED's for 60 bucks that are rated at 100,000 mcd. Is that more appropriate? Thanks.

 

[mgb_phys]

Well 1 Candela is roughly candlelight!
I think you are going to have to do some experiments, it will depend on details of the viewing angle, alignment and lighting conditions - plus the fact that most of the super power LED specifications are lies ( or at least measurements made under rather optimal conditions).

 

[oswaler]

I can provide some insight into the brightness units and considerations for LED's in a programmable display. First, it is important to understand that the unit "cd" stands for candela, which is a measure of luminous intensity. It is a unit commonly used to measure the brightness of a light source, including LED's. 1 candela is defined as the luminous intensity of a light source emitting monochromatic radiation of frequency 540 THz and with a radiant intensity of 1/683 watt per steradian.

In terms of LED's, the mcd (millicandela) unit is often used to measure the luminous intensity. It is equivalent to 1/1000 of a candela. So, for example, 720 mcd would be equivalent to 0.72 cd.

When considering the brightness needed for your programmable display, there are a few factors to consider. One is the distance from which the display will be viewed. The farther away the viewer is, the brighter the LED's will need to be in order to be easily seen. Additionally, the size and viewing angle of the LED's will also affect their perceived brightness. Larger LED's and those with wider viewing angles will appear brighter from a distance.

Another important factor to consider is the ambient lighting in the area where the display will be located. If there is a lot of ambient light, the LED's will need to be brighter in order to stand out.

In terms of the LED's you have found on Ebay, 100,000 mcd is a very high brightness and would likely be suitable for your display. It is always a good idea to do some research and read reviews before purchasing LED's to ensure they meet your needs. Additionally, it may be helpful to consult with a knowledgeable electronics supplier or engineer to ensure you are getting the appropriate LED's for your project.

I hope this information helps in your search for LED's for your programmable display. Good luck with your project!