Choosing correct LED mcd for outdoor indication

  • Thread starter peterlonz
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In summary, the low output, 12 mcd, LED is not very bright. It is designed for outdoor use but may not be able to withstand the sun's radiation. A brighter LED with more output, like the 5000mcd option, is available for a slightly higher price.
  • #1
peterlonz
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I don't wish to ask dumb questions about basic LED applications but ...
Yesterday I bought a 12 mcd, 5mm Dia, red LED, through hole mount.
It was to replace an unexpected failure of the previous unit: supposed to suit 12VDC supply & containing a built in resistor.
The application is a 12VDC regulated, 2 amp capable, PSU.
The original LED was nice & bright & easily seen outdoors.
This was good because the 240VAC power on/off rocker switch containing a red neon is not sufficiently bright
My replacement LED is relatively dim & I need to cup my hand over it (when outdoors) to be sure its on.
Now by chance I made a silly mistake & used a 100 ohm resistor instead of the 300 Ohm which is what I calculated should be used.
So I am expecting the LED to fail soon, but it should be much brighter surely with the higher current.
I can't figure out this dilemna.
I suspect 12 mcd (@ $0.25 ) is probably a poor choice but there seems very little choice between this low output & the much higher rated 5000 mcd & above.
Suggestions please?
 
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  • #2
Yes, that is a very low powered LED. 1 Candela is roughly the brightness of one candle.

So 12 mcd is about 1% of 1 Candela. Not much.
5000 mcd is 5 candles, so, much better.

You can get a brighter LED and just run less current through it. They are usually highly efficient, so try calculating the resistor with 20 mA flowing in it. Maybe 470 ohms.
 
  • #3
I'm thinking you're shopping at the wrong place. You can get pretty much any LED you can imagine! I like shopping at Digikey (http://www.digikey.com) for parts.

5000mcd isn't really that much. Remember, a candle is 1000mcd.

Here's what I'd go with: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=C4SMF-RJS-CT0W0BB2CT-ND

Rating is 2640mcd price $0.20

From the Datasheet.
This oval LED is specifically designed for variable-message signs and passengerinformation
signs. The oval-shaped radiation pattern and high luminous intensity
ensure that these devices are excellent for wide-field-of-view outdoor applications
where a wide viewing angle and readability in sunlight are essential.
These lamps are made with an advanced optical-grade epoxy that offers superior
high-temperature and high-moisture-resistance performance in outdoor signal
and sign applications. The encapsulation resin contains anti-UV material in order
to reduce the effects of long-term exposure to direct sunlight.
 

1. How do I determine the correct LED mcd for my outdoor indication?

The correct LED mcd for outdoor indication depends on the distance of the indication and the brightness required. Generally, a higher mcd rating will result in a brighter LED. However, it's important to consider the viewing distance to avoid excessive brightness that can be uncomfortable for viewers.

2. Is a higher mcd always better for outdoor indication?

Not necessarily. While a higher mcd may result in a brighter LED, it's important to balance brightness with viewing distance. Too much brightness can be uncomfortable for viewers, while too little may not be noticeable enough. It's important to consider the specific needs of your outdoor indication when choosing the correct LED mcd.

3. What is the recommended mcd for outdoor indication in different environments?

The recommended mcd for outdoor indication can vary depending on the environment. For example, LEDs used in direct sunlight may require a higher mcd rating to be visible, while those used in shaded areas may require a lower mcd. It's best to consult with a professional or conduct testing to determine the best mcd for your specific outdoor environment.

4. Can I use the same LED mcd for all outdoor indications?

No, the LED mcd needed for outdoor indications can vary depending on the specific needs of each indication. Factors like viewing distance, environment, and desired brightness all play a role in determining the correct mcd. It's important to carefully consider these factors when choosing the appropriate LED mcd for each outdoor indication.

5. Are there any other factors besides mcd that I should consider when choosing an LED for outdoor indication?

Yes, besides mcd, it's important to also consider the color temperature, viewing angle, and overall quality of the LED. The color temperature will determine the color of the light emitted, while the viewing angle will determine the coverage area of the LED. It's important to choose an LED with a high-quality construction to ensure durability and longevity in outdoor environments.

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