UNUSUAL APPLICATION LED

[hotrod]

Would welcome opinions on T-1 3/4 (5mm)white led application. Use for backup lights for street rod car. Four would be mounted each side of license plate, each angled horizontally with slight overlapping pattern. Each 13,000 mcd, viewing angle (2xTheta) of 15 degrees.
1. Will it be bright enough?
2. Can tip be sanded and polished fo a larger viewing angle? (30 degrees)
3.How do you calculate the proper resistor to use on a 12V system? Led voltage rating 3.3V, current 30mA.
4.What would the approximate mcd for a water clear led to be seen in daylight in car dash?
Thanks in advance
Hotrod​

 

[Illum]

1. depends on your personal preferences
2. yes, though the exact angle in addition cannot be determined until more detail is given, the more you sand the dome off the wider the viewing angle can be attained
3. go to here: http://led.linear1.org/led.wiz

• Note that to prevent 5mms from prematurely burning out its best to restrict the current applied to each LED to around ~25ma
• So you'd input: Source voltage [13.8], LED forward voltage [3.6V or as specified on your LED pkg], LED forward current (ma) [25], then specify quantity of LED to be used on the 4th box
• Once you determine a figure, say 7.6 ohms but where you are you cannot find an existing resistor in your resistor bank that matches it.
• use http://www.1728.com/resistrs.htm to determine which resistors you have can be parallel to reach the determined value, in this case 7.6 ohm can be attained by using a 10 ohm and a 33 ohm in parallel

4. IIRC mcd is calculated using integrated equipment and cannot be determined by given information.

• While there are calculations that gives an approximate ball park value I have no idea how the calculations work so I can't help you on that

 

[JohnR66]

Probably bright enough to be seen but not to see with them. Unless used in conjuction with the regular backup lights cars have, you might confuse the driving public as to their purpose.

Reverse indicators are typically used for a few seconds at a time, so 30ma in 5mm LED should not be a problem. If they are cheap ebay LEDs (many rated 13,000 mcd) beware. Most fade fast and can outright fail. Get good performing LEDs. Flux LEDs are a better choice IMO. Putting 3 in a series with a 150 Ohom resistor gives around 27ma depending on the actual voltage while the engine is runing and Vf of LEDs.

You could do two rows of three on each side.

Do this at your own risk. May not be street legal.

 

[PCC]

2) I've frosted a JELED that has a 15 degree projection angle and this changed the light pattern to just about 270 degrees. Where the hotspot was is now a slightly brighter spot than the rest of the output. I did not take any excess material off the dome, just roughened it up.

3) When I bought my JELEDs they threw in a bunch of 510 ohm resistors to use these LEDs in an automotive application. This should give you just under 19ma of current. Dropping to 400 ohm resistors gives you just under 25ma. This is based on a 13.2V system, which most car electrical systems are at with the engine running.

 

[hank]

Remember you can get significant voltage spikes in an auto system especially when starting up. I use aftermarket LEDs in vehicle dome and seat lights, but I'm careful not to have them switched on when when I start the engine.

Someone here will know what to recommend.

This might be a place to look, search "automotive": http://www.ledsupply.com/