Help me select 5mm LED's for SSD used in sunlight please

Hi guys, ive built a big SSD using 360 x 5mm LED’s. It has 4 digits including decimal points for each. i tested it out today and it was a total fail. The LED’s are so dim i cannot see them glow in the sunlight. i am powering them with 12v. each segment of the seven segment display contains 12 LED’s of which there are 3 parallel lines each containing 4 LED’s in series. each parallel line has a 100 ohm resister to limit current to approximately 20ma. i have included the spec sheet information in the picture attached.

My problem is that i do not understand how to select an LED according to how i want it to perform in my mind. The reason why i bought these were they had an mcd of 45 as shown in this link http://za.rs-online.com/web/p/visible-leds/6466642/

Now i had LED’s that had an mcd of 20 and they were bright so i thought an mcd of 45 would be brighter but they dimmer? so am i missing something?

can you guys also give me advice on what color and viewing angle would be best for daylight viewing? this is used for a motocross track timer and must be able to be viewed by riders in sunlight while riding. thanx for any help

calvingloster: Now I had LED's that had an mcd of 20 and they were bright so i thought an mcd of 45 would be brighter but they dimmer? so am i missing something?

You omit to mention what you are using to drive the LEDs, clearly not directly from the Arduino, and whether you have actually measured the current flowing with four in series and a 100 ohm resistor.

My impression - and particularly noting the red encapsulation - is that these LEDs to which you refer are positively antique - geriatric - in fact, obsolete! 45 millicandela is pitiful and 25 quite ridiculous. Do note the reference in Wikipedia which I thought I had better check before making too many derogatory comments about this.

(I mention the red encapsulation which was used to provide some contrast with the original variety of inefficient LEDs to permit them to be visible at all - I am embarrassed to have supplies of such LEDs here - the only purpose to which I can now imagine to put them is some sort of rough "Zener".)

Hi, are you multiplexing the display. If not can you measure the volts across the 100R resistor when it relevant LEDs are ON. That voltage divided by 100 will give you the actual current running through the LED. Also a circuit diagram of how you are switching the LEDs ON if you are using a transistor, BJT or FET.

Thanks, hope to help....Tom... :)

Paul__B:

calvingloster: Now I had LED's that had an mcd of 20 and they were bright so i thought an mcd of 45 would be brighter but they dimmer? so am i missing something?

You omit to mention what you are using to drive the LEDs, clearly not directly from the Arduino, and whether you have actually measured the current flowing with four in series and a 100 ohm resistor.

My impression - and particularly noting the red encapsulation - is that these LEDs to which you refer are positively antique - geriatric - in fact, obsolete! 45 millicandela is pitiful and 25 quite ridiculous. Do note the reference in Wikipedia which I thought I had better check before making too many derogatory comments about this.

(I mention the red encapsulation which was used to provide some contrast with the original variety of inefficient LEDs to permit them to be visible at all - I am embarrassed to have supplies of such LEDs here - the only purpose to which I can now imagine to put them is some sort of rough "Zener".)

Sorry I am multiplexing them from arduino using mosfets, (highside and low side switching) the brightness does not change much from being constantly powered from the battery or being multiplexed. What's funny about these led's that I forgot to mension is that the anode and cathode are switched around? Like normally the anode is the longer lead and has a flat spot on the plastic of the bulb. These LED's are opposite, the cathode has the longer lead and the indentation.

calvingloster: Sorry I am multiplexing them from arduino using mosfets, (highside and low side switching) the brightness does not change much from being constantly powered from the battery or being multiplexed.

Maybe not to your eyes in an indoor environment, but the measured actual light output will be much lower.

Why would you need to multiplex them? Presumably each segment has its own MOSFET, you can easily control that many MOSFETs from an Arduino using shift registers. This should be the first thing to try, before dismantling it: Change the software to light up one segment continuously, alternating with the same segment lit up multiplexed. Take it outside and see the difference between the two. If it's still not bright enough then you need different LEDs (although finding LEDs that can compete with the sun is a tall order).

PS: If you're going to rebuild it using different LEDs then I suggest using an6884 chips (or ka2284 which work identically) instead of MOSFETs/resistors. They simplify the wiring a lot for jobs like this. (Yes, they're "VU meter" chips but treat them just like a transistor with five current-controlled input legs...all you do is connect the Arduino pin to the input on them and they work great)

With 4 LEDs in series you could control up to 20 LEDs with each one of those. In your case you need one per segment instead of the resistors/MOSFET. Connect the control pins to the outputs of four shift registers, and... job done.

What power source you using?

(Not just usb power? :o)

fungus:

calvingloster: Sorry I am multiplexing them from arduino using mosfets, (highside and low side switching) the brightness does not change much from being constantly powered from the battery or being multiplexed.

Maybe not to your eyes in an indoor environment, but the measured actual light output will be much lower.

Why would you need to multiplex them? Presumably each segment has its own MOSFET, you can easily control that many MOSFETs from an Arduino using shift registers. This should be the first thing to try, before dismantling it: Change the software to light up one segment continuously, alternating with the same segment lit up multiplexed. Take it outside and see the difference between the two. If it's still not bright enough then you need different LEDs (although finding LEDs that can compete with the sun is a tall order).

PS: If you're going to rebuild it using different LEDs then I suggest using an6884 chips (or ka2284 which work identically) instead of MOSFETs/resistors. They simplify the wiring a lot for jobs like this. (Yes, they're "VU meter" chips but treat them just like a transistor with five current-controlled input legs...all you do is connect the Arduino pin to the input on them and they work great)

With 4 LEDs in series you could control up to 20 LEDs with each one of those. In your case you need one per segment instead of the resistors/MOSFET. Connect the control pins to the outputs of four shift registers, and... job done.

Thanx for your suggestion but I will stick to multiplexing because I want to make it work this way and that has been my plan since the beginning. Even if I power the led's constantly at 100% on all the time at 40mA they are too dim.

I have 10 LED's in my tool box that are rated at 20mcd and they are bright enough so they will work. I am just confused and that's the real reason why I started this post because the led's in the display have a 45 mcd rating so how can 20mcd be brighter than 45mcd. Obviously its not mcd that is the brightness or what?

calvingloster: I have 10 LED's in my tool box that are rated at 20mcd and they are bright enough so they will work. I am just confused and that's the real reason why I started this post because the led's in the display have a 45 mcd rating so how can 20mcd be brighter than 45mcd. Obviously its not mcd that is the brightness or what?

It's all about view angles. X amount of light spread over 180 degrees isn't the same as X amount of light spread over 30 degrees.

fungus:

calvingloster: I have 10 LED's in my tool box that are rated at 20mcd and they are bright enough so they will work. I am just confused and that's the real reason why I started this post because the led's in the display have a 45 mcd rating so how can 20mcd be brighter than 45mcd. Obviously its not mcd that is the brightness or what?

It's all about view angles. X amount of light spread over 180 degrees isn't the same as X amount of light spread over 30 degrees.

Well these two different LED's are both rated at 30 degrees of viewing angle so I don't think that's the problem

Well i have ordered 4500mcd 20degree viewing angle orange clear LED's. they were dirt cheep just hope the orange will be visible in the sunlight