Which LEDs should I use ?

Thread Starter

ludesert

Joined Mar 6, 2022
4
Hello,

I'm currently designing a strobe light which will be mounted on a small aircraft to increase its visibility. The color of the flashe is red, and should be visible from 1-2 km if possible.
I made a first prototype and today, everything was ready, soldered, 3D printed ...etc. On the ground, the flash seemed quite powerful but for the test in flight, the intensity is quite deceiving.

I am currently using 5 CREE LEDs like this one : XBDRDO-00-0000-000000C01 (datasheet : here)
I am using Carclo 10410 lens (link)
The LEDs are driven by a MOSFET (no PWM, just some flashed controlled by a small board) with 0.8A flowing through the LEDs (they are mounted in series).

I am not a professional and this is the first time I deal with high brightness LEDs, and I guess I made the wrong choice. I saw lots of other items on CREE website but to be honnes, I'm lost.

I saw this kind of LEDs : https://cree-led.com/products/xlamp-leds-discrete/xlamp-xp-g3 but I don't know if they would be more or less visible since the luminous flux is indicated in mW and not in lumens as it is on the datasheed of the XBDRDO LEDs I used.

The only constraint is that I can't use huge LEDs, but if they are a bit bigger than what I use nt, it should be a problem.

I would be more than happy if you can help me in choosing the right components to reach my goal !

Thanks,

L.
 

MisterBill2

Joined Jan 23, 2018
18,176
I am presuming that the "small aircraft" is a mode, or a drone of some kind, not an actual airplane. There are indeed two sets of rues, rather different.
And the problem with flashers is that they al look brighter up close. Reflectors can hep, as can using the shortest possibe wavelength because that makes the light be in a wavelength of greater eye sensitivity.
That is whu actua Xenon fash tubes get used for strobes.
 

Thread Starter

ludesert

Joined Mar 6, 2022
4
Some of you guessed right, this is for a real aircraft; it will comply with EASA rules CS-SC032b.

I want to have red color because it will be more visible in certain flight conditions (eg: near clouds) ...
 

dl324

Joined Mar 30, 2015
16,846
Some of you guessed right, this is for a real aircraft; it will comply with EASA rules CS-SC032b.
You still need to have it certified before it will be legal. Certification for a homebrew light will be expensive. You'd be better off just buying something that's already certified.
 

Audioguru again

Joined Oct 21, 2019
6,674
Many young guys are replacing the lights on their cars with ebay cheap junk lights that are not certified because they are the wrong color, the wrong beam width and the wrong brightness. I think the police impound those cars.

Maybe airplanes also will be impounded if the lighting is modified and illegal.
I like seeing the lights on a Boeing Dreamliner taking off at night.
 

Thread Starter

ludesert

Joined Mar 6, 2022
4
Well ...Any advice for choosing the LEDs will be welcome. I don't want to create debate about certification rules which can be different depending on where your aircraft is registered.

Why did you choose that lens? How are the LEDs distributed? From where do you want visibility?
I forgot to mention that the goal is to increase visibility for opposite trafic si the strobe consists in 5 leds aiming in front of the aircraft.
 

Ya’akov

Joined Jan 27, 2019
9,071
Well ...Any advice for choosing the LEDs will be welcome. I don't want to create debate about certification rules which can be different depending on where your aircraft is registered.



I forgot to mention that the goal is to increase visibility for opposite trafic si the strobe consists in 5 leds aiming in front of the aircraft.
Why did you choose that lens? How are the LEDs distributed?
 

Thread Starter

ludesert

Joined Mar 6, 2022
4
Why did you choose that lens? How are the LEDs distributed?
The LEDs are distributed in a straight line aiming in front of the aircraft.
I whose that lens because of its compacity and the diffusion angle : concentrating the light in a 46x19° area seemed enough for me (there is no need for an opposite trafic to see the flash if it is too much on the left or right of my track).
 

Audioguru again

Joined Oct 21, 2019
6,674
Around here, airplanes that takeoff and land are all pointing into the wind in the same direction. Airplanes flying high are at very different altitudes and different locations so that they are not flying towards each other.
 

MisterBill2

Joined Jan 23, 2018
18,176
To be visible against the sun will take a whole lot of power for some incredible light intensity. So at this point I suggest working with one of the LED producing companies to see what they can provide.
The challenge with collision avoidance lights is the area that they need to cover. Straight ahead is not so hard, it is at an angle that the challenge is big.

Is there a commercially available product whose specifications you can find? That will provide information on what you may choose to copy. Knowing the requirements makes meeting them a lot easier.
Certainly following the standards for flight directions improves safety a lot.
 
Last edited:

Ya’akov

Joined Jan 27, 2019
9,071
The LEDs are distributed in a straight line aiming in front of the aircraft.
I whose that lens because of its compacity and the diffusion angle : concentrating the light in a 46x19° area seemed enough for me (there is no need for an opposite trafic to see the flash if it is too much on the left or right of my track).
So here's your problem. The lens you chose is giving you about 52° more or less. When you are close, that looks very bright, but the luminosity falls off by the inverse square law. That means that very rapidly what looked bright to you up close becomes a lot less bright.

For something as low powered as those LEDs, you will need more of them and a much narrower angle lens. They will have to be blinding up close to be bright enough to see at a distance. A very subjective test is to stand the same distance from commercial collision avoidance lights and compare the brightness. I believe you will find it a lot brighter.

That would be how bright your lights need to be, and with enough individual lamps that you can provide overlapping narrow beams the area you want to cover.

So it's not that the lens is too narrow, it's the opposite. You need an array of LEDs that can duplicate the normal collision avoidance light's luminosity at a given distance. One more way to look at it is that even if you can make your LEDs a bit more efficient, you can't gain that much efficiency, so a good benchmark is power consumption.

Check what commercial lights dissipate, you will have to be providing a similar amount of power to the LEDs to get similar results. It won't be as much, but depending on the technology of the other lights, you will need to be providing 50% or more of the power (at a rough guess).

I think you can make it work, but I think you need to narrow the beams and up the device count to do it.
 

MisterBill2

Joined Jan 23, 2018
18,176
Easier than checking commercial lights, check the FAA requirements for beamwidth and intensity that are published. Then there will be no guessing required.
For small drones the choices are simpler.
 

Ya’akov

Joined Jan 27, 2019
9,071
I wonder about the permissibility of using lasers in this application, particularly up close. But it is a good idea. There are laser headlights, though they use a blue laser with a phosphor target and reflector optics.
 

ericgibbs

Joined Jan 29, 2010
18,766
hi,
The Rules about lasers are quite clear and no big deal or burden, if they are correctly understood.
I designed/manufactured and sold worldwide laser ranging devices for over 20 years.

E
 

MisterBill2

Joined Jan 23, 2018
18,176
Clearly rues being "quite clear" is not the problem, nor even correctly understanding those rules.
The problem for some applications is complying with those rules, and then being able to PROVE that they are being complied with, to those demanding the proof.
Your experience may differ.
 
Top