LED selection for application similar to an emergency vehicle light (Class 1)

[doublec4]

Hi all,

New to the forum here after doing some internet searches regarding LED selection. Looks like there are a lot of LED enthusiasts on here that might be able to help me out.

I'm in the process of designing and building an LED beacon of sorts. I started my design using some Whelen Mini Ion light heads, but my application is battery powered and these lights are potentially not as efficient as they can be. I'd like to take a crack at designing my own light, hopefully of similar brightness but more efficient if possible...

I've posted this thread over on the EEVblogs forums that goes more into depth about the beacon.

Some friendly people pointed out that the Whelen light heads are likely employing some kind of linear current regulation and could potentially be made more efficient using a switch mode current regulator. The Whelen website for the light heads does not list any specs on the lights other than the single color units conforming to SAE Class 1 for emergency vehicles. A quick google search and I found this info:

SAE Class 1 Warning Lights are most often used for emergency response vehicles such as police, fire and ambulance. Lights in this class have a candela value greater than 8100, with some reaching close to 18,000 cd-s/m when used to clear traffic in emergencies. SAE Class 1 lights are 4 times more intense than SAE Class 2 lights and 10 times more intense than SAE Class 3 lights.

Whelen light head has 6 LEDs in them (about 1.75mm x 1.75mm x 1.5mm tall)... I'm new to a lot of this terminology and concepts behind LEDs, so I'm not sure how the candela system works... for example the 8100 value just gets divided by 6 LEDs to find the individual candela rating? I have a feeling this is not the case... something perhaps someone can explain and I will also look it up.

What I would like to reach out and ask is... if I were to design my own PCB to fit inside of the Whelen light footprint, what small SMD LED packages (perhaps 4mm x 4mm or smaller without built in optics as the Whelen lens would take care of increasing the viewing angle) would people on this forum recommend for both brightness and efficiency? I have to create three different light heads. One is solid amber, another is solid white, and another would be a dual color Amber / Red. The dual color would still use only the same number of LEDs as the single color units. For example, if the single color units used 6 LEDs, the dual color would be 3 amber and 3 red. Overall brightness would obviously drop but I can accept this due to limitation of packaging.

Thank you!

 

[scout24]

Hello there and welcome! I approved your post without the off-board link.

 

[doublec4]

Hello there and welcome! I approved your post without the off-board link.

Thanks scout24, is it possible to somehow link to that discussion? I understand I'm a new member so if not, I can sort of copy and paste some of what was said over there. I just didn't want to duplicate things and waste anyone's time.

Thanks!

 

[Dave_H]

Does "battery" mean automotive battery, or self-contained i.e. Lithium-ion etc.?

My interest is using "auxiliary" automotive LED lights. Many run from 10-30v dc using switching dc-dc down-converters which drive white LEDs at constant current up to 1A or more (3W). From 12v it's easy to drive three white LEDs in series (9-10v typically). You could also drive red or yellow/amber similarly. Drive current is settable by a single resistor.You can even dim them with analog voltage 0-5v, or PWM (duty cycle) input. With some additional digital logic, you can provide flashing/strobing; depends how fancy you want to be.

Have a look at PT4115E driver chip as example. There are several other common ones out there. It's a very small device and runs up to 90% or higher efficiency.

Linear constant-current regulation is likely to have lower efficiency, but not always the case, depending on supply voltage and how the LEDs are wired.


Dave

 

[Dave_H]

BTW OP may find some useful discussion on this topic in the Transportation/Automotive
and Special Application forums, as what you are doing relates to devices themselves and
the application.

https://www.candlepowerforums.com/vb/showthread.php?378102-Road-Flare-alternatives

Perhaps you can advise what type of flashing you are looking for. It could range from simple
on/off coming from a cheap generic IC, to more complex patterns from a custom circuit
i.e. micro-controller (which you could develop if so inclined) or buy OTS. Some sort of prefab
modules likely exist.

Dave