I'm new to electronics, and I feel like this is a really basic question but I can't find any answers anywhere. So, how do you determine the brightness of LEDs, more specificially, I want to build an LED strobe for my car, bright enough to be seen during the day, think police strobe. I tried converting the mcd and angles from LED specs to lumens since I can compare lumens to various flashlights I have, but that's not getting me anywhere... Unless it wont work, I was going to use this design http://danyk.cz/ledstr_en.html to make the LEDs strobe, only because I also want to build a lower powered strobe that this should work fine for.

 

Photometry is a complex subject, you are not likely to arrive at what you need by comparing specs.

Buy and test some LED's. So much depends on the ambient lighting conditions.

You will always have to deal with trade-offs like beam angle trading for perceived brightness, etc.

 

Crap, was afraid of that lol, happen to have any starting point choices? I was going to place an order from Allied Electronics. I intend to build a reflective shield to back the LEDs and focus the light more forward if that helps.

 

You need to consider all the variables- then range-in on some potential parts.

LED color?
Power Level?
Beam angle?
SMD / Thru Hole?
Cost?

Start with these.

 

One thing that might help is to look at the specs for luminous efficiency, the total light produced compared to the energy consumed. This slowly increases as technology advances. A top supplier like Cree will provide that sort of information. The cheapo LEDs from China will not and you can pretty well assume those are a few years or more behind. After that it’s all about reflectors and angles and lenses.

 

Blue
Not particular to SMD vs Thru hole, I suppose thru hole if there's a choice.
Cost, I'd obviously like cheaper, but I need it to do its job so Ill suffer here

Power and Angle are the parts I'm getting caught on, I pulled up a MCD/angle conversion to lumens since I understand lumens better, but every led I calculated resulted in close to 1 lumen, way too low and averall not a helpful conversion since all the LEDs I calculated ended up close to the same...

I'm trying to build a forward facing blue strobe for my car, it'll be interior, and ill be building a housing to prevent blowback, the most important quality I need is for the light to be bright enough to see in the daytime.

 

You can get up to about a 1 watt blue LEDs in a thru hole style 10mm clear, but above that you will need to go to the SMD style. 1 to 5 watt mounted on the “star” spreader, 10 watt and up in the “square” style.

The square style SMD LEDs (COB) are pretty easy to mount compared to the star style, but they are also a higher voltage.

Yes, the type I am referring to are from China, they pretty much hold the niche for DIY, and cost much much less than something from Cree…the thing is…you just have to know who you are buying from…there are not a whole lot of companies that actually make the chips, but there are a ton of companies that produce the finished product.

 

How much higher? It using a car system so 12v, I'm looking to make 2 units roughly 5-7" long, thin as possible but anything under 2" should be workable. Any idea if the original circuit I posted will work with LED that size?

 

Yes something like this should do the trick @ 12 volts using a single dropping resistor. (or whatever driver circuit you want)

https://www.ebay.com/itm/High-Power...1c:m:mVlFbKnDXx1iSQmZVbt5fJQ&var=511479217126

The 10 watt version.

 

Sorry, but what do you mean by driver circuit and single dropping resistor or are you referring to the link i posted? Ill try those LEDs! Thanks!

 

The design you linked to is a joke ... No power ... each led is 30mA ! ... 0.1W x 36 = 3 W total power

LEDs are awesome for strobes ... very easy to build one cheaply with many 10's of KWs

I suggest you use this as your basic led chip

100W 32v 3A ... about 5cmx5cm ... only a few $ on ebay .... 10 of these will make a good strobe, that can run from a car battery.

Just one of these 100W chips will put out 30 times more light than all the 36 small leds in your link

 

think police strobe

A strobe light which could be confused with a police one would be illegal in some (at least) jurisdictions. Which country are you in?

I intend to build a reflective shield to back the LEDs and focus the light more forward if that helps.

I don't see how it would. Unlike incandescent bulbs, LEDs don't emit light to the rear.

 

@oz93666…how can you run a 32 volt COB with a car battery? I mean without a booster module.

As to driving the 10 watt COBs:

I would place several in a cluster and select a resistor that would drive each one at around 400mA @ the center of the voltage range. (one resistor per COB)

This gives you plenty of headway, and be sure to use a proper heat sink. (heat sink and proper derating is the key here)

Also, be sure to use the proper wattage resistors.

EDIT:

O yea I forgot…a proper high power MOSFET is also needed, probably with a heat sink as well.

 

Thank you all for the input, but it would seem that I just don't have the understanding to do this... I understand what everyone is saying just no idea how to really implement it. As for the legality question, I'm in the US, I'm an EMT, and we have permits to use blue strobes to aid us in getting through traffic, I just thought I could build a strobe cheaper than the ones available and more form fitting to my particular vehicle.

 

Thank you all for the input, but it would seem that I just don't have the understanding to do this...

That doesn't stop a lot of the folks that come here!.

I understand what everyone is saying just no idea how to really implement it.

This is a doable project even for a first timer, but like so many first projects, they don't always end up meeting expectations the first time through. I think if you want to pursue this, you should plan to do some experimentation. Check out a few LEDs, try out the flashing circuit, and so on. Start small so that you can collect enough data (and confidence) to tackle the final build. There are plenty of folks around here more than happy to help you at each step.

... I just thought I could build a strobe cheaper than the ones available and more form fitting to my particular vehicle.

Since a flashing blue strobe is a thing you can buy, it's unlikely you can put one together for less, especially if you need to buy a few tools (soldering iron and solder, multimeter, parts, wire, enclosure, connectors, etc.) to get it built. If nothing on the market suits your needs, only then would it be "worth it" to build your own. If you like the challenge of a project and learning new things, then charge ahead. Just don't expect to save money.

 

Ill keep at it, don't worry, I just feel that of the lights available to purchase, I'm paying for things I don't need.
For instance:

https://www.strobesnmore.com/Strobes-N-More-D12-Synchronizable-DashDeck-Light.html

22 patterns, unneeded, this is a 12 led strobe. With the circuit I linked and the 10 watt LEDs linked before, assuming they worked together as is, cost $50 in components, a sheet of acrylic for the housing is about $6 more for the size needed. Home made, I can fabricate 2 lights for the price of this one, and that's not taking into account that this particular light is twice as long as what I want, however most of the lights on the same site that are half as long are more expensive!

Basically, I wanted to make them simply because I can build to my specs for far cheaper.

 

Do remember that you are going to be creating a lot of heat and your housing is going to have to tolerate it. Acrylic may not be a good choice if you are going to make this very compact.

 

Gotcha, space wise behind the LEDs, I have plenty of room, its just thickness and length I want to restrict. Heat management was the next thing I was going to research for this project.

 

Several LED makers have application circuits on their websites and you can learn a lot from them. And the education is free.

 

Gotcha, space wise behind the LEDs, I have plenty of room, its just thickness and length I want to restrict. Heat management was the next thing I was going to research for this project.

It may not seem like it but you can take for granted that the electronics part of this project is relatively easy. The mechanical build, with attention to heat sinking, is the bigger challenge. Not rocket science, just challenging. Once you know what LEDs you want and what you want them to do, the electronics will be a snap.