I want to build a LED flood light board use 3.3 volts or 5 volts (White color LEDs)

[sam_sam_sam]

Which voltage would be better to use and why
If I use a 5 volt switching power supply what value resistance should I use

I going use a 8” diameter circle circuit board (that I am going to cut out ) I want to fill it with as many LEDs as I can t5 or t10 size LEDs

[mariushm]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

5v leds? those are probably led strips, which would come with resistors for every led or for every r,g,b of the led or the current limiting is built in if you're talking about programmable RGB leds set to white.

You should focus on the CRI rating of the leds (you want as high as you can afford) and the color temperature (CCT) , voltage should be the last thing that matters.

CRI is important for good color reproduction (85 would be acceptable, at least 88 would be recommended for photography or videos etc) , and color temperature also matters...
As for color temperature, maybe between 2700k and 5000k ... ex 2700k = warm white , 3000k soft white, 4100k = cool white, 5000k daylight

I'd suggest going with surface mounted leds since they'd be easier to solder on wide copper pads which would radiate heat away so they'd stay cooler.

Here's some suggestions : (85+ CRI, any CCT) : https://www.digikey.com/short/jz1wff

For warm white these look nice: https://www.digikey.com/product-deta...9-1-ND/5765360


Filter further by viewing angle (you'd probably want 90 degrees or higher to have light spread more evenly if you want light board) and then by current per price and package that's easier for you to solder.

If you want just something to light up some space where you're not gonna do photography or shoot videos in (basically have lightning like fluorescent bulbs) you can use leds with CRI less than 85



Ideally you'd use a led driver, not a resistor to limit the current.

White LEDs have a forward voltage of around 3.2v so if you use a 5v power supply you're gonna drop a lot of voltage on the resistor, seems like a bad choice.
You'd be better off having series of 3 leds or 5 leds and run them from 12v or 18.5-19v

Figure out the current you want your leds to light at and then you simply have the formula V = I x R to work with.

So if you have a single LED and 5v power supply and you want 20mA, then :

Vin - Vled = I x R so R = ( Vin - Vled ) / I = (5 - 3.2) / 0.02 = 1.8/0.02 = 90 ohm ...

... so if you want you can round it up for slightly less current.

but this way, you'd need one resistor for each led and that's silly.

You can put several leds in parallel and use only one resistor, but some leds will have slightly lower forward voltage, some higher forward voltage, they may not all be equally bright, and some may burn out and if that happens, the current goes up for all leds.

So for example you can put 10 leds in parallel and if they're rated for 20mA each, then maybe for safety go with 18mA per LED and you'll have 180mA of current:

R = (5v - 3.2v) / 0.18A = 10 ohm

and the resistor must be rated for 0.18 x 0.18 x 10 = 0.324, so at least 0.5w but i'd use 1w resistor.

Then, when one led burns out, you have 9 leds with same 180mA going through, so each of the 9 in theory gets 20mA going through it, still OK. If one more dies, you have 8 leds and 180 mA or 22.5mA .. and from that point all leds could die out one after another.

That's why you don't see parallel leds often, it's easier to have series of leds and use either higher input voltage or a boost led driver, which raises the voltage as much as needed to hit the sum of the forward voltages for all leds.

If you go with 12v and 3 leds in series but keep current at 20mA then :

R = (Vin - 3 x Vled) / I = (12-3x3.2) / I = 2.4 / 0.02 = 120 ohm

You'll also have to determine the power rating of the resistor, which will be P = IxIxR = 0.02 x 0.02 x 120 = 0.048 watts in the case of 120ohm and 20mA, so you'll need to use at least a resistor rated for 0.1 watts.

[sam_sam_sam]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

For warm white these look nice: https://www.digikey.com/product-deta...9-1-ND/5765360


Filter further by viewing angle (you'd probably want 90 degrees or higher to have light spread more evenly if you want light board) and then by current per price and package that's easier for you to solder.

Figure out the current you want your leds to light at and then you simply have the formula V = I x R to work with.

So if you have a single LED and 5v power supply and you want 20mA, *********
********but this way, you'd need one resistor for each led and that's silly******

So for example you can put 10 leds in parallel and if they're rated for 20mA each, then maybe for safety go with 18mA per LED and you'll have 180mA of current:

R = (5v - 3.2v) / 0.18A = 10 ohm

and the resistor must be rated for 0.18 x 0.18 x 10 = 0.324, so at least 0.5w but i'd use 1w resistor.

Thanks for this link I found the ones I want to use for this project

The reason I want to 3 v or a 5 volt power supply the 5 volt ones I have a lot of them that I bought surplus and want use them

https://www.digikey.com/scripts/DkSe...99982441957669

[redwire]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

Since each LED is around 3.4V, a 5V power supply is not good. 1.6V is wasted as heat in a resistor. A 12V supply with three LED's in series, wastes 1.8V on a resistor as heat, but for three LEDs, not one. I like higher voltage with strings in series.

Did you mean 5mm or 10mm through-hole LED? (T10 is a wedge base for 194 car lamps). These epoxy LED's are low power, 20mA usually.

So I think it's better to use fewer high power LED's, unless you want to solder 300 LEDs...

I use 1W or 3W SMT "bead" LED's (very cheap) and each is at least 10X-20X more power than a T1-3/4 5mm LED. Then getting rid of heat becomes the challenge. They have a thermal pad on the back, mounted to aluminum PCB.
So you need 10-20X fewer LEDs for the same light output. People tell me COB LED boards are better but I have not tried them.

Or you can buy a single very high power LED, like a 50W LED and use that. I found the quality of light poor, shadows, fan-cooled, not good for the workbench.

[sam_sam_sam]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

******* want to solder 300 LEDs...
Then getting rid of heat becomes the challenge. People tell me COB LED boards are better but I have not tried them.
T1-3/4 5mm LED.

Which ones are the 10mm LEDs

I might use the COB LEDs if can find a good price on them

The reason I do not want to use high power LEDs is because I do not have deal with the heat or heat sinks on this board

I think I am going to use a five volt switching power supply with a LM317 set to the current that I need to use for the amount of LEDs that I have on the board

I have some of these what I call a flood light it has 10 LEDs on a board and it pretty bright light with a 3.1 volt switching power supply powering it
It has been running this way for about 4 years

These LEDs flood lights were solar powered LEDs lights but the batteries and battery board did not work as well as I thought it should so I hacked them

[Curious.George]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

The reason I want to 3 v or a 5 volt power supply the 5 volt ones I have a lot of them that I bought surplus and want use them

https://www.digikey.com/scripts/DkSe...99982441957669

Depending on how you define "a lot", consider, instead, making a "rolling (marquis) display" sign -- for home or the rear window of your vehicle. I've got a 7x105 array of bicolors.

Note that the total power is less as you're multiplexing the display so they aren't all (potentially) "on" at once.

It's also a great little programming project (if you're into that sort of thing).

Amusing thought exercise: why do the letters on marquis displays "slant" (tilt?) while in motion?

[Curious.George]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

I think I am going to use a five volt switching power supply with a LM317 set to the current that I need to use for the amount of LEDs that I have on the board

A 317 will only give you ONE current source. So, you'd need to string all of your LEDs in series in order to just need that one. If you do so, the 5V won't give you enough voltage compliance to drive the string.

Also, note that the 317 is a regulator -- even when configured as a current source. So, you don't need a regulated supply to drive it. (OTOH, you will have to consider Pd in the '317 regardless of the input voltage)

[mariushm]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

Your Digikey link in reply to my previous post doesn't work, so I'm not sure what product you're referring to.

-

My advice would be to stop thinking about how to power your leds with 5v or lower.

Yes, you can use your 5v power supply but my advice would be to create one or several strands of leds in series and then power them from a higher voltage.
You can use a led driver board or a boost regulator to raise your 5v to a reasonable voltage.

For example, have 4 or 5 white leds with a forward voltage of 5 x ~3.2v = ~ 16v and then you can power your led driver board or boost dc-dc converter with 5v.. 12v and boost the voltage to around 15.5v .. 16v .... and use a single resistor on each strand of leds to limit the current.

eBay has loads of such boost regulators (boost is another term for step-up, a regulator that raises input voltage) : https://www.ebay.com/itm/DC-DC-USB-2...e/272682265912

These ones are pre-configured for 12v output, but you can adjust that by simply replacing one of the 3 resistors on the board with another value : https://www.ebay.com/itm/DC-3-3V-3-7...r/201919379310

You can also find these on amazon.com if you don't want to wait a lot of time for stuff to come from Asia.

You can make your own boost regulators using very cheap regulator ICs like *34063 or *33063 and you have calculator software - https://sourceforge.net/projects/mc34063uc/ - which computes all the values for parts you need and you can order all those parts from stores like Digikey, but when you add them up they may cost 2-3x more than those eBay boards.

[redwire]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

Which ones are the 10mm LEDs

I might use the COB LEDs if can find a good price on them

The reason I do not want to use high power LEDs is because I do not have deal with the heat or heat sinks on this board

I think I am going to use a five volt switching power supply with a LM317 set to the current that I need to use for the amount of LEDs that I have on the board

I have some of these what I call a flood light it has 10 LEDs on a board and it pretty bright light with a 3.1 volt switching power supply powering it
It has been running this way for about 4 years

These LEDs flood lights were solar powered LEDs lights but the batteries and battery board did not work as well as I thought it should so I hacked them

You can run high power LED's (say 1W or 3W) at lower currents, to not need heatsinks. They are more efficient too. Run them at say one-tenth power 0.3W

5VDC PSU and 90R 1/4W resistor for 20mA (0.064W/LED) or 18R 1/2W for 100mA (0.32W per LED), as examples. A resistor works fine, LM317 is not needed.

My point is one large LED can do the work of five little ones.

Here are through-hole LED pics, T-1 3mm and T1-3/4 5mm are most common, the 10mm is the same LED die and just more lens. Same light output just different lens.

[sam_sam_sam]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

You can run high power LED's (say 1W or 3W) at lower currents, to not need heatsinks. They are more efficient too. Run them at say one-tenth power 0.3W

That is food for though

Thanks

[sam_sam_sam]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

Here is the link to where I bought the LEDs that
I am going to give these a try I bought 25 of them

https://www.digikey.com/product-deta...JyZlZtMm5FZiJ9

[budm]

Re: I want to build a LED flood light board use 3.3 volts or 5 volts (White color LE

Do you have COSTCO card?
They have 2-pack on sale for $4.89
Buy them and take them apart to see if you can modify it to what you need.