Yes. That is, lower power, which is measured in W (Watts). The formula is W = V * A, so it is a product of both.

By lowering the voltage you lower the current, and the total power is reduced. Heat is proportional to power dissipation, and heat is what kills LEDs (and pretty much every other kind of component).



The area of LED power requirements can be confusing to a beginner, but don’t despair it is actually not very complicated. The reason for the difficulty is the nature of LEDs. They are non-linear devices, that is, their resistance changes with the current that passes through them. That’s why a separate current limiting resistor is required.

A plain LED will reduce in resistance, and so the amount of current it will try to draw, the more current you give it. You can see how this is a bad thing if the power supply can provide enough current to turn let out the magi smoke—the LED will commit self-harm in a moment.

With the correct current limiting resistor in place, there is a guarantee from an ohmic device that the current will not exceed the maximum the LED can handle. A resistor is ohmic because it doesn’t change resistance value based on the current passing through it¹. The LED is non-ohmic because it does. These designations refer to the relationship of each device to Ohm’s law. The ohmic device has a simple one, the non-ohmic device requires taking that changeability into account.

As far as the proper current goes (ultimately, we use the current at the devices forward bias voltage as the test for how much power we will be supplying) the best way to know is to find a datasheet for the device. In the absence of one, the general expectation is that an ordinary LED without a heatsink will be properly powered at 20mA. This doesn’t have to be correct but it is unlikely to be too much.

So, when you lowered the voltage you lowered the current the supplied current limiting resistor would permit to flow. At 10mA you are doing very well so far as longevity goes. If they are bright enough at that power level, that’s great. The goal is to run them as cool as you an while still having sufficient light output.



The strips I linked above are 5mm. I also misspoke a bit. I forgot that I found they had cut marks on them. When I recieved them I thought they didn’t, so cutting them would require finding the proper place through the phosphor, that’s not necessary. The only complication is that the cut marks are on the back, under the adhesive liner, to you have to peel it to find them. Not a fatal flaw, but a bit annoying.

Ahh so that's why I was only measuring 10ma over one led, I found that if I put a resistor of 10ohm before the strip that dropped a lot, but without much loss of brightness, but I then took it off as the resistor got so hot I couldn't touch it, so I binned that idea and came for some advice. Not sure how safe that resistor would have been, I tried a 100ohm resistor too which dropped the current even more but the lights were very dim with that added. I was just messing around trying to learn from mistakes. I may try those lights you linked in a future project as I do like that they dont show the single light sources, thank you

 

You wrote that your Li-Po battery is only 3.87V which is near half charged. Have you tried it powering the LEDs when it is fully charged at 4.2V? Or is the charger defective and charges to only 3.87V?

No I think the charger I connected is fine, got a bit hot but I literally only charged it for ten minutes, I only connected everything to test the LEDs and to try to figure things out. Once I fit everything I will give the battery a full charge and see what it's like with the boost converter connected. I don't like the idea of the lights getting dimmer as the battery drains, and then not lighting even though the battery still has charge in it, I prefer to keep a constant brightness even if I lose some time on the battery, dimmer lights wouldn't work well in there placement of the frame so I think it's the best option, but I guess I'll find out soon.

 

Why is everybody guessing about the resistors that are already on the LED strips and are clearly marked 121 which is 120 ohms??

The battery is not 3.7V. 3.7V is the selling and storage voltage that is about half of a full charge. Unless the LEDs are turned on for hairs then the battery voltage will always be near the 4.2V fully charged voltage.

 

I think the charger I connected is fine, got a bit hot but I literally only charged it for ten minutes, I only connected everything to test the LEDs and to try to figure things out.

The charger will not properly charge the battery when the battery is still powering the LEDs. Turn off the LEDs when charging the battery.

The Chinese charger might be poorly designed or defective if it gets too hot. Or maybe it is hot because it is wrongly trying to charge the battery plus light the LEDs.
Is the input voltage to the boost converter correct for it?
Is the output from the boost converter correct for the charger?

 

The charger will not properly charge the battery when the battery is still powering the LEDs. Turn off the LEDs when charging the battery.

The Chinese charger might be poorly designed or defective if it gets too hot. Or maybe it is hot because it is wrongly trying to charge the battery plus light the LEDs.
Is the input voltage to the boost converter correct for it?
Is the output from the boost converter correct for the charger?

Ive read that they do get hot while charging, and that they self regulate at a certain temp, but how true that is I don't know, the boost converter I bought can be changed to 5,8,9 and 12v output by removing or keeping a resistor, I didn't have that connected while charging tho, or the lights. I added those after a ten min charge just to see if it worked, sorry if I wasn't more clear. I plan to fit the charging board on a piece of 2mm aluminium to hopefully draw out the heat, that piece can be as big or small as is needed due to where I'm mounting it. I also have a little on off switch that will go on the back, so I'll make sure that the lights are turned off while charging. I had a thought that maybe because the usb plug I was using to charge the battery was 2.1amps and not 1amp, maybe causing it to get hot but I didn't check that yet. I think the r3 resistor on the charge board is set for 1amp but I'd have to look on the spec sheet to be sure. Cant see any numbers on that resistor as it's so small, I dont think I'd be capable of swapping that out anyway tbh

 

Why is everybody guessing about the resistors that are already on the LED strips and are clearly marked 121 which is 120 ohms??

I think you’ve mistake the strip that @Irving posted in https://forum.allaboutcircuits.com/...ith-an-led-project-please.190300/post-1777528 with the TS’ actual strip on which the resistors are all but unreadable though the appear to be labeled 101, so 100Ω.

 

I'm sorry to say that what I was trying to make didn't work out that well, it's a disappointment but I have an idea for something else, which if you guys could help with it would be much appreciated. I'll upload a couole quick pics I took of the pucture frame, but you will see that the light didn't work as planned, the 5mm strip of LED tape sits too far back by about 1.5mm so the light doesn't fill the picture fully, I don't like the look of it so I'm moving on from the idea.

 

What I'm hoping to replace it with is an outdoor solar light with a memorial type thing to go in her garden instead, using the same battery and components, mostly anyway, only I'm not too sure about how it would all work. I found a video on youtube of how to do it using an old phone battery but that has built in protection and the guy uses a diode, resistor and transistor to turn on the lights on and off, mine is slightly different as I want to use the charging board instead of the diode, I think it will work but once I've drawn the schematic I'll post it, hopefully you can tell me if it's safe, and if it will actually work.

 

I plan to use a 6v solar panel to charge the battery, but if someone could explain to me what size is best and why, that would be great, I really don't have the first idea of how the voltage of a solar panel effects the type of battery your trying to charge with it, I'm assuming its just a matter of how fast it can charge it but I'm just guessing.

 

Given that in the last sentence of the second paragraph in the initial post, the TS states that the LEDs are working, it seems that some of the guesses apply to other arrangements of LED strips. There are certainly many different arrangements possible, and with the strip being powered by five volts, and with the typical voltage of a white LED being at least 3 volts, it is safe to guess that each LED has it's own resistor already.
AND, given that the brightness is stated to be adequate, and that the question was about safety, I agree with Y in post #17, that the LEDs are being operated within their specifications, at a lower power, and thus will operate producing less heat and have a longer useful lifetime.
As for the battery voltage when charged, it will still be less than the five volt intended operation voltage, and so it will still be OK.
I do recommend that the TS measure the LED voltage when the battery is being charged, and if it is above five volts, to switch off the LEDs while the battery is being charged. Not for safety, but to prolong the LED useful lifetime.
I had not read beyond post #20 when I added my comment. Oh Well.

 

I think your problem is that the LEDs on the strip have a wide dispersion angle. To direct the light onto a single plane you would need a narrow angle. It would still be hard to get uniform illumination from the sides, though.

 

I have had some success in changing the illumination patterns by lightly sanding LEDs. And as there are more available some experimenting may produce adequate results. unused 400 grit paper works very quickly to alter the pattern. Not much force is required.

 

I think your problem is that the LEDs on the strip have a wide dispersion angle. To direct the light onto a single plane you would need a narrow angle. It would still be hard to get uniform illumination from the sides, though.

Could well be, but I think maybe it's due to the fact there is a gap between the brass angle and the picture which is 3mm, to allow the light out, the centre of the LEDs strip is 2.5mm so it hits the edge of the picture and doesn't fill the whole front, I have ordered a 3mm LED strip so that the centre of the light source will be exactly in the centre of the gap. I think that might fix it, but given that it looks good without the lights on I may just use it as a standard picture frame, just way more expensive than a wooden one lol. I'll probably make a new thread for the design of the solar light once I've decided how I want to do that.

 

Lithium is an extremely active metal like all other metals ending with "ium" (uranium, magnesium etc) and explodes or catches on fire when over-charged so a charger circuit designed for the battery must be used.
If you charge the 3.7V Lithium battery directly from a 6V solar panel then please post a video of the battery exploding.

 

Lithium is an extremely active metal like all other metals ending with "ium" (uranium, magnesium etc) and explodes or catches on fire when over-charged so a charger circuit designed for the battery must be used.
If you charge the 3.7V Lithium battery directly from a 6V solar panel then please post a video of the battery exploding.

I posted above, that I will use the same charge board I used in the frame, I just don't know what else I need, mainly to switch the lights on when the sun goes down. I think a little transistor will work in a dusk sensor style circuit, like I said I will draw out what I plan to use, for advice or rework