Which kind of LED should I use for a lamp?

Question

I'm trying to make a cheap DIY LED nightstand Lamp.

I'm looking for recommendation on which kind of LED I should use to make enough light to call it a "lamp".

Ideally I would use a 9V battery to power the system. Since the whole thing is for a workshop with multiple kids doing multiple lamps.

I've looked around on Digikey and didn't find any SMD or TH LED that will do the trick for me.

I bought a few of these.

But the soldering is too hard for kids, and with the small test I made the light emission seems really low.

Any idea on what I could use?

Answer 1

Here is something a bit more modest in ambition. I've taken two pieces of swag, a 5V USB power bank (bearing genuine FCC and UL markings) that probably contains a single 18650 battery (in a metal case). It has a micro-USB charging port. The case is about 20mm x 20mm x 95mm. A 'free gift' from a seminar.

Paired with that is a directional reading lamp (a giveaway from Microchip) which contains 6 bright LEDs. As you can see the light is nothing like the total output of a 60W incandescent bulb, but it is extremely useful, and is just as bright from a close distance. I suspect the light contains only resistors and LEDs. The optical diffuser works quite well.

The problem with 9V batteries is that they contain very little energy, and are also very expensive per kWh. A rechargeable Li-Ion battery pack solves both those problems (the power bank supplies 5V regulated at up to 1A and is rated at almost 8Wh). A commercial 60W-equivalent LED bulb consumes about 12W which is far more than the unit can supply, and if it could supply it, it would work for just a short time. The reading lamp only draws 130mA, or about 22mA/LED.

So your project could consist of 6 LEDs, 6 resistors and a USB cord, plus maybe 3D print a housing. The one shown appears to be an overmold over a gooseneck kind of things so it holds position. There are ways to do that.

At the 15-25mA level you can just pick the brightest 5mm LED you can find (or afford) and use a number of them. Spacing them out so that they don't overheat is part of the design.

Answer 2

If you want a usable lamp on batteries, you'll need a high Lumen per Watt LED which gives the best battery life versus light flux compromise, and also a pleasant color temperature (ie, warm white, not cool white).

All the good lighting LEDs that fit the bill are surface mount only, which is going to be a problem if you want kids to solder them in a workshop... unless you buy pre-assembled PCBs or MCPCBs or strips with the LEDs already soldered.

I think the best would be to use flexible LED strips. They are easy to find online, and the kids should be able to solder them easily, it's just two wires. The strips can be cut to length according to your lamp design (check on the documentation where it can be cut).

Since these strips will use resistors to set the current, this isn't the most efficient solution, but it is a good compromise vs ease of building.

If the strip takes a 5V supply, the easiest is to power it from a cheap cellphone charger. You can also use 4 AA rechargeable batteries, the light will slowly dim as the batteries discharge, but that shouldn't be a problem.

Forget about the 9V battery. These are only for low current applications, also they are extremely expensive.

Another option would be to use some hig-power LEDs, which you would buy on star MCPCBs, but you will need a switching driver. These aren't expensive, but it's still an extra part. You can try aliexpress or banggood, there are tons of options.

Answer 3

The CoB LED you tried is only 117 lm/W.

If you search Digikey Optoelectronics > LED Lighting - White and sort by Lumens/Watt you will find an LED that does 229 lm/W. Everlight 62-227ET/KK7D-3M5050X6Y62629U6/2T/EU

A 9V battery is insufficient for a bright (60W equivalent i.e. 800 lumens) LED lamp. A 9V alkaline has about 550 mAH which would last less than 1 hour driving 229 lm/W LEDs with at the brightness of a 60 Watt light bulb.

If you want a warmer LED the 3500K 80 CRI LED is 213 lm/W.

The 229 lm LED has an output flux of 40 lumens @ 65mA and a forward voltage of 2.75v. You do not want to run these at a higher current as the extra heat will decrease the brightness 10-20%.

For 800 lumens each lamp will need 20 LEDs and 1.2 Amp @ 2.75v, 600 mA @ 5.5v or 400 mA @ 8.25V.

You mentioned you were looking for SMD LEDs. Later you say soldering is difficult. What you may rather use is an 8.8V Samsung Strip at $12. At 550 mA it will give you 800 lumens.

Or a better option might be a $4 Bridgelux EB Series Gen 2 Strip powered by a $7 Mean Well LDB-300L Constant current Boost LED driver with a 9V input and 300 mA output which would give you ≈1000 lumens at the 300mA output of the LDB-300L driver.

Then an issue with battery powered LEDs is the brightness decreases as the voltage drops. It is recommended at constant current regulator be used which is the equivalent of a variable resistor that auto-adjusts the current to whatever voltage. I would recommend the ON-Semi NSI45060JDT4G .

For batteries I'd go with a 9.6V NiMH rechargeable battery pack (8 AA) which is good for about 600 recharges when discharged to 50% per charge.