Before looking at the two different types, let’s first look at what LED filament is. Basically, it’s a load of LEDs laid out very closely together in a line so that when you apply power, it looks like the whole strip is glowing uniformly. If you turn the power down so that they’re only just lit, you can usually see the individual points of light, but as it gets brighter, these diminish, and shouldn’t be visible at full power.
LEDs can be hooked up in different ways. Basically, the power requirements of a strip come down to whether they’re hooked up in parallel or in series. Or, more commonly, there will be multiple blocks in parallel where each block is several strips hooked up in series.
As LEDs are semiconductors, they don’t obey Ohm’s law, and there are a couple of things you need to know about working with them. Firstly, there is a minimum amount of voltage they need to turn on. Secondly, if you apply much more than this, they very rapidly start to conduct too much current and can burn out. Typically, you prevent LEDs getting too much current with a protection resistor, but with high-output LEDs such as those in lamps, this can result in wasted energy. There are a few solutions to this, but the one that we’ve gone with is just to match the voltage to the LED strip closely. Now, let’s go back to looking at the different types of LED filament.
It’s got a few advantages of the flexible filament over the old type of ridged filament:
• It’s easy to bend into almost any shape you want
• 3 V supplies are plentiful and cheap
• It comes in 30 cm strands that give a pleasing effect without having to solder lots of strips together
Of course, there are some disadvantages:
• It’s not that bright, so if you want a lot of light, you’ll need a lot of strips
• Being low voltage, it’s a higher current for the same amount of light
The very simplified difference is that traditional LED filament is good for making light bulbs for lighting rooms. 3 V flexible LED filament is good for making dimmer, softer lighting that’s more akin to lamps.
Power and assembly
Each strip pulls about 120 mA when run at 3 V, and we needed a power supply. It would be easy enough to find one that can power this, but as this is an upcycling project, we decided to rummage through a box of old power supplies to see what we could find. We came across a 12 V 1 A supply that had formerly been some BT doohickey. 12 V is obviously a lot more than 3 V – in fact it’s four times more, so we wired four lengths of this LED filament in series. The electrics really were as simple as that.
Keeping with our upcycling theme, we scoured the kitchen and the wood-pile for additional bits and pieces. Four glass ramekins (that once held Gü puddings) served as the protection for the LED filament (sort of akin to the glass bulb on a normal light bulb), a bit of ply held the filaments and glass in place, and a larger chunk of wood acted as the base.
Assembly was just a case of drilling holes for the wires, hot-gluing the ramekins in place (OK, this should really have been done better – we’re going to excuse ourselves by calling this a prototype and improve it later, if we find it useful), and screwing the wood to the base.
There you have it. In total, the new parts we bought for this project were just four lengths of LED filament (about £1 each – search your favourite direct-from-China website, and you should find similar options). We also used a bit of hookup wire and solder to join it all together. Everything else was upcycled.
The flexible filament is easy to use, looks awesome, and is perfect for building your own lighting systems. We’d love to see what you create.
