Modelling fluorescent strip lights (7mm scale) - LED filament bulbs

[Mol_PMB]

I'm working on a few model building projects at present, which feature external lighting by fluorescent strip lights. I'm interested in ideas for recreating this type of light in 7mm scale - so perhaps a light source that's about 20mm long and 1-2mm wide.

 

Here's one example where the light is bracketed from a building:

 

Here's another example where it just seems to be an internal-type striplight hanging under the eaves (not very clear, I confess):

And then there are some freestanding streetlight types in the goods yard:

 

I'm wondering whether to try 'LED filaments' as used in clusters in some domestic full-size light bulbs, but also available individually on ebay in various sizes and colours, for example:

https://www.ebay.co.uk/itm/266482506145

 

I expect they would be far too bright at their rated current though, and I think some of these modern-type LEDs don't respond so well to lower current (i.e. they're either off or too bright).

 

I was wondering if anyone had experience of using these 'LED filaments', or ideas for other alternatives?

Any thoughts welcome.

 

Cheers,

Mol

[Paul H Vigor]

1 hour ago, Mol_PMB said:

I'm working on a few model building projects at present, which feature external lighting by fluorescent strip lights. I'm interested in ideas for recreating this type of light in 7mm scale - so perhaps a light source that's about 20mm long and 1-2mm wide.

 

Here's one example where the light is bracketed from a building:

 

Here's another example where it just seems to be an internal-type striplight hanging under the eaves (not very clear, I confess):

And then there are some freestanding streetlight types in the goods yard:

 

I'm wondering whether to try 'LED filaments' as used in clusters in some domestic full-size light bulbs, but also available individually on ebay in various sizes and colours, for example:

https://www.ebay.co.uk/itm/266482506145

 

I expect they would be far too bright at their rated current though, and I think some of these modern-type LEDs don't respond so well to lower current (i.e. they're either off or too bright).

 

I was wondering if anyone had experience of using these 'LED filaments', or ideas for other alternatives?

Any thoughts welcome.

 

Cheers,

Mol

https://www.ebay.co.uk/itm/404490862643?chn=ps&_ul=GB&var=674460254210&_trkparms=ispr%3D1&amdata=enc%3A1MT1oylFuTIKxNXuL1j3ZNw36&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&mkscid=101&itemid=674460254210_404490862643&targetid=2338077059482&device=c&mktype=pla&googleloc=9045392&poi=&campaignid=17206177401&mkgroupid=165034047246&rlsatarget=aud-1657461039788:pla-2338077059482&abcId=9300866&merchantid=6995734&gad_source=1&gclid=CjwKCAjw59q2BhBOEiwAKc0ijUfDQCYEoN87k5QGDwtOzLgmaZDrsV_reHbxGVXSHgm1xJdIsLwbbhoCag0QAvD_BwE

 

Google produced this. 3v. Any good?

Edited September 3, 2024 by Paul H Vigor
to add information

[Mol_PMB]

Yes, I think this kind of thing is the way forward. They seem to exist in various colours and lengths, though short ones (less than an inch) are hard to find.

Effectively they're a by-product of the domestic LED lamp industry, and so a relatively recent development.

I'll order a few and report back here.

The longer flexible ones might even do a neon sign.

[Mol_PMB]

Another possible alternative is something like this strip:

https://www.ebay.co.uk/itm/374189763144

https://www.ebay.co.uk/itm/375093365342

 

Which is good for applications under canopies, as one of my local friends has just reminded me, seen here in HO scale:

 

The basic strip is 8mm wide (though the LED part is narrower) so it may be less suitable for the freestanding lamps.

Still, another option to consider.

[Paul H Vigor]

1 hour ago, Mol_PMB said:

Yes, I think this kind of thing is the way forward. They seem to exist in various colours and lengths, though short ones (less than an inch) are hard to find.

Effectively they're a by-product of the domestic LED lamp industry, and so a relatively recent development.

I'll order a few and report back here.

The longer flexible ones might even do a neon sign.

Just a thought: I wonder if they can be cut to length and rewired?

[Mol_PMB]

An update, now that I have received the first batch of LEDs.

I bought these on eBay, where they are usually described as COB LED filaments. Expect to pay in the region of 20p each (depending on length, quantity, seller etc).

Some sellers provide more info than others, but few offer comprehensive data and some is very generic for a range of different LEDs.

 

Here are the ones I bought, shown on graph paper with 1mm grid spacing:

 

The ones on the left were described as "10PCS 3V Super Bright COB LED Solar Filament Bulb Candle Light Home Lamp Source", costing £2.10 including postage from China, and some of the specifications given are as follows:

• Lumens: 20LM
• Voltage: 2.9-3.1v
• Amperage: 1A
• Wattage: 0.15（W）
• Filament length: About 26mm
• Light color: Warm white(4200K), white(6500K)
• Color: As show [a warm white light is shown]

 

Now unless Ohm was badly wrong, the volts, amps and watts aren't consistent. I won't try giving them a whole amp of current to start...

Another thing to note is that the 'about 26mm' length is rather approximate. The overall length over the wire connections is typically 29-30mm, while the length of the moulded part is 22-23mm and I suspect the illuminated length is less.

One of the end connections has a hole in it; it seems that the convention is that this is the positive end.

They are rather fragile and one of them arrived with a crack in the moulded part. They certainly can't be bent, and probably need to be handled quite carefully.

 

The ones on the right were described as "10pcs LED COB filament individual DIY loose parts Candle Light Lamp Source 3V", costing £4.79 including postage from China, and the listing offered a choice of colours, lengths and voltages. I chose cool white, 18.5mm and 3V.

The specifications given are as follows:

• The filament is suitable for lighting, crafts, signage and any application that requires a beam of light, it can be powered by low voltage, 2 AA batteries or 3V button cell batteries, it is not bendable, this product is fragile, please contact us to deal with it if you receive it in a broken condition.
•  LED filaments available in 18.5mm,26mm,38mm,54mm,68mm 
• Specifications: Pins at each end, positive pin denoted by dot/hole 
• 130mm filament Width: 2mm 
• Voltage: 2.8-3.3V DC 
• Max current 100mA  
• 300mm filament Width: 2mm 
• Voltage 2.8-3.3V DC 
• Max current 200mA 
• Note: cannot be cut to resize If you should have any questions please get in touch  

In this case, the length of 18.5mm seems to be an accurate measure of the overall length over the wire connections; the moulded part is only 11-12mm long.

 

Having looked at other listings and specifications, it seems that convention is that the specified length is normally the overall length over the wire connections, not the length of the moulded part or the illuminated part. When I ordered these, I had assumed that the quoted length was the moulded part, so the ones I've ended up with are shorter than expected. I have since ordered some more lengths to try. The commonly available lengths seem to be 26mm and 38mm. 18.5mm, 54mm and 68mm also available but with less choice of sellers and other options.

 

 

I've tried applying some electricity. I used a new 9V battery and a 1.4k resistor to start with (being cautious). Please forgive my very crude setup!

In theory, if the forward voltage of the LED is 3V, then the current would be about 4mA.

This was enough to light both types of LED fairly dimly. They produce illumination in all radial directions.

• The shorter one produced a continuous light over about 8mm length (i.e. most of the length of the moulded part) in 'cool white' as advertised.

• The longer one produced 7 distinct spots of light spaced about 2mm apart along the moulded part, in 'warm white' as expected. However, these were only visible to the naked eye and the phone camera did not resolve the spots.

• The cracked one lit up at one end but not the other.

I don't know whether spots vs continuous is a normal difference between short and long LEDs, or if it relates to the manufacturer or quality. In viewing it doesn't matter much.

I also tried a 5.1k resistor; there was still enough current to light the LEDs but they were dim, and in this case the phone could almost resolve the spots.

 

With a 1k resistor they were of course a bit brighter, probably an appropriate brightness for a model.

In normal use in domestic light bulbs I expect they run at much higher current and are blindingly bright.

 

So I think these look like they have promise. I'm wondering whether I can create a prototypically shaped light fitting in brass which acts as one conductor, and then a fine insulated wire for the other end. Watch this space...

 

[Mol_PMB]

I've started making a couple of prototype strip lights.

I'm using a broken 26mm COB LED as a template, but I'm sizing these for 38mm LEDs which are presently on the slow boat from China.

I work in 7mm scale, so a 5' long striplight (a common length) would be 35mm, which suits the 38mm (length over wire ends) LEDs.

I'm using brass channel with outside dimensions of 3mm x 2mm (5"x3.5") which is a bit oversize but not too bad.

At one end I've cut off the flanges, drilled a hole and folded up the end. The negative end of the LED will be soldered through this hole and trimmed off.

 

Near the other end of the channel, I've drilled a hole in the web which should align with the hole indicating the positive end of the LED. I'll solder a wire through the hole in the LED, then pass it through the hole in the channel web (with some sleeving for insulation. I'll also use some small blocks of plastic strip to physically mount the other end of the LED within the channel.

Hopefully this will work and look a bit like a strip light!

 

Watch this space for progress, once the 38mm LEDs have arrived.