Old-Style "Edge Lit" Bulb - Does anything like this still exist?

Some industrial MBC style "bulb replacement" LEDs have a LED that has a concave front. That reflects a lot of the the light to the sides.

From a quick search, similar individual LEDs are readily available online:

That style, with a drop of aluminium/silver paint in the front to enhance the radial reflection, could work well??

The cool thing about the old (odd?) style bulbs is that they have a finished part in front of the panel that emits no light, and with the threaded socket on the back of the panel, it's clamped to the panel.

The application was pretty specialized when it was built, possibly during WWII or shortly thereafter, but it seems like it would be very useful today. The small box I got at the surplus store was a bomb release control I believe. It had a 7 position Ledex switch which I suppose automatically cycle from one bomb to the next when the release button was pressed.

You could 3D print small discs with shallow spigots to blank off the front of the LED holes.

I played around with illuminated panels some decades ago.. One alternate that may work is part drill some holes in the back of the panel, behind where you can attach a label to conceal them from the outside - then illuminate the holes from the back. The drillings will deflect light into the panel.

I used chamfered edges on some things I did, with the chamfer painted silver and lit from the back, inside the enclosure.

Once you have internal illumination in the panel, punched dots or scribed lines glow nicely!

It's more of a curious question at the moment, an idea waiting for an an application

The bayonet style and leaded grain-of-wheat are still available: aircraftspruce.com/catalog/pnpages/11-12784.php?gad_source=1&gclid=EAIaIQobChMI4_va1_PugwMVj11HAR2rWArXEAQYCCABEgJchPD_BwE

Amazon also has the grain-of -wheat. Its bayonet version appears to be LED. For general aviation, I don't recall seeing a threaded version (circa mid 60's to 90's).

The bulbs I'm thinking of may have had a bayonet base. Sometimes the details dim after 50 years (my calendar must be lying again!).

The bulbs in question had a fixed black (opaque) cap on the end as shown on the picture (everything pictured except the hashed acrylic panel is the bulb – one piece that can't be disassembled). It inserted from the front of the panel, with light emitted from the sides only.

The bulbs may have been painted by the instrument maker. Many of the bulbs I had were painted blue or had a transparent blue polymer cap. I just used transparent blue lacquer if the cap was not reusable.

The bulbs were clear.

The key point is the opaque end of the bulb that held it captive to the panel.

For The Popcorn said:

Way back when (the 70s) I bought an old aviation switch box at a military surplus store. It was a small treasure chest, including a Ledex (rotary relay) and other cool stuff. It had a painted acrylic panel with engraved labels, which were illuminated by very interesting bulbs.

These bulbs were an opaque thin disk on the surface of the panel (no light visible), with the clear part of the bulb located within the panel thickness, and a threaded base to screw into a socket. There's a picture below. The effect was to edge-light the painted acrylic panel, so the labels were visible. I've never seen bulbs like this otherwise.

Have you seen anything similar today, possibly in an LED format? Something like this would be extremely handy to edge-light a laser-engraved piece of acrylic.

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Lowe's and Home Depot has those, I saw them last week I was looking for light for our camper trailer. They also have U shape lights.

gary350 said:

Lowe's and Home Depot has those, I saw them last week I was looking for light for our camper trailer. They also have U shape lights.

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Doubtful. These are small bulbs - say ¼" bulb diameter.

For The Popcorn said:

Doubtful. These are small bulbs - say ¼" bulb diameter.

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All of their products are available online - did you check instead of just doubt?

What's the point of this post?
A simple LED strip is very directional so it doesn't need o be encapsulated 360° by the acrylic like an incandescent, neon or fluorescent bulb to maximize the light extraction for total internal reflection in the clear PMMA.

Simply mount the clear panel tight to the LED strip and wrap the rest of the panel with reflective white tape to "recycle" the light flowing all the way across the panel. LED edge-lit TVs and monitors have used this technique for years.

In summary, I highly disagree with your hypothesis that an obsolete illumination technique would be...

For The Popcorn said:

...extremely handy to edge-light a laser-engraved piece of acrylic

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A simple LED strip on the outer edge works just fine - and no wires in the field-of-view behind the clear panel.

Laptop screens once used CCFL tubes to flood two edges of glass with light and plastic diffusers to reflect the light out evenly to the LCD. Digikey used to sell them.

For The Popcorn said:

Doubtful. These are small bulbs - say ¼" bulb diameter.

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like Xmas lights?


8mm stripleds are pretty inexpensive now.

you could try Phil at fairradio.com
Lot of old military radio and parts.
Also https://beechcrafthm.org/
There is a group there that restores old equipment. I sold them old military parts last year

May try other avionics museums

Thanks all. This was mostly a question of curiosity. I hadn't seen these bulbs anywhere else, but unlike many here, I don't believe I know everything.

Rowmark Plastics has some interesting materials like Color Hues that I've under to make low-cost panels for short-run projects.

Color Hues are a panel with 3mm clear acrylic with a hardcote surface for amazing wear resistance. The back surface of the material is the thin color layer, which can be laser-etched to provide labels and artwork. The engraved areas are filled with acrylic paint ( literally slopped on) for color.

But a unique way to use the material is to illuminate the etched areas from behind with LEDs. Using this technique, I was able to replace expensive illuminated industrial switches with longer-life tactile switches with an illuminated ring around the button.

I'm told by one of the moderators that I have a heckler in this thread. Fortunately, I don't see his comments as he was blocked long ago. I understand he thinks this whole question is rubbish and pointless – that edge lighting is always the right answer. Well, it's a pity he didn't understand my post – the original purpose of these lamps was to illuminate a painted translucent white acrylic panel where labels had been etched through the painted layer. In many cases, there's not room to edge-light a panel, and as the panel is opaque, there's not problem with wires running from the middle of the panel. In fact, if sockets for the bulbs are pcb-mounted, they might serve the dual purpose of illumination and securing the panel.

For The Popcorn said:

it's a pity he didn't understand my post

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Not so much of a pity if he was blocked anyhow.

How unfortunate that he assumed you were talking about edge lighting when, in your first post, you actually meant edge lighting.

For The Popcorn said:

The effect was to edge-light the painted acrylic panel, so the labels were visible.

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For The Popcorn said:

Something like this would be extremely handy to edge-light a laser-engraved piece of acrylic.

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Tony Stewart said:

Laptop screens once used CCFL tubes to flood two edges of glass with light and plastic diffusers to reflect the light out evenly to the LCD. Digikey used to sell them.

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Later ones use LED's to do the same, as do most TV's - often they only flood one edge, it always amazes me how even they can get the light in this way.

I know I'm late to the party, but LCD backlights are side mounted, I've replaced a few. they are rectangular rather than round, but the facia would need to be painted white behind for the light to fill the area,

I bought these and slotted them in..
As Nigel said, they almost ge to the other side on a 20 x 2 large character