High voltage indicator LEDs?

[calzap]

Curious as to whether there are  intrinsically high-voltage indicator LEDs on the horizon.  As voltages rise above 12 V, a resistor current-limiter becomes less and less efficient with most of the energy being expended by the resistor.  LED drivers, which are basically current-limited PSUs, are more efficient but add expense and bulk.  Capacitor-based current limiters for AC aren't really better than a LED driver.  After an AC safety capacitor, reverse current diode, fuse, bleed resistor, and in-rush resistor are added, cost and bulk approach that of a solid state driver.

So it would be great if there were LED's or other light-emitting chips that could be used directly with 24, 120 or 240 V.  There are some flat LED's designed for overhead lighting that can be used with 60 V.  Seoul's MJT type is an example, and internally is effectively a bunch of LEDs in series on one chip. What are the prospects for a low light output, low current, cylindrical 3-5 mm or smaller form, the type used as indicator lights as opposed to lighting?

Mike in California

[NiHaoMike]

A blue LED with a high value resistor in series consumes little current even with a relatively high supply voltage. Also look into neon bulbs.

[bktemp]

A modern LED gives more light output than a neon lamp at the same low current. For low light output this is ok. For high power LEDs there are a some specialized off line LED driver ICs working in buck or flyback mode.

[dannyf]

It probably depends on the current capabilities of this "high voltage" source.

Most high voltage sources have very little current capability. In those cases, an emitter follower would be advisable.

[richard.cs]

Given the LED physics dictates the forward voltage any such device would necessarily have either a built-in regulator or a series string of dies. I see the latter as being more plausible and in some situations quite useful giving good brightness on tens of microamps (at 10 dies / 35V or so). It would be quite an expensive part to make and probably not enough demand to make it to market.

Top tip - for lower current neon indicators increase the series-R beyond that needed to keep them struck but put a capacitor (possibly with its own series resistor to limit the current) across the neon. The neon will blink brightly rather than lighting continuously. :-)

[ovnr]

Well, Seoul Semi has the Acrich series, which are line-powered (... if you're in the US or any other country with wimpy mains). Here are some of them - they also do complete modules.

Sure, they're not exactly indicators.

[calzap]

I'd rather stick with LED indicators rather than neon and use resistive current limiters up to 24 V and drivers for >24 V.  The range of sizes, shapes, colors, brightnesses and other features (flashing, flickering, multicolors, etc.) is unbeatable by neon.  I don't think neons can be started with less than about 50 V.  Just wish the need for drivers would go away.

Mike in California

[thm_w]

These are not small, but have been around for a long time: http://www.ebay.com/itm/Green-LED-Indicator-Pilot-Signal-Light-Lamp-24V-/121373653361?pt=LH_DefaultDomain_0&hash=item1c426ef971

For the one I've used the internal module was maybe 5-8mm in dia. Looked very similar to this digikey part: http://www.digikey.ca/product-detail/en/MT106F-UG/1125-1214-ND/4249236

But those are not cheap, and kind of odd dimensions.

[dannyf]

If it is a real power source, you may try a voltage regulator configured as a ccs.

[lapm]

A blue LED with a high value resistor in series consumes little current even with a relatively high supply voltage. Also look into neon bulbs.

Where i work  we have few liquid valves that has those blue leds. Damn bright and clearly visible from several tens of meters away... My eyes are bit unusually sensitive to wavelenght used in those... Noticed same effect on blue led christmass lights...

[SeanB]

Blue LEDs and red led's are very efficient. I made some power indicators using 33k resistors in series to get around 100k, replacing a neon indicator. It casts a dot on the far wall in dim light. I bought one of those Chinese voltage standards, and changed the blue charge indicator resistor out from 470R to 10k, just to get the brightness down to the point where it was not lighting the room at night. It still is very bright.

[djococaud]

Blue LEDs are not the most visible (the eye best sensivity is more around the geen wavelength). The best is green or orange (or red for efficiency), or even white (look at car dashboards, wich are never blue).

In those days, most LED color are quite efficient though.

To power Led with 240Vac, I would go with a small series capacitor (say...100nF/400V), wich is way more efficient (but you must power it with AC)

[SeanB]

Blue LEDs are not the most visible (the eye best sensivity is more around the geen wavelength). The best is green or orange (or red for efficiency), or even white (look at car dashboards, wich are never blue).

In those days, most LED color are quite efficient though.

To power Led with 240Vac, I would go with a small series capacitor (say...100nF/400V), wich is way more efficient (but you must power it with AC)

My VW Polo has a blue dashboard, along with a lot of the 2000-2010 VW products.

[djococaud]

Blue LEDs are not the most visible (the eye best sensivity is more around the geen wavelength). The best is green or orange (or red for efficiency), or even white (look at car dashboards, wich are never blue).

In those days, most LED color are quite efficient though.

To power Led with 240Vac, I would go with a small series capacitor (say...100nF/400V), wich is way more efficient (but you must power it with AC)

My VW Polo has a blue dashboard, along with a lot of the 2000-2010 VW products.

Oh, my bad, It' s true that some cars now have blue dashboards (for nice design).
I like fancy blue dashboards but, is it easier or more difficult to read ? because of the blue glow that emmits ? (we are a bit off-topic but I would like to have your impressions ! )

[eneuro]

Oh, my bad, It' s true that some cars now have blue dashboards (for nice design).

I'm not sure if blue dashboard looks realy nice?
I like my orange Peugeot displays with blue only for long distance lights.
However, If I had a choice I prefere green displays.

This how our brain works and retina sensitivity determines this 
Visible Light and the Eye's Response

[jmoreland79]

Oh, my bad, It' s true that some cars now have blue dashboards (for nice design).

I'm not sure if blue dashboard looks realy nice?
I like my orange Peugeot displays with blue only for long distance lights.
However, If I had a choice I prefere green displays.

This how our brain works and retina sensitivity determines this 
Visible Light and the Eye's Response

I think people prefer a blue backlit dashboard because they're less sensitive to it.  My Acura has it and I prefer the blue backlight as it's less "in your face," particularly at night opposed to a white or red-orange backlight.  But I'm sure overall it's a matter of personal preference.

[SeanB]

Blue backing, red lit pointers against the lettering is easy to read at night. You do have an issue during twilight that there is too much outside glare.

The attached is one i took a while ago at night.

[eneuro]

I prefer the blue backlight as it's less "in your face," particularly at night opposed to a white or red-orange backlight.

Light sensor should adjust its backlight  illumination 
I wonder If it is controlled by car CAN bus or maybe simply built light sensor into dashboard?
But ok it is off-top maybe in another thread, however auto adjusting backlight in electronics front panels is nice to have feature 

Back to this topic- I need to add another 230VAC low current LED indicator too in my solder station panel and I do not remember how big resistor i've put, but 100k looks good in simply circuit simulation and computed power by hand looks like 0.127W, while this 1000V diode in series to protect LEDs low reverse voltage cuts half of this 50Hz AC wave?