Why Forward Voltage of UV LED is so damn high ?

I found a few spec of UV LED, they are about 5V to 6V. Anyone know why UV LED forward voltage is so high compare with normal LED which is about 1.5~2.5V ?

Is there low forward voltage UV LED available ?

Hi,

This is a device physics question. Non trivial. Essentially the band gap (voltage values that do not cause conduction) must be higher to create short-wavelength photons.

The gory details HERE

The link is interesting. Thank you so much.

hamisu-anguan:
I found a few spec of UV LED, they are about 5V to 6V. Anyone know why UV LED forward voltage is so high compare with normal LED which is about 1.5~2.5V ?

Simple: to generate a 5eV photon takes 5eV, which requires 5 volts for an electron-hole pair recombination.

Is there low forward voltage UV LED available ?

no

1 Like

Long wave UV LEDs run on 3.3V, for example this one.

It's really nice that the voltage required to turn on a LED of a particular colour correlates so well with Planck's work.

He figured that E = hv for photons.

So a red LED has a voltage drop of about 1.7 v, and 1.7eV is the energy of the photons produced.

etc for various colours - including UV

Practical quantum physics..

Allan

jremington:
Long wave UV LEDs run on 3.3V, for example this one.

395 to 400nm is in the visible spectrum, not really UV. All the ~3V green/blue/violet/white LEDs you
get these days are high efficiency gallium-nitride (GaN) devices, the colour being tuned by heterojunction/
quantum well techniques, so they run at bascially the same voltage being the GaN bandgap.

Here's a UV LED: https://uk.rs-online.com/web/p/uv-leds/8801494/

MarkT:
Here's a UV LED: https://uk.rs-online.com/web/p/uv-leds/8801494/

How much! :o :o

MarkT:
395 to 400nm is in the visible spectrum, not really UV. All the ~3V green/blue/violet/white LEDs you
get these days are high efficiency gallium-nitride (GaN) devices, the colour being tuned by heterojunction/
quantum well techniques, so they run at bascially the same voltage being the GaN bandgap.

Here's a UV LED: https://uk.rs-online.com/web/p/uv-leds/8801494/

Yes, what he said ! ! !
Baffle em with science. :o :o
Great man, Max Planck.

395 to 400nm is in the visible spectrum, not really UV.

The manufacturers disagree with you.

jremington:
The manufacturers disagree with you.

They're lying.

The device listed gives 2mW at 278nm, and costs £41....

The claim it's high power and suitable for sterilisation.

Hmmm. Steriliising what? Ants?

How much does a cobalt-60 gamma source cost?

Allan

allanhurst:
How much does a cobalt-60 gamma source cost?
Allan

It's the cost of the on-off switch there that makes the difference.

So what is the actual color of the unvisible ultra violet radiated by the UV-C LED at 200-260nm ?
Seem there are in non-visible spectrum, the colors shall be unvisible or the LED still radiate violet color which is in visible spectrum ?

Many people can see 395nm. Some people cannot see 405nm.

This LED peaks at 278nm, which is well down in the UV - I wouldn't expect it to have any visible output, but there may be something else either glowing or fluorescing. Technically it is UV C, but it's right on the cusp of UV C and UV B, (much like 395 is technically UV.) I wouldn't expect it to be especially fast at sterilizing, especially if you are used to using a mercury lamp. Those are typically one to two hundred dollars, and have a limited lifetime. Maybe if you could get a lamp with many of these LEDs, it would be competitive with mercury?

I've used a small (9 watt?) linear UV tube for erasing eproms and exposing photoresist.

It works fine, and a darn sight cheaper than £41..... don't know what spectrum or power output it has.

Allan

Allanhurst - most uv linear tubes are mercury, the peak output is close to 254nm.

Just checked on the lamp specs - A Phillips TUV 8W device.

see http://www.assets.lighting.philips.com/is/content/PhilipsLighting/fp928001104013-pss-global

Peak output about 2.4W at around 250nm. Life 11,000 hours. About £5 for a new one.

You'd need a lot of those 2mW semiconductors to do a similar job....

Allan

edit: ps... It seems they're also used in swimming pool sterilisation plants.

hamisu-anguan:
So what is the actual color of the unvisible ultra violet radiated by the UV-C LED at 200-260nm ?
Seem there are in non-visible spectrum, the colors shall be unvisible or the LED still radiate violet color which is in visible spectrum ?

You’ll probably see a violet halo around the device caused by your eye lens fuorescing as you rapidly develop cataracts and corneal burns! The actual UV cannot get to your retina directly. This fluorescence will be visible
to someone else looking into your eye too, as will the fluorescence of your skin. This radiation is ionizing and
burns and risks skin cancer, so don’t do this experiment!