supernatural flashlight

[wow_cn]

my friend is a led flashlight DYIer. yesterday he met a supernatural thing, that was the flash light could not be turned on at light place. if he moved it to darkness, the flashlight can be on. very puzzled!!!:thinking:
note: the led driver is 3*7135+mcu, led is CREE P4. no any light sensor in it!
if you want to see vidio, you can visit:
http://www.tudou.com/programs/view/R-jcS80EtJs/

 

[LukeA]

Every LED is also a photodiode, like every motor is also a generator.

 

[PhotonWrangler]

What LukeA said. Also, a marginally operating neon nightlight bulb will tend to ionize (light up) in the presence of light rather than darkness. It's the same principle.

 

[wow_cn]

haha ....
AMC7135 is only 350ma chip. we use more than 100 pieces 3*7135+mcu and no this happaned. i understand what you say, but can you make this for me? haha ...

 

[frenzee]

Yep, I concur about the neon nightlight phenomenon. In fact, if you have one that starts to flicker in the dark, it's because it has now turned into a crude cosmic ray and back scatter radiation detector, and if you put two of them in close proximity, the flickering will be more or less synchronized.

What LukeA said. Also, a marginally operating neon nightlight bulb will tend to ionize (light up) in the presence of light rather than darkness. It's the same principle.

 

[PhotonWrangler]

Yep, I concur about the neon nightlight phenomenon. In fact, if you have one that starts to flicker in the dark, it's because it has now turned into a crude cosmic ray and back scatter radiation detector, and if you put two of them in close proximity, the flickering will be more or less synchronized.

Whoa... I never realized that, but it makes perfect sense! Now I'm going to have to try it for myself. Thanks for the idea, frenzee! :huh:

 

[M@elstrom]

What LukeA said. Also, a marginally operating neon nightlight bulb will tend to ionize (light up) in the presence of light rather than darkness. It's the same principle.

Um how does a light engine lighting up in the presence of light rather than darkness explain a torch that can't work in a lit environment but will in a dark one?

 

[PhotonWrangler]

The changing ambient light changes the photovoltaic potential across the LED. It's possible that the LED's driver is operating marginally and the presence of light falling on the LED causes the bias on the driver to change.

BTW I just tested a 10mm blue LED with a vom and I could easily produce +2vdc from the LED by aiming my River Rock 2AA flashlight at it.

It's not just an LED, it's a bidirectional transducer!

 

[wow_cn]

The changing ambient light changes the photovoltaic potential across the LED. It's possible that the LED's driver is operating marginally and the presence of light falling on the LED causes the bias on the driver to change.

BTW I just tested a 10mm blue LED with a vom and I could easily produce +2vdc from the LED by aiming my River Rock 2AA flashlight at it.

It's not just an LED, it's a bidirectional transducer!

yes, you are right!
i tested P4 led and got 1.8VDC. Different Led gives different voltage. Some is small and some is higher. My friens began to make light sensor torch(only use led to detect). :twothumbs