Hi,

Theoretically it is certainly possible to transmit 'power' at a distance using light, that is what some of the most advanced weapons of today are doing. It does take some work though, and a decent level of transmit power.

The main things to consider:
1. The transmit power.
2. The transmit radiation pattern and area.
3. The receiver area and efficiency or just the overall efficiency.
4. The distance.

For example, if your transmitter puts out 1 watt over 1 square inch and there is little or no dispersion and the receiver has 1 square inch area and the conversion efficiency is 10 percent then the amount of power that you get out is 100mw. However, if the radiation pattern is such that it spreads out to 4 square inches at the receiver and the receiver only has 1 square inch detection area, then you loose another 75 percent which takes this down to 25mw. This means a lens is recommended to help keep the pattern focused.
If you use a laser rather than an LED, then it's a little better,but that can also start to get dangerous.

The required power is, lets keep it simple with some room for error, 1ma times 4 volts which is 4mw. If you use a lens you might get away with 40mw, but i'd shoot for higher. A 500ma LED should get you there.

 

Mmmm,
dangrious, yes; probably should have mentioned that sorry.
Head was in flight of fancy mode thinking about salvaged laser LED's as opposed to actually considering the ramifications.

It raises an interesting point though. Obviously a laser is a serious risk to your sight, more so a visible one and even at relativly small outputs.
How much risk is there with a 0.5W source columnated to a couple of Cm squared?
I expect there is some energy density that is likely to damage but w/mm ?
anyone know?
Kind of makes you wonder about 8W, or even bigger, torches...

Al

 

Mmmm,
(Some text removed for clarity)

It raises an interesting point though. Obviously a laser is a serious risk to your sight, more so a visible one and even at relativly small outputs.
How much risk is there with a 0.5W source columnated to a couple of Cm squared?
I expect there is some energy density that is likely to damage but w/mm ?
anyone know?
Kind of makes you wonder about 8W, or even bigger, torches...

Al

The risk is that without proper protection (laser safety glasses for the specific wavelength(s) involved a brief glance at a stray reflection could easily permanently damage your eyes.

This discussion is helpful as an example for educational purposes, but if it moves toward practical implimentation this thread may be closed.

 

Hi,

The energy density from the Sun is about 1000 watts per square meter. That's 100mw per square centimeter, about 0.645 watts per square inch.

1 watt per square inch can raise the temperature of 1 square inch of area (with only natural air flow and no heat sink) by 60 degrees C.

So it is unlikely that 500mw will cause a fire, but it could cause something to melt such as plastic. It's close to the density of the Sun though so damage to the eyes is very probable with a direct view.

 

You don't see a lot of people staring at the sun for very long....