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I would like to use white LED to replace bulb, but LED is not as bright as light and the Led light con not travel far.
Q1. Can I place convex lenses in frant of LED to make the light travel further?
Q2. How curve is the convex lenses I have to design ?
- vincent (age 35)
kluang, Johor, Malaysia
The light from an LED will travel just as far as the light from any
other source. The difference is that there's just not very much of it.
The 'intensity' of the light from an LED is very low - it doesn't emit
very many photons per second. Short of using a whole LOT of LED's,
there is really nothing you can do to make an LED's light brighter.
The reason that the LED appears to be dimmer from further distances
is that the light spreads out in all directions. You could use a convex
lens to focus some of the light together so that you could still see
the LED from further away, but you will not actually have any more
light than you did before. It will just be directed more in a beam in
one direction. Basically, you are talking about looking at the LED
through a magnifying glass. The curvature of the lens detrmines how far
away from the LED it should be placed. The distance from the LED to the
lens should be equal to the lens's focal length in order to make the
light from the LED come out in a nearly parallel beam. How much light
gets gathered into the beam depends of how big the lens diameter is and
how far away it id from the LED. Obviously you want a big ratio of lens
diameter to focal length to get as much light as possible. That's the
same a saying you want what's called a small f-number lens.
Since small f-number lenses aren't cheap, you might consider
using a reflector instead. For example, the metallic reflector in a
standard flashlight is designed to do just what you want. You could put
the LED near where the bulb goes, and adjust the position slightly to
get the best beam.
-Tamara (w Mike W.)
(republished on 07/29/06)
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