Normal penlights or mini-flashlights are not very bright.
This is for a number of reasons. The bulb can't be very big physically,
the filament is smaller, the available voltage may be smaller, the available
current is almost certainly much smaller. Special halogen bulbs are
very bright but they go through the current quickly resulting in a fading
brown lamp in only 5 to 8 hours.
What's the answer? There's a new LED (light emitting
diode) that's been produced which is 500 times brighter than your average
LED. You can also buy these in white, yes, white.
The current is only 30mA so this project will work with
even flat batteries - you don't have to buy new ones. The LED will give
full brightness with new batteries for about four days (not just 8 hours)
and looks like it's at least 10 times brighter than an average light
Here's the guf. Drill a slightly wider hole in the battery
holder where the wires are coming out and push the LED through it from
the inside. You MUST use a resistor in series with the LED to limit
the amount of current through it. If you do not (ie, you attach the
LED directly to the batteries) then the LED will flash brightly once
and then never again.
Equipment available from Dick
Smith Electronics as of writing.
- Battery holder (3AA cells and switch) $1.65 #S6153
- Super Bright White LED, 5600mcd, 3.6V, 20mA, $9.95,
- Resistor 33ohm $0.12 (orange orange black gold)
If you don't mind a green colour then the following
LED is even brighter with a narrower beam:
- Super High Intensity Green LED, 10000mcd, $9.95,
You will probably have to use a different resistor with
it of course. Work it out using V=IR
eg. using the new 8,000mcd white LED, 4.0V, 30mA
Use 3 x 1.5V batteries in battery pack = 4.5V but we only want 4.0V
across the LED.
So we need a resistor that can soak up that 0.5V while allowing a current
V = I R or R = V/I
0.5 = 0.03Amps x reistance or R = 0.5/0.03 = 17ohms
Now, when you buy the resistor get one or two of slightly
different values. Connect the LED up and measure the current with a
digital multi-meter. You may find the voltage drops a bit when there's
a load on it or if you're using flat batteries which means using a slightly
lower value resistor to achieve the current you want. (That's why I
suggested the 33 ohm resistor for the 5600mcd LED rather than a 45ohm
p.s. Yeah, the green LED is realllllly bright. Being
green makes anything red look black though. The white ones are better
for seeing with.
More about the future
of LED's and what an LED is (and why we might be able to use them
Parts update October 5, 2001 -- Now Available
Z4015 Super Bright 14,000mcd green LED
Z3982 Super Bright 8,000mcd white LED
mmmm, now that's bright!