White LED Efficiency in Small Lights
| |
CCrane Expedition
|
Maglite 3D
|
Power Supply
|
3 'C' Cells (4.5 V nominal) |
3 'D' Cells (4.5 V nominal) |
Bulb
|
7x Nichia 4.8cd white LEDs |
RadioShack XPR103 Xenon Lamp (rated at 3.6V) |
Current
|
300mA (overdriven LEDs 42mA) |
800 mA |
Power
|
1.35 Watts |
3.6 Watts |
Efficiency
|
15-20 lumens/Watt (@20mA) |
~6 lumens/Watt |
Expected Brightness
|
~16 lumens (more experimentation needed) |
~21 lumens (more experimentation needed) |
Battery Lifetime
|
40hours (full brightness)
100hrs (usuable light) |
~15 hours |
Bulb Lifetime
|
10,000 hours |
36 hours |
Price
|
$60 |
$20 |
SPD
|
|
|
Other Features
|
Special version commissioned
by U.S. Military |
Can be used as a hammer in
an emergency |
LEDs are well suited for small voltage lights such as
flashlights:
- Because of the low voltage requirement, incandescents
must use a thinner filament at a cooler temperature,
which reduces efficiency.
- As voltage decreases, the incandescent runs cooler (decreased
resistance), causing it to draw more power. In the LED
light, as voltage decreases the LEDs increase resistance,
causing it to draw less power.
- As the filament runs cooler, the incandescent becomes
less efficient, producing less light, and of a lower
color temperature (yellow). In the LED light, at reduced
power, the LEDs actually are more efficient, with no change
in color temperature.
- The threshold voltage when LEDs will no longer produce
light is much lower then in an incandescent. Used batteries
that can no longer produce light an incandescent will still
light up an LED.
Although the Maglite draws about twice as much current as the
Expedition, the lifetime of the Expedition is over eight times as
long. Futhermore, the Mag runs on D batteries, which have almost
twice the amount of energy as C batteries. A more comparable LED
light is the LightWave 4000
(view a runtime chart).
This light has 10 LEDs and is about
50% brighter then the Expedition. It runs on 3 D batteries, it's
battery runtime of over 600 hours.
An additional feature about flashlights is that they will be
used at night. Scotopic vision (night) favors the blue/green/yellow
wavelengths which are more prevelant in the light from the
Expedition.
The most recent generation of LED flashlights have
incorporated DC "step-up" circuits to convert the 100
hours of lower voltage light to perhaps 40 hours of full voltage
light. Such a feature would be wasted on an incandescent light,
as it would only provide perhaps only 1 addional hour of light.
Implementing this circuit allows the light to efficiently drain
all the energy from the batteries. An interesting side effect of
this feature is that a lower voltage power source can be used to
power the light. For example, a single 1.5V battery can be used
to drive a light that is rated at 3V. Of course, this will only
provide half the runtime, but with such long runtimes already,
consumers might prefer a smaller and lighter product.
A great flashlight manufacturer that manufacturers lights with
a DC step-up circuit is Arc
Flashlight
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