DOCTER DOCTER®aspherilux midi LED - Manual (Page 15)

15
Glossary of Technical Terms
LED Efficiency
Contrary to popular opinion, the efficiency of light emitting diodes is not close to
100%. This assumption arises from the hardly perceptible heat build-up in the
typically very low power consumption of a small-sized LED. Virtually, the efficiency
is comparable with that of a fluorescent lamp and even higher. The high
performance of the used LED leads to a significant power dissipation that requires
the LED to be cooled passively. Such cooling is accomplished through the casing.
In case of longer usage, the casing may heat up noticeably.
Nickel Metal Hydride Batteries
In this lamp, NiMH batteries are used that have no memory effect and are free of
harmful substances such as cadmium and lead. In contrast to the classic memory
effect, the so called lazy battery effect may also occur in the Ni-MH technology.
The causes are basically the same as with the classic memory effect (permanent
charges or partial discharges only). They, however, affect the positive nickel
hydroxide electrodes that, in case of Ni-Cd and Ni-MH, correspond to each other.
Here, the charging voltage decreases slightly only.
Hence, it is recommended not to leave the DOCTER
 aspherilux midi LED in the
charging station permanently, but to have it discharged until occurrence of the
battery warning signal and to recharge in case of need only.
Working Temperature
When a battery cell is discharged, electrochemical processes are going off.
Depending on the temperature, these processes are accelerated or decelerated.
Hence, in case of a low ambient temperature, only a small capacity will be
available. It is disadvantageous that NiMH batteries cannot be used at very low
temperatures. Therefore, it is recommended to wear the DOCTER
 aspherilux midi
LED in winter time close to the body.
Storage
The on/off switch also separates the control electronics from the battery pack
permanently in order to prevent any power consumption. Nevertheless, during
storage the available capacity will decrease due to the self-discharge of the battery
cells. In case of NiMH batteries, such self-discharge amounts to 60% per month.
However, when temperatures are low, this self-discharge is decelerated and
amounts to only 30% per month at 5 C. Hence, storage in a refrigerator may be
quite useful.
Basically, it does not matter in what charging condition the DOCTER
 aspherilux
midi LED is stored. In case of any longer storage period (for more than six
months), however, a Ni-MH battery should be stored in fully charged condition and
at possibly low temperatures. Besides, it should be recharged once every twelve
months at least.
Brightness Control
A special feature of the circuit enables the brightness to be kept at a widely high
level even if battery voltage decreases considerably. To this effect, a down
controller is implemented in the circuit. Even if the batteries are approaching the
final discharge voltage and, thus, the end of operation, there will be no decrease in
brightness. Therefore, a warning will be released when the end comes near or
when a warning has already been given and no recharging done yet.
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