Datasheet
•
flux [
Φ
e
and
Φ
V
]
•
wavelength [
λ
] resp. color [x
2°
/ y
2°
] and color temperature (T
CT
).
The influence of the current on these parameters is often similar to the impact caused by
temperature which we will see later.
Influence on lifetime
Overdriving an LED chip, i.e. exceeding its forward current I
F
over the allowable maximum, will
damage the chips within a short time. But long term high current effects also influence a
decreased lifetime: The lower the current, the longer the lifetime for the chip and the whole
ACULED product. Since the degradation processes behind this truth are very complex and not
fully understood today, it is virtually impossible to get reliable curves of t
Life
versus I
F
today.
Influence on forward voltage
The characteristics of the forward current I
F
versus the forward voltage V
F
were already
discussed and shown in the chapter “The Electrical Principle of LED”. Figure 2 in this chapter
shows typical curves for red, green, and blue chips of the ACULED.
Influence on flux
The flux
Φ
e
and
Φ
V
and their deducted values, such as luminance, radiance, luminous intensity
or radiant intensity, increase with the current. Unfortunately this happens not linear. Saying it in
simple words: Doubling the current usually does not double the light output, particularly not at
higher currents. Figure 10 shows typical curves representing the luminous flux for the chips of
the RGYB ACULED VHL. These charts can be found in the specific datasheets of the ACULED
VHL products.
Figure 10
Typical flux vs. current
characteristic of an LED shown by
the example of the ACULED VHL
RGYB at 25°C board temperature.
The color of the curves responds to
the emitted color of the chips.
Influence on wavelength resp. color
The change of the wavelength (
λ
peak
resp.
λ
dom
) and, therefore, the color versus the current, is
shown in figure 11. Again, it is not linear and depends on the material and the color of the LED
chip.
We can easily see that adjusting intensity of an LED product by the current is very difficult and
needs a calibration of the driver to the individual chip characteristics. The same applies to
adjusting colors, for example in a multi color chip ACULED, which is done by weighting the ratio
of the intensities of each individual color to a wanted mixture. All these effects described here
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Driving the ACULED® VHL™ 10