US 20140217915A1
(19) United States
(12) Patent Application Publication (10) Pub. No.: US 2014/0217915 A1
Shteynberg et al.
(54)
(43) Pub. Date:
REGULATION OF WAVELENGTH SHIFT AND
PERCEIVED COLOR OF SOLID STATE
LIGHTING WITH INTENSITY VARIATION
Aug. 7, 2014
Publication Classi?cation
(51)
Int- Cl
H05B 33/08
(52) US, Cl,
(71) Applicant: Point Somee Limited Liability
Company, Dover, DE (U S)
(2006.01)
CPC ................................ .. H053 33/0854 (2013.01)
USPC
........................................................ ..
315/210
(72) Inventors: Anatoly Shteynberg, San Jose, CA
(US); Harry Rodriguez, Gilroy, CA
(US); Bradley M. Lehman, Belmont,
MA (US); Dongsheng Zhou, San Jose,
(57)
CA (Us)
ABSTRACT
Representative embodiments of the invention provide a sys
tem, apparatus, and method of controlling an intensity and
spectrum of light emitted from a solid state lighting system.
The solid state lighting system has a ?rst emitted spectrum at
(73) ASSigiieei POiiit somee Limited Liability
company, Dover: DE (Us)
a full intensity level and at a selected temperature, with a ?rst
(21) Appl' NO': 14/248,290
electrical biasing for the solid state lighting system producing
_
a ?rst wavelength shift, and a second electrical biasing for the
(22) Flled:
Apr“ 8’ 2014
solid state lighting system producing a second, opposing
.
(60)
.
wavelength shift. Representative embodiments provide for
Related U's' Apphcatlon Data
Division of application No. 13/741,896, ?led on Jan.
15, 2013, now Pat. No. 8,704,456, which is a division
of application No. 11/927,084, ?led on Oct. 29, 2007,
receiving information designating a selected intensity level or
a selected temperature; and providing a combined ?rst elec
trical biasing and second electrical biasing to the solid state
now Pat. No. 8,368,636, which is a continuation-in
part of application No. 11/859,680, ?led on Sep. 21,
intensity level and having a second emitted spectrum within a
predetermined variance of the ?rst emitted spectrum over a
2007, now Pat. No. 7,880,400.
predetermined range of temperatures.
lighting system to generate emitted light having the selected
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FRIYS. .1£?
SELECT TWO OR MORE ELECTRICAL
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BIASING TECHNIQUES WHICH PROVIDE
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TO INTENSITY VARIATION AND/0R
JUNCTION TEMPERATURE
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ELECTRICAL BIASING TECHNIQUE AND/0H
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SELECTED TOLERANCE LEVEL
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CONVERT THE COMBINATIONS OF BIASING
TECHNIQUES INTO PARAMETERS
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US 2014/0217915 A1
REGULATION OF WAVELENGTH SHIFT AND
PERCEIVED COLOR OF SOLID STATE
LIGHTING WITH INTENSITY VARIATION
CROSS-REFERENCES TO RELATED
APPLICATIONS
[0001] This application is a divisional of US. patent appli
cation Ser. No. 13/741,896, ?led Jan. 15, 2013, which is a
divisional of US. patent application Ser. No. 11/927,084,
?led Oct. 29, 2007, now US. Pat. No. 8,368,636, which is a
continuation-in-part of US. patent application Ser. No.
11/859,680, ?led Sep.21,2007,nowU.S.Pat. No.7,880,400,
the disclosures of which are hereby incorporated by reference
herein.
current. For example, in Mueler et al., US. Pat. Nos. 6,016,
038, 6,150,774, 6,788,011, 6,806,659, and 7,161,311,
entitled “Multicolored LED Lighting Method and Appara
tus”, under the control of a processor (or other controller), the
brightness and/or color of the generated light from LEDs is
altered using pulse-width modulated signals, at high or low
voltage levels, with a preprogrammed maximum current
allowed through the LEDs, in which an activation signal is
used for a period of time corresponding to the duty cycle of a
PWM signal (with the timing signal effectively being the
PWM period). See also US. Pat. Nos. 6,528,934, 6,636,003,
6,801,003, 6,975,079, 7,135,824, 7,014,336, 7,038,398,
7,038,399 (a processor may control the intensity or the color
by providing a regulated current using a pulse modulated
signal, pulse width modulated signals, pulse amplitude
BACKGROUND
modulated signals, analog control signals and other control
signals to vary the output of LEDs, so that a particular amount
[0002] Arrays of light emitting diodes (“LEDs”) are uti
lized for a wide variety of applications, including for general
lighting and multicolored lighting. Because emitted light
of current supplied generates light of a corresponding color
and intensity in response to a duty cycle of PWM), and US.
Pat. No. 6,963,175 (pulse amplitude modulated (PAM) con
intensity is proportional to the average current through an
trol).
LED (or through a plurality of LEDs connected in series),
adjusting the average current through the LED(s) is one typi
[0006] These methods of controlling time averaged for
ward current of LEDs using different types of pulse modula
tions, at constant or variable frequency, by switching the LED
current alternatively from a predetermined maximum value
toward a lower value (including zero), creates electromag
netic interference (“EMI”) problems and also suffers from a
limitation on the depth of intensity variation. Analog control/
cal method of regulating the intensity or the color of the
illumination source.
[0003]
Because a light-emitting diode is a semiconductor
device that emits incoherent, narrow-spectrum light when
electrically biased in the forward direction of its (p-n) junc
tion, the mo st common methods of changing the output inten
sity of an LED biases its p-n junction by varying either the
forward current (“I”) or forward bias voltage (“V”), accord
ing to the selected LED speci?cations, which may be a func
tion of the selected LED fabrication technology. For driving
an illumination system (e.g., an array of LEDs), electronic
circuits typically employ a converter to transform anAC input
voltage (e. g., AC line voltage, also referred to as “AC mains”)
and provide a DC voltage source, with a linear “regulator”
then used to regulate the lighting source current. Such con
verters and regulators are often implemented as a single unit,
and may be referred to equivalently as either a converter or a
regulator.
[0004] Pulse width modulation (“PWM”), in which a pulse
is generated with a constant amplitude but having a duty cycle
which may be variable, is a technique for regulating average
current and thereby adjusting the emitted light intensity (also
Constant Current Reduction (or Regulation) (“CCR”), which
typically varies the amplitude of the supplied current, also has
various problems, including inaccurate control of intensity,
especially at low current levels (at which component toler
ances are most sensitive), and including instability of LED
performance at low energy biasing of the p-n junction, lead
ing to substantial wavelength shifting and corresponding
color distortions.
[0007] As described in greater detail below with reference
to FIGS. 1-3, both the PWM and CCR techniques of adjusting
brightness also result in shifting the wavelength of the light
emitted, further resulting in color distortions which may be
unacceptable for many applications. Various methods of
addressing such color distortions, which are perceptible to the
human eye and which can interfere with desired lighting
applications, have not been particularly successful. For
example, in McKinney et al. US. Pat. No. 7,088,059 analog
referred to as “dimming”) of LEDs, other solid-state lighting,
control is used over a ?rst range of intensities, while PWM or
LCDs, and ?uorescent lighting, for example. See, e. g., Appli
cation Note AN65 “A fourth generation of LCD backlighting
pulse frequency modulation (“PFM”) control and analog con
technology” by Jim Williams, Linear Technology, November
Mick US. Pat. No. 6,987,787, PWM control is used in addi
tion to variable current control, to provide a much wider range
1995 (LCDs); Vitello, US. Pat. No. 5,719,474 (dimming of
?uorescent lamps by modulating the pulse width of current
pulses); and Ihor Lys et al., US. Pat. Nos. 6,340,868 and
6,211,626, entitled “Illumination components” (pulse width
modulated current control or other form of current control for
trol is used over a second range of illumination intensities. In
of brightness control by performing a “multiplying” function
to the two control inputs (peak current control and PWM
control). Despite some improvement of intensity control and
color mixing of these two patents, however, the proposed
intensity and color control of LEDs). In these applications for
combinations of averaging techniques still do not address the
LEDs, a processor is typically used for controlling the amount
of electrical current supplied to each LED, such that a par
ticular amount of current supplied to the LED module gener
ates a corresponding color within the electromagnetic spec
resulting wavelength shifting and corresponding perceived
color changes when these techniques are executed, either as a
single analog control or as a combination of pulse and analog
controls.
trum.
[0008]
[0005] Such current control for dimming may be based on
a variety of modulation techniques, such as PWM current
wavelength change may be tolerated, assuming the reduced
quality of the light is acceptable. It has been proposed to
correct this distortion through substantially increasing the
complexity and cost of the control system by adding emission
control, analog current control, digital current control and any
other current control method or system for controlling the
Depending on a quality of the light source, this
Aug. 7, 2014
US 2014/0217915 A1
the emission shift during intensity regulation. See Applica
depending upon the type of solid state lighting and various
other conditions. In addition, various mixes and combina
tion Brief AB 27 “For LCD backlighting Luxeon DCC”
tions of wavelengths are also included, such as combinations
Lumiledes, January 2005, at FIG. 5.1 (Functional model of
Luxeon DCC driver).
of red, green, and blue wavelengths, for example, each of
which generally has a corresponding peak wavelength, and
(color) sensors and other devices to attempt to compensate for
[0009]
Accordingly, a need remains for an apparatus, sys
each of which may have the various narrower or broader
tem, and method for controlling the intensity (brightness) of
ranges of wavelengths described above. Further, the various
light emissions for solid state devices such as LEDs, while
wavelength shifts of emitted spectra may refer to a shift in a
simultaneously providing for substantial stability of per
peak wavelength, corresponding shifts of multiple peak
ceived color emission and control over wavelength shifting,
wavelengths, or an overall or composite shift of multiple
wavelengths, as the context may suggest. For example, in
accordance with the present disclosure, wavelength shifts of a
over both a range of intensities and also over a range of LED
junction temperatures. Such an apparatus, system, and
method should be capable of being implemented with few
components, and without requiring extensive feedback sys
plurality of dominant peak wavelengths for a corresponding
plurality of colors (e.g., red, green and blue) are controlled
within corresponding predetermined variances, in response
tems.
to variables such as intensity, temperature, selected color
SUMMARY
[0010] The representative embodiments of the present dis
closure provide numerous advantages for controlling the
temperature (intensity and wavelength/spectra), selected
lighting effects, other criteria, etc.
LEDs, while simultaneously providing for substantial stabil
[0013] It should also be noted that the various references to
a “combination” of electrical biasing techniques should also
be interpreted broadly to include any type or form of com
ity of perceived color emission, over both a range of intensi
ties and also over a range of LED junction temperatures. The
tive superposition of a ?rst biasing technique with a second
representative embodiments provide digital control, without
including external compensation. The representative embodi
tion of a ?rst biasing technique with a second (or third or
ments do not utilize signi?cant resistive impedances in the
more) biasing technique (i.e., a time interval-based superpo
current path to the LEDs, resulting in appreciably lower
sition, with a ?rst biasing technique applied in a ?rst time
interval followed by a second (or third or more) biasing tech
nique applied in a second (or third or more) time interval); an
alternating of a ?rst biasing technique with a second (or third
or more) biasing technique; or any other pattern comprised of
intensity of light emissions for solid state devices such as
power losses and increased ef?ciency. The representative cur
rent regulator embodiments also utilize comparatively fewer
components, providing reduced cost and size, while simulta
neously increasing ef?ciency and enabling longer battery life
bining, as discussed in greater detail below, such as an addi
(or third or more) biasing technique; a piece-wise superposi
when used in portable devices, for example.
or which can be decomposed into at least two or more differ
[0011] A representative embodiment provides a method of
controlling an intensity of light emitted from a solid state
lighting system, the solid state lighting having a ?rst emitted
spectrum at full intensity, with a ?rst electrical biasing for the
solid state lighting producing a ?rst wavelength shift, and
with a second electrical biasing for the solid state lighting
producing a second, opposing wavelength shift. The ?rst and
ent biasing techniques during a selected time interval. It
second wavelength shifts are typically determined as corre
sponding ?rst and second peak wavelengths of the emitted
spectrum. The representative method comprises: receiving
information designating a selected intensity level lower than
full intensity; and providing a combined ?rst electrical bias
ing and second electrical biasing to the solid state lighting to
should also be noted that providing such a combination of two
or more electrical biasing techniques will result in an applied
electrical biasing which has its own corresponding waveform
which will differ from the waveforms of the ?rst and second
biasing techniques. For example, a combined or composite
waveform may be created by applying a ?rst biasing tech
nique in a ?rst time interval, followed by a second biasing
technique in a second time interval, followed by a third bias
ing technique in a third time interval, followed by repeating
this sequence of ?rst, second and third biasing techniques for
the next corresponding ?rst, second and third time intervals
(periods). The resulting waveform of such a combination may
generate emitted light having the selected intensity level and
be referred to equivalently as a piece-wise or time-based
having a second emitted spectrum within a predetermined
variance of the ?rst emitted spectrum. The predetermined
The combination may be represented in any number of
variance may be substantially zero or within a selected toler
equivalent ways, for example, as one or more parameters, as
one or more control signals, or as a resulting electrical biasing
ance level. The ?rst electrical biasing and the second electri
superposition of the ?rst, second and third biasing techniques.
cal biasing may be a forward current or an LED bias voltage.
waveform. For example, two or more biasing techniques may
[0012]
be selected, having ?rst and second respective waveforms,
It should be noted that as used herein, the terms
“spectrum” and “spectra” should be interpreted broadly to
mean and include a single wavelength to a range of wave
lengths of any emitted light. For example, depending upon
any number of factors including dispersion, a typical green
LED may emit light primarily at a single wavelength (e.g.,
526 nm), a small range of wavelengths (e.g., 5258-5262
nm), or a larger range of wavelengths (e.g., 522-535 nm).
Accordingly, as indicated above, the wavelength shifts
referred to herein should be measured as peak wavelengths of
with the resulting combination utilized to create or provide
parameters (such as operational parameters) and/or control
signals which then operate in a lighting system to produce a
third waveform (as an instance of the resulting combination)
for the electrical biasing provided to the solid state lighting.
Any and all of these different representations or instantiations
may be considered a resulting combination or composite
waveform in accordance with the present disclosure.
[0014]
Reference to a parameter or parameters is also to be
the emitted spectrum, and such an emitted spectrum may
range from a quite narrow band (e.g., a single wavelength) to
construed broadly, and may mean and include coef?cients,
variables, operational parameters, a value stored in a memory,
a considerably broader band (a range of wavelengths),
or any other value or number which can be utilized to repre
Aug. 7, 2014
US 2014/0217915 A1
sent a signal, such as a time-varying signal. For example, one
less than one, and coef?cient “k2” is a ratio of averaged
or more parameters may be derived and stored in a memory
biasing voltage or current for wavelength compensation.
[0018] In another representative embodiment, the com
bined ?rst electrical biasing and second electrical biasing is
and utilized by a controller to generate a control signal, men
tioned above, for a lighting system which provides an elec
trical biasing having a third, combined waveform. Continuing
an alternation between the ?rst electrical biasing and second
with the example, in this instance the parameters may be
stored in memory and may represent information such as duty
electrical biasing. For example, the ?rst electrical biasing
may be pulse width modulation having a ?rst duty cycle lower
than a full intensity duty cycle and the second electrical
cycle, amplitude, time period or time interval, frequency,
duration, repetition interval or repetition period, other time
biasing may be constant current regulation having a ?rst
or interval-de?ned values, and so on, as discussed in greater
average current level lower than a full intensity current level.
detail below. For example, time-de?ned values of amplitude
The ?rst electrical biasing may be provided for a ?rst modu
lation period and the second electrical biasing may be pro
and duration are representative parameters, such as 100 mV
from the interval of 0 to l microseconds, followed by 200 mV
from the interval of l to 2 microseconds, followed by 0 mV
from the interval of 2 to 3 microseconds, which sequence may
then be repeated using a 3 microsecond repetition period, for
example, beginning with 100 mV from the interval of 3 to 4
microseconds, etc.
[0015] In a ?rst representative embodiment, the combined
?rst electrical biasing and second electrical biasing is a super
position of the ?rst electrical biasing and the second electrical
biasing. The superposition of the ?rst electrical biasing and
the second electrical biasing may be at least one predeter
mined parameter to produce the second emitted spectrum
within the predetermined variance for a selected intensity
level of a plurality of intensity levels. The combined ?rst
electrical biasing and second electrical biasing may comprise
a superposition of a symmetric or asymmetric AC signal on a
DC signal having an average component. The combined ?rst
electrical biasing and second electrical biasing may have a
duty cycle and an average current level, and the duty cycle and
the average current level may be parameters stored in a
memory and correspond to a selected intensity level of a
plurality of intensity levels.
[0016] In another representative embodiment, the com
bined ?rst electrical biasing and second electrical biasing
may be a superposition of or an alternation between at least
two of the following types of electrical biasing: pulse width
modulation, constant current regulation, pulse frequency
modulation; and pulse amplitude modulation.
[0017] In various representative embodiments, wherein the
combined ?rst electrical biasing and second electrical biasing
has a ?rst duty cycle ratio of peak electrical biasing, a second
duty cycle ratio of no forward biasing, and an average current
level, which are related to a selected intensity level according
to a ?rst relation of
vided for a second modulation period, which may be corre
sponding numbers of clock cycles. In representative
embodiments, the ?rst duty cycle, the ?rst average current
level, the ?rst modulation period, and the second modulation
period are predetermined parameters to produce the second
emitted spectrum within the predetermined variance for a
selected intensity level of a plurality of intensity levels.
[0019]
Generally, the combined ?rst electrical biasing and
second electrical biasing may be characterized as an asym
metric or symmetric AC signal with a positive average current
level. For example, a combined ?rst electrical biasing and
second electrical biasing may be pulse width modulation with
a peak current in a high state and an average current level at a
low state.
[0020] In another representative embodiment, the solid
state lighting comprises at least one light emitting diode
(“LED”), and the alternating ?rst electrical biasing and sec
ond electrical biasing are provided during at least one of the
following: within a single dimming cycle of a switch mode
LED driver, alternately every dimming cycle of the switch
mode LED driver, alternately every second dimming cycle of
the switch mode LED driver, alternately every third dimming
cycle of the switch mode LED driver, alternately an equal
number of consecutive dimming cycles of the switch mode
LED driver, or alternately an unequal number of consecutive
dimming cycles of the switch mode LED driver.
[0021] In various representative embodiments, the com
bined ?rst electrical biasing and second electrical biasing is
predetermined from a statistical characterization of the solid
state lighting in response to the ?rst electrical biasing and the
second electrical biasing at a plurality of intensity levels
and/or in response to a plurality of temperature levels. In
another representative embodiment, the combined ?rst elec
trical biasing and second electrical biasing is determined in
real time from at least one linear equation to produce the
second emitted spectrum within the predetermined variance
for a selected intensity level.
[0022]
and a second relation of
The representative method may also provide for
synchronizing the combined ?rst electrical biasing and sec
ond electrical biasing with a switching cycle of a switch mode
LED driver. For representative embodiments, the combined
?rst electrical biasing and second electrical biasing has a duty
cycle and an average current level which are related to a
selected intensity level according to a ?rst relation of
in which variable “d” is the ?rst duty cycle ratio, variable “0.”
is an amplitude modulation ratio corresponding to the ?rst
average current level, variable “D” is a dimming ratio corre
sponding to the selected intensity level, variable “[3” is the
second duty cycle ratio, coe?icient “kl” is a linear coef?cient
and a second relation of (FVDE, in which variable “d” is the
duty cycle, variable “0t” is an analog ratio corresponding to