Abstract: It is the task of the present invention to provide an LED lighting device that is adapted for an AC voltage supply. Suggested for that is an LED lighting device 1 for an AC voltage supply 2, with several LEDs that form a whole chain 9, whereby the LEDs are divided into LED part groups 11 a, b, c, d, x, y, whereby a supply voltage with changing amplitude is present in the LED lighting device 1, and with several serial switching means 12a, b, c, d, x, y, and with several shorting links 16a, b, and with a control means 10, whereby the control means 10 is designed for controlling the shorting links 16a, b, and the serial switching means 12a, b, c, d, x, y in order to place the whole chain 9 in at least two switch states 1,11, whereby the at least two switch states 1,11 differ in the through voltage of the whole chain 9.

Abstract: A lighting control system includes a plurality of luminaires each having a selectively powerable first light source and a selectively powerable second light source. The luminaires are powerable and controllable by a common AC power source. A signal receiving controller of each of the luminaires is electrically connected to the first light source and the second light source and selectively causes power to be routed to either the first light source or the second light source dependent on a control signal sent via the AC power source.

Abstract: Driver circuits (20) for driving light circuits (21) comprising light emitting diodes are provided with converters (22) for converting input signals into output signals comprising pulses per cycle. The converters (22) comprise adapters (33) for, in response to differences between measured amplitude values of the input/output signals and nominal amplitude values of the input/output signals, adapting widths of the pulses. Then, signals having relatively precise amplitudes are no longer required. Said adapting may comprise increasing/decreasing the widths in case the measured amplitude value is smaller/larger, respectively, than the nominal amplitude value. The measured amplitude value divided by the nominal amplitude value is equal to a correction value. An adjusted duty cycle of the output signal may be made equal to a nominal duty cycle of the output signal divided by the correction value. Said adapting may be performed in a production/testing process environment.

Abstract: A first LED group including a plurality of LEDs is regularly arranged in a toric shape on the circumference of a center of an approximately rectangular substrate which is formed of ceramics. In addition, the first LED group including the plurality of LEDs is entirely covered in a toric shape with a sealing member. In addition, a second LED group including a plurality of LEDs is regularly arranged in a grid shape in the vicinity of the center of the approximately rectangular substrate. In addition, the LED group including the plurality of LEDs is entirely covered with a sealing member. In addition, the sealing member entirely covers the inside of the toric portion of a first region.

Abstract: A method includes receiving a sense signal having multiple pulses, where the sense signal is based on an output of a dimmer. The method also includes, for each of multiple sampling periods, sampling a subset of the pulses in the sense signal during that sampling period. The method further includes generating a holding current for the dimmer during the sampling of the subset of pulses in at least one of the sampling periods. In addition, the method includes, for each of the sampling periods, generating an output value identifying a duty cycle for driving one or more light emitting diodes (LEDs). The subset of pulses in each of the sampling periods includes multiple pulses during that sampling period but not one or more initial pulses at a beginning of that sampling period.

Abstract: A luminaire includes a primary HID light source housing having at least one selectively powerable HID lamp and an LED arm assembly having a secondary LED light source. In some embodiments the LED arm assembly may extend between a support structure and the HID light source housing and in other embodiments the LED arm assembly may be a stand alone assembly and extend from a support structure remote from the HID light source housing. The HID lamp may be powered during user selected peak hours and the LED light source may be powered during user selected non-peak hours.

Abstract: An LED lighting system includes a power supply module, a data input line routed through the power supply module, an AC power input, and an LED fixture. The power supply module includes a power supply unit and an AC power cable. The AC power input is electrically connected to the power supply unit and the AC power cable. The LED fixture is electrically connected to an output of the power supply unit and the data input cable, and includes one or more LED assemblies disposed on a circuit board, a data signal output, and a power output. The AC power cable may be routed through the LED fixture.

Abstract: An Alternate Current (AC) white Light-Emitting Diode (LED) device is provided, which belongs to the technical field of white LED manufacturing. The problem to be solved by the present invention is to low-costly overcome a series of deficiencies such as the stroboflash of an AC driven LED, and the heat dissipation difficulty caused by an integrated packaging of multiple LEDs. A white LED unit includes an LED chip and a light emitting material that can emit light when being excited by the LED chip. The luminous lifetime of the light emitting material is 1-100 ms. The LED chip only comprises one PN junction. The light emitted by the LED chip is mixed with the light emitted by the light emitting material to form white light. The white LED unit is driven by AC with a frequency not more than 100 Hz. The white LED device of prevent invention uses the single PN junction chip, rather than the prior integrated packaged AC multi-LED chip.

Abstract: Various embodiments of the invention allow for active AC ripple noise cancellation. In certain embodiments, noise cancellation is accomplished by modulating an LED driver output in a polarity opposite to the ripple, thereby, preventing interference with ripple-sensitive loads. Certain embodiments take advantage of a filter network to prevent the LED driver from modulating LED current in response to ripple that falls within a visible frequency range so as to prevent flicker in an LED backlight display. In addition to protecting ripple-sensitive loads from large ripple currents, efficiency is increased by reducing both I2·R losses and peak currents, thereby, extending the useful battery life time in mobile devices.

Abstract: An approach is provided for a method that minimizes stroboscopic effects in PWM driven lighting, which comprises acts of generating at least two enabling signals that drive at least one corresponding lamp, adjusting widths of pulses of each enabling signal corresponding to specific timestamps by a predetermined rule, and forming an overall brightness output in response to the superposition of the enabling signals. Each enabling signal is synchronized to an input power of the lamp. The method of the present invention makes light from lamps using multiple phases that significantly minimize stroboscopic effect.

Abstract: A light emitting device and the fabrication method includes forming one or more light emitting modules on a substrate. The light emitting module receives an alternating current input and has at least two micro diodes. Each micro diode has at least two active layers and is electrically connected by a conductive structure so as to allow the active layers of the micro diodes to alternately emit light during positive and negative cycles of the alternating-current input.

Abstract: A controller for a light fixture includes: a current-sampling circuit adapted to be connected electrically to the light fixture, and operable to generate a voltage signal corresponding to a current flowing through a light source of the light fixture; a voltage-processing circuit operable to perform at least one of voltage-amplification and voltage-rectification processes upon the voltage signal so as to generate a recognition signal; a signal-recognition unit configured to generate a control signal according to the recognition signal; a driver unit operable to generate a driver signal corresponding to the control signal; and a driving component adapted to be connected electrically to the light fixture, and driven by the driver signal for controlling operation of the light source of the light fixture.

Abstract: Disclosed is a method for controlling a lighting apparatus comprising a first light source unit, a second light source unit and a third light source unit, all of which emit lights having mutually different color temperatures and mutually different color coordinates, the method comprising: outputting an R component signal, a G component signal and a B component signal, each of which respectively corresponds to light quantities of an R component, a G component and a B component of lights outputted from the first light source unit, the second light source unit and the third light source unit; receiving the R component signal, the G component signal and the B component signal and generating a comparative color coordinate; and comparing the comparative color coordinate with standard color coordinates located within an area formed by the respective color coordinates of the first, the second and the third light source units, and controlling light quantities of the first, the second and the third light source units i

Abstract: A luminary dimming system having a three terminal dimming unit. The dimming unit includes a power controller and a receiver and is responsive to dimming directives received by the receiver. The power controller controls a buck switch and a freewheel switch in a manner that allows reduction of alternating current voltages. Such voltage reduction is accomplished in a manner that preserves the waveform of the source voltage and the power factor exhibited by the luminary.

Abstract: A lighting system for sports equipment is disclosed that includes one or more color-emitting light sources, which can be, for example, red-green-blue light-emitting diodes or flexible video displays, and a computer-based controller configured to vary emissions of said light sources. The sports equipment may be a snow board, snow skis, a skate board, water skis, and a wake board.

Abstract: A multi-phase lighting driver.

Abstract: A modular light emitting apparatus includes a light emitting device, a connector to couple to an AC power source, circuitry on a first electronics module to drive the light emitting device, and a support structure arranged to position and hold a second electronics module that conforms to a predetermined form factor.

Abstract: A lighting apparatus includes a light emitting device that has an attribute that is adjustable responsive to a control signal carried on a power line from which the light emitting device receives an Alternating Current (AC) power signal.

Abstract: A method for controlling a lighting current of a lighting device with a number of semiconductor lighting means, installed for signaling and marking traffic areas of airports, in which period intervals are predetermined with a fixed period length, selected with an average lighting current to operate a semiconductor lighting means within the period intervals and in each of the period intervals a number of current pulses is generated with a pulse amplitude IP and a fixed pulse duration T, with the number of current pulses in each period interval being selected such that within the period intervals the respectively predetermined average lighting current is reached, with the pulse pauses being variably adjusted between subsequent current pulses.

Abstract: In a method for operating at least one light emitting diode the at least one light emitting diode is operated at least in some ranges by means of a pulse number modulation, in which a number of uniform current pulses is set within a predetermined interval duration depending on a light energy desired value.

Abstract: An illumination source for a camera includes one or more LEDs, and an electrical circuit that selectively applies power from the DC voltage source to the LEDs, wherein the illumination source is suitable for handheld portable operation. In some embodiments, the electrical circuit further includes a control circuit for driving the LEDs with electrical pulses at a frequency high enough that light produced has an appearance to a human user of being continuous rather than pulsed, the control circuit changing a pulse characteristic to adjust a proportion of light output having the first characteristic color spectrum output to that having the second characteristic color spectrum output. Some embodiments provide an illumination source including a housing including one or more LEDs; and a control circuit that selectively applies power from a source of electric power to the LEDs, thus controlling a light output color spectrum of the LEDs.

Abstract: An LED lighting apparatus includes a triac dimmer 3, a series circuit connected to the triac dimmer and including a primary winding P of a switching transformer T and a switching element Q1, the switching transformer having a plurality of windings, a controller 14 of the switching element, a rectifying-smoothing circuit of a voltage of a secondary winding S of the switching transformer, LEDs 1a to 1n connected to an output of the rectifying-smoothing circuit, a current detector 7 detecting a current of the, a voltage detector 11 configured to output a voltage detection signal of a voltage generated at one of the secondary winding when the first rectifying element is ON, the voltage at the secondary winding being proportional to the phase-controlled AC voltage, and an amplifier 13 amplifying a signal that is based on the current detection signal and voltage detection signal for the controller.

Abstract: A light-emitting-element lighting circuit for dimming a light emitting element by a PWM dimming signal of a duty ratio corresponding to an input dimming signal is provided. The lighting circuit includes a PWM dimming signal generating unit which generates the PWM dimming signal by performing a summation of AC wave signals including a fundamental wave and harmonics of different frequencies that are integer multiples of a fundamental frequency of the fundamental wave. The fundamental frequency is equal to or higher than a frequency, at which a sound pressure level is at maximum, in an audible frequency range in a correlation spectrum between the sound pressure level generated from the light emitting element and a frequency of an AC wave signal inputted to the light emitting element.

Abstract: Emission systems having solid-state transducers (SSTs) for producing a target chromaticity of light are disclosed herein. An emission system or SST device in accordance with a particular embodiment can include a first emitter having a first plurality of SSTs positioned to emit light having a first chromaticity, and a second emitter having a second plurality of SSTs positioned to emit light having a second chromaticity different than the first chromaticity. The SST device can further include a controller having a first channel with a variable output, coupled to the first emitter to adjust the brightness level of the first emitter, and a second channel with a variable output, coupled to the second emitter to adjust the brightness level of the second emitter.

Abstract: A solid-state lighting system comprises a plurality of light-emitting devices (e.g., light-emitting diodes) and an alternating current to direct current (AC-DC) converter that converts AC power to DC power for powering the plurality of light-emitting devices. The AC-DC converter is configured to perform AC-DC conversion directly, without the need for or use of a bridge rectifier or step-down transformer. According to one aspect of the invention, the light-emitting devices of the solid-state lighting system are autonomous and individually powered by a plurality of DC power supplies generated from the DC power produced by the AC-DC converter. According to another aspect, a plurality of phase-offset dimmer control signals are generated based on waveform distortions in a dimming signal produced by a conventional dimmer switch. The phase-offset dimmer control signals are used to individually control the dimming of the light-emitting devices.

Abstract: A device and a method for driving a light-emitting diode include using multiple current guiding control circuits to drive multiple LED modules. Each of the current guiding control circuits includes at least two transistors connected in parallel to constitute at least two switch circuits. Each of the current guiding control circuits permits or prevents electric current to flow to an immediate downstream one of the LED modules in response to a predetermined voltage level of the positive part of a voltage source. The respective the current guiding control circuits are responsive to different voltage levels. As a result, a maximum number of LED modules are driven to emit light at a given voltage level, thereby achieving the purposes of efficiently utilizing electric power and reducing power loss.

Abstract: A remote directs illumination of an illumination source according to a duty cycle. The duty cycle defines a first portion of time power is provided from a battery and a second portion of time power is not provided. The remote monitors voltage output by the battery and adjusts the duty cycle to increase the duration of the first portion based on a decrease of the monitored voltage compared to a maximum voltage level. The remote may adjust the duty cycle in order to maintain a consistent illumination output level. In some implementations, the remote may adjust the duty cycle based on one or more threshold values. In other implementations, the remote may adjust the duty cycle directly based on the measured voltage. In still other implementations, the remote may not calculate the duty cycle directly but may instead reference a lookup table.

Abstract: An LED driving device includes: an LED circuit having an input side for receiving a driving current corresponding to an AC input voltage from an external power source when the magnitude of a driving voltage across the input side is greater than a predetermined value; and a clamp circuit coupled between the input side of the LED circuit and the external power source, and permitting the driving current to pass through for clamping the magnitude of the driving current to a predetermined current level and for clamping the magnitude of the driving voltage to a predetermined voltage level.

Abstract: The invention relates to a driving circuit comprising a first bridge circuit, a second bridge circuit, a first protection device and a second protection device. The first bridge circuit comprising a first positive input terminal, a first negative input terminal, a first positive output terminal and a first negative output terminal is coupled to an AC voltage source to output a first voltage. The second bridge circuit comprising a second positive input terminal, a second negative input terminal, a second positive output terminal and a second negative output terminal is coupled to the AC voltage source to output a second voltage. The second and the first negative output terminals are both coupled to the ground potential. The first protection device is coupled between the second positive input terminal and the AC voltage source. The second protection device is coupled between the second negative input terminal and the AC voltage source.

Abstract: A portable lighting system including a housing having an elongated slot formed in a surface of the housing. The slot being sized to receive a rod therein via an opening in the slot. The system further including a retention member movable between a closed position and an opened position, wherein the closed position provides at least a portion of the retention member blocking at least a portion of the upper opening of the slot and the opened position includes the retention member not blocking the upper opening of the slot. The system also having a light source including a plurality of lights oriented in different directions.

Abstract: A lamp with a base (1) and at least one light emitting semiconductor component (2) is disclosed. The base has at least two external electrical connections (11, 12) and at least two electrical connection parts (13, 14). The electrical connection parts are provided for electrically connecting the light emitting semiconductor component and are respectively connected to one of the external electrical connections in an electrically conducting manner. The light emitting semiconductor component is mounted on a carrier (3) and is electrically connected to at least two electrical contacting elements (31, 32), which are arranged and/or fixed on the carrier. Each of the electrical contacting elements is directly adjacent to one of the electrical connection parts and connected to it in an electrically conducting manner.

Abstract: An appliance includes a cabinet, a solid state lighting device assembly integrated in the cabinet, and a power controller coupled to the solid state lighting device assembly for supplying electrical power to the solid state lighting device lighting assembly. The power controller is configured to provide a pulse modulated power signal to the solid state lighting device assembly that has a duty cycle. Each solid state lighting device in the solid state lighting device assembly cycles on and off in accordance with duty cycle.

Abstract: The present invention relates to methods for LED driver applications, comprising the steps: providing an input voltage, Vin; generating an output voltage, Vout, for driving a plurality of LED channels, wherein a boost converter is used to convert the input voltage Vin to the output voltage Vout; determining a lowest voltage, VLVS, from the LED channels; generating a comparator voltage, Vcomp, by comparing the lowest voltage of the channels, VLVS, with a feedback reference voltage, VFBREF, wherein the feedback reference voltage, VFBREF, and a LED current, ILED, for the LED channels are determined by a current ISET; generating a summed voltage, Vsum, for stabilizing the output voltage, Vout; and generating a PWM voltage, VPWM, as a function of the Vcomp and the Vsum to control the output voltage, Vout.

Abstract: In one embodiment, a light dimming module is disclosed. The light dimming module has a dimming engine coupled to a digital input interface and an output interface. The dimming engine is configured to provide a N-segment piecewise linear exponential digital control signal, and the output interface is configured to control the intensity of a light source.

Abstract: A light-emitting diode (LED) driver provides faster rise and fall times for LED current to reduce image sticking and other interference. A standard DC-DC converter provides a sum current that is slowly ramped up and down by a bypass current digital-to-analog converter (DAC). A digital value to the bypass current DAC is ramped up or down before an LED current is turned on or off. When the LED current is turned on, current is shifted from a bypass path to a path through the LED, maintaining a constant sum current from the DC-DC converter. When a different LED is turned on, current is shifted from one LED's path to the other LED's path. Separate LED current DAC's in each LED path and in the bypass path can share the sum current with digital precision. Using a single DAC for the sum current and switches in each path reduces cost.

Abstract: A ballast and method are presented for detecting end-of-life conditions of fluorescent lamps in which a ballast output is controlled according to a dimming input when a DC voltage or current of the lamp is in a predefined range or when the AC lamp current is below a predefined threshold, and the output is reduced to an EOL protection level when the lamp DC voltage or current is outside the predefined range and the AC lamp current is above the predefined threshold.

Abstract: What is proposed is: an operating device for operating in particular a light-emitting means (12), having: —supply terminals (16, 17) for connecting the operating device to a supply voltage provided by a supply source (20), —output terminals (10) for controlling the light-emitting means (12), —an interface (21) for connection to a bus (2), and—a transmission path which is coupled to the interface (21), wherein the transmission path is designed to connect the received supply voltage to the bus (2) selectively.

Abstract: An alternating current light emitting diode device is disclosed, which comprises a substrate having a supporting surface and two supporting elements locating on the two sides of the supporting surface; a plurality of LED grains set on the supporting surface; a first chip resistor set on one of the two supporting elements; and a plurality of electrical wires providing electrical connections between the LED grains, and between the LED grain and the first chip resistor. Therefore, the total wattage of the AC LED device can be lowered to a designed range by using a chip resistor with proper resistance, and the total illumination efficiency can be increased.

Abstract: A metal line 731 is formed in a linear area S of an insulative substrate 720, and moreover a metal line 732 is formed generally parallel to the metal line 731 with a specified distance thereto. The metal line 731 is connected to an n-type semiconductor core 701 of bar-like structure light-emitting elements 710A to 710D, and the metal line 732 is connected to a p-type semiconductor layer 702. By dividing the insulative substrate 720 into a plurality of divisional substrates, a plurality of light-emitting devices in each of which a plurality of bar-like structure light-emitting elements 710 are placed on the divisional substrates are formed.

Abstract: A light source apparatus includes a discharge lamp including a light-emitting container having a cavity in which a discharge medium is enclosed, and a pair of electrodes disposed such that respective tip portions thereof oppose each other in the cavity, and a driving unit that supplies a driving current to the pair of electrodes. The driving current is generated by modulating amplitude of alternating current having a frequency not lower than 1 kHz and not higher than 10 GHz, such that a first section and a second section in which the amplitude is smaller than in the first section are alternately repeated.

Abstract: The present invention has the object of suppressing variations of luminance and chromaticity among a plurality of organic EL elements. An illumination device includes: a plurality of organic EL elements; an operation unit that receives, for each organic EL element, chromaticity information that indicates chromaticity of the relevant organic EL element and luminance information that indicates the luminance of the relevant organic EL element; and a supply unit that, for each of the organic EL elements, supplies to an organic EL element a drive signal having amplitude that accords with the chromaticity indicated by the chromaticity information for that organic EL element for, within a unit time interval, a time interval that accords with luminance indicated by the luminance information for that organic EL element.

Abstract: A pulse width modulation (PWM) dimming circuit comprises a switch unit, a current generation unit, a mirror current source, a multi-path output unit, a plurality of current balance units and a plurality of LED lamp strings. The switch unit receives a PWM signal which controls the switch on or off. The current generation unit is connected with the switch unit and generates a current of a predetermined magnitude when the switch unit is on. The mirror current source is connected with the current generation unit and receives the current to generate a mirror current. The multi-path output unit is connected with the mirror current source and receives and output the mirror current in multiple paths. The current balance units are connected between the multi-path output unit and the LED lamp strings respectively. The PWM dimming circuit decreases both the difficulty and the manufacturing cost and is easy to operate.

Abstract: In various embodiments, a circuit arrangement for operating a series circuit of a first and a second low-pressure gas-discharge lamp is provided, which may include an input with a first and a second input connection for application of a supply voltage; an output with a first arrangement, which has a first and a second connection pair for connection of the first lamp, and a second arrangement, which has a first and a second connection pair for connection of the second lamp, wherein a first connection of the second pair of the first arrangement is coupled to a first connection of the first pair of the second arrangement; a resonant circuit; and a capacitive voltage divider, which has a first capacitor, which is coupled in parallel with the first arrangement, and a second capacitor, which is coupled in parallel with the second arrangement.

Abstract: A low THD lighting system is disclosed. The lighting system includes a first lighting module and a second lighting module connected parallel to the first lighting module. During each AC cycle the first lighting module conducts current for a first portion of the cycle and the second lighting module conducts current for a second portion of the cycle. When combined, the total current drawn from the power source substantially tracks the shape of the applied AC voltage. Accordingly, there is minimal distortion, and low total harmonic distortion level is achieved.

Abstract: A white light emitting apparatus includes a light source section in which a first white LED that emits white light whose chromaticity deviates to a blue side from a predetermined white region of a CIE chromaticity diagram and a second white LED that emits white light whose chromaticity deviates to a yellow side from the predetermined white region are adjacently disposed so as to emit light with optical axes in substantially the same direction, and a current regulator that independently drives the blue LED chip in the first and second white LEDs, respectively. A color mixture of lights emitted from the first and second white LEDs is adjusted to a chromaticity of the predetermined white region using the current regulator.

Abstract: A system includes multiple dynamic current equalizers (DCEs). Each DCE includes a first control loop configured to regulate a current through a circuit branch associated with the dynamic current equalizer. The first control loop includes a first amplifier having two inputs. Each DCE also includes a second control loop configured to regulate a control signal. The second control loop includes a second amplifier having two inputs coupled to the inputs of the first amplifier. The first amplifier has an input offset compared to the second amplifier. The DCEs are configured such that one DCE regulates the control signal while one or more other DCEs regulate the currents through the associated circuit branches based on the control signal. The DCEs can be configured to achieve one or more ratios between multiple currents flowing through multiple circuit branches, where the one or more ratios are defined by resistances coupled to the DCEs.

Abstract: Disclosed is a backlight apparatus comprising a plurality of light sources; and a control unit which drives the plurality of light sources at an identical driving frequency and which performs pulse-width modulation control for a turned-on period and a turned-off period of each of the light sources; wherein the control unit is capable of setting a duty ratio for each of the light sources and each of driving cycles; and the control unit sets the duty ratio for at least two of the light sources respectively so that a condition, in which one cycle period composed of one turned-on period and one turned-off period is N times the driving cycle, is fulfilled, and the duty ratio is 0 or 1 in at least one driving cycle of N pieces of the driving cycles for constructing the one cycle period if N is not less than 2.

Abstract: Disclosed is an illumination controller for use with at least one three-color LED module. The illumination controller includes a command input, three color control outputs, and a processor. The command input receives a unitary illumination control command having first, second and third color level values, and a fade rate value. First, second, and third color control outputs pulse modulates respective first, second and third signals that powers an illumination level for each color. The processor, responsive to a control command, transitions the first color control output in accordance with the received command's first color level value and the fade rate value, transitions the second color control output in accordance with the received command's second color level value and the fade rate value, and transitions the third color control output in accordance with the received command's third color level value and the fade rate value. The three colors may be red, green, and blue.

Abstract: To a constant-current power supply whose output current can be variably set, light emitting modules can be connected in parallel. A control unit recognizes connection information outputted from an information output unit provided in each of the light emitting modules and varies the output current of the constant-current power supply. Drive can be controlled in response to a state of the connected light emitting modules such as the connecting number of light emitting modules.

Abstract: Perceived output color and intensity (brightness) of light from a three-element red-green-blue (RGB) light emitting diode (LED) or optical combination of three LEDs (red, green and blue) are controlled with three pulse train signals, each having fixed pulse width and voltage amplitude and then increasing or decreasing the frequency (increasing or decreasing the number of pulses over a time period) of these pulse train signals so as to vary the average current through each of the RGB-LEDs. This reduces the level of electro-magnetic interference (EMI) at any one frequency by varying the pulse train energy spectrum over a plurality of frequencies.