JP2000023947A - Biological light measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a non-invasive measurement of biochemical components such as in-blood glucose density by providing a photodetector detecting light transmitting and diffusing in an organism and a circuit converting an output of the photodetector into voltage and sweeping frequency ranges which have prescribed values and are not zero by an oscillator. SOLUTION: Light made into monochrome by a slit 8 is introduced into an optical fiber 10-1 by a coupling lens 9 and an organism 11 is irradiated with light. In this case, a hand palm paddle is selected as a region to be measured of the organism 11 and any region easy to measure such as an ear lobe, fingers, arms may be selected. Light diffusing in the organism 11 is introduced into an optical fiber 10-2 by a lens 12 for collecting light and is made incident on a photodetector 13. The light detector 13 outputs photoelectric current proportional to light quantity and is converted into a voltage signal proportional to light quantity by a current voltage converter 14. Analog output voltage of the current voltage converter 14 becomes a digital signal by an A/D conversion board 16, a CPU 18 reads the digital signal via a bus and the digital signal is preserved in a RAM 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a predetermined part of a living body with light from the outside of a body by measuring the concentration of a chemical substance such as glucose, hemoglobin or cholesterol contained in a body fluid such as blood or tissue in a human body. The present invention relates to a technique for non-invasively measuring by detecting light emitted from a human body by transmitting or diffusing through a living body.

[0002]

2. Description of the Related Art An apparatus for non-invasively measuring a subject's blood glucose concentration (blood glucose level) by irradiating a human finger with near-infrared light and measuring the spectrum of the transmitted light has been developed. Chemistry, Vol. 38, No. 9, 1992,
It is described on pages 1618 to 1622. In the above-mentioned prior art, the output of a Fourier transform spectroscope using a tungsten halogen lamp as a light source or a dispersion type spectroscope that mechanically scans a diffraction grating is output to a subject's finger through an optical system constituted by a lens system or a fiber. And the transmitted light is condensed and detected from the side opposite to the irradiation side to obtain the near-infrared spectrum of the living body.

[0003]

In the prior art described above, the mechanical scanning of the optical element is performed in either the Fourier spectroscopy system or the dispersion spectroscopy system. As a result, it takes several seconds to measure the spectrum once. More time is essential. Therefore, the synchronization of the measurements at different wavelengths is not very good. Simultaneousness of each wavelength is important for correcting various fluctuations of a living body and baseline fluctuation of a spectrum by multi-wavelength measurement.

For example, if the living body moves a little, the measurement position shifts and the optical path length changes. The correction for the variation of the optical path length is 2
It is possible to take the ratio of the dimming degree of the wavelength, but if the measurement time of the dimming degree of the two wavelengths is before and after the body movement, the meaning is naturally lost. The time of a few seconds is a time that can be detected by a human, and is not always stationary.
Faster spectrum acquisition is desired.

[0005] Pulse wave spectroscopy is known as a method for improving the accuracy of spectroscopic measurement of a living body. This is a method of obtaining a highly accurate extinction degree of the blood itself by removing only a minute AC component synchronized with the pulsation from the extinction degree of the living body, thereby removing reflection on the skin surface, fluctuation of the measuring device, and the like.

At present, devices utilizing this principle use LEDs.
And multiple LDs are used to perform multi-wavelength measurement. In such a method, the synchronism of each wavelength is extremely good, but there is a problem in flexibility of wavelength selection and a large increase in the number of wavelengths. As a result, although the accuracy can be expected to be improved by increasing the number of wavelengths, the current apparatus based on pulse wave synchronization spectroscopy uses only a few wavelengths.

[0007] If the incandescent light source is spectrally separated, there are almost no restrictions on the wavelength and the number thereof. However, as described above, the spectrum measurement rate is not sufficient in the conventional technique of living body measurement using the incandescent lamp spectroscopy.

The human pulsation frequency is about 1.2 Hz at rest.
In order to measure a component that fluctuates at this frequency for the extinction of one wavelength, the sampling rate of the extinction must theoretically be at least twice as high as 1.2 Hz,
In practice, it is desirable to make it five times or more. Considering the rise of the pulsation frequency due to exercise and individual differences, it is practically recommended to be 10 times or more, that is, about 10 Hz or more.

[0009] In the mechanical scanning spectroscopy system, the highest speed model today has a limit of 5 spectral measurements per second, that is, a measurement rate of 5 Hz for the extinction of one fixed wavelength. Considering the balance with the accuracy, it is not expected that the mechanical scanning speed will be greatly improved in the future. In biological light measurement using the incandescent lamp spectroscopy, it is necessary to realize faster spectral measurement by a method other than mechanical scanning.

An object of the present invention is to perform a multi-wavelength spectrum measurement of a living body at a higher speed by an acousto-optic spectroscopic method.
It is to non-invasively measure the concentration of a light absorbing substance such as glucose, hemoglobin, bilirubin and the like in a living body with higher accuracy.

[0011]

An object of the present invention is to provide a light source having a broad emission spectrum, such as an incandescent lamp, by using an acousto-optic device to realize ultra-high-speed wavelength scanning and acquisition of one spectrum within a time of several tens of ms. Is achieved by doing

[0012]

FIG. 1 is a block diagram of a first embodiment of the present invention. 1 is a light source, 2 is a slit, 3 is a collimating lens, 4 is an acousto-optic element, 5 is an ultrasonic transducer, 6 is a power amplifier, 7 is a voltage controlled high-frequency oscillator, 8 is a slit, 9 is a coupling lens, 10 -1, 10-2 are optical fibers, 11 is a living body, 12 is a coupling lens, 1
Reference numeral 3 denotes a photodetector, 14 denotes a current-voltage converter, 15 denotes a computer housing, 16 denotes an AD conversion board, 17 denotes a DA conversion board, 18 denotes a central processing unit, 19 denotes a random access memory, and 20 denotes a display. The light source 1 in this embodiment is 2
This is a 00W tungsten halogen lamp. Of course, any light source having a broad emission spectrum having a half-value width of 10 nm or more including a necessary wavelength range may be used. For example, an organic electroluminescent material, a fluorescent material, a fluorescent lamp, a semiconductor light emitting device such as an LED or an SLD may be used.

The light emitted from the light source 1 is limited in solid angle by a slit 2 to improve spatial coherence, and then is converted into a parallel light beam by a lens 3 and is incident on an acousto-optic element 4. In this embodiment, chalcogenide glass is used as the acousto-optic medium. However, TeO ₂ , InP, LiNbO ₃ , and PbMo are used.
It is possible to arbitrarily use a material that is transparent in the near infrared region such as O ₄ and SiO ₂ and has a high acousto-optic figure of merit.

The high-frequency signal output from the voltage-controlled high-frequency oscillator 7 is amplified by the power amplifier 6 and is input to the ultrasonic transducer 5 bonded to the acousto-optic element 4. The ultrasonic transducer 5 generates an ultrasonic wave, that is, a diffraction grating having a density in the acousto-optic element 4, so that the white light of the light source 1 is diffracted. When the propagation direction of the ultrasonic wave is inclined by θ / 2 from the direction perpendicular to the incident light, the wavelength λ of the light diffracted in the θ direction, the sound velocity V of the acousto-optic element, and the frequency f of the ultrasonic wave Has the relationship of Equation 1.

[0015]

(Equation 1)

The light of the tungsten halogen lamp 1 includes light of a wide range of wavelengths from visible to infrared.
By extracting light of a constant θ, light of a specific wavelength is extracted. If the limit of θ due to the slit is Δθ, if θ is sufficiently small, the wavelength resolution Δλ and Δλ
Equation 2 holds between θ.

[0017]

(Equation 2)

In this embodiment, V = 2.52 × 10 ³ m / s,
Since the range of the frequency f was 94 to 109 MHz and θ = 70 mrad, the wavelength range was 1620 to 1870 nm and the resolution Δ
θ = 7 to 14 nm. The light monochromatized by the slit 8 is introduced into the optical fiber 10-1 by the coupling lens 9 and illuminates the living body 11. In this embodiment, the living body 1
Although the palm of a hand was selected as the measurement site in (1), it goes without saying that any site that can be easily measured, such as an earlobe, a crack, or an arm, may be used.

The light diffused in the living body is collected by a focusing lens 12.
Is introduced into the optical fiber 10-2 and is incident on the photodetector 13. The photodetector 13 outputs a photocurrent proportional to the amount of light, and this photocurrent is converted by a current-voltage converter 14 into a voltage signal proportional to the amount of light. The analog output voltage of the current / voltage converter 14 is converted into a digital signal by the AD conversion board 16 and is sent to a central processing unit (CPU) 18 via a bus.
Is read and stored in the random access memory (RAM) 19.

The AD conversion board 16 has a built-in sample hold circuit for sampling, and can perform sampling and AD conversion in synchronization with an external clock.
The output voltage of the DA conversion board 17 is input to the voltage-controlled high-frequency oscillator 7, and the oscillator 7 generates a signal having a frequency proportional to the input voltage. The central processing unit 18 is a DA
The output voltage of the conversion board is changed at predetermined steps within a certain range, and a signal of 94 to 109 MHz is output to the oscillator 7. As a result, the wavelength of the diffracted light is changed from 1620 nm to 186 nm.
Scan in 5 nm steps over a range of 5 nm. Both the sample rate and the output rate of the DA conversion board 17 and the AD conversion board are 5 kHz, and the voltage output of the DA and the voltage capture of the AD are synchronized. The number of wavelengths is 50
Because of the wavelength, 100 spectral measurements per second are possible.

In order for the movement of the living body to be negligible, 0.2
One spectrum may be obtained within a time period of less than one second, but in this embodiment, the measurement is performed at 0.01 seconds with a sufficient margin. The time required for one spectrum measurement is as short as 10 ms,
All wavelength measurements can be considered almost simultaneous. The voltage of AD is taken 0.1m from the voltage output of DA.
s to prevent wavelength errors during wavelength access.

At the start of the measurement, the living body 11 is first removed from FIG. 1, and the reference spectrum is measured with the optical fibers 10-1 and 10-2 connected directly.
Carried out as previously mentioned with respect to the wavelength scanning, the wavelength lambda _1, lambda _2, the voltage value V ₀ (λ ₁₎ corresponding to · · · lambda _N, V
₀ (λ ₂ ),... V ₀ (λ _N ) are stored in the memory 19. After that, the voltage values V (λ ₁ ), V (λ ₂ ),... V (λ _N ) corresponding to each wavelength are similarly measured in a state of being attached to the living body. The central processing unit controls the light attenuations A (λ ₁ ), A (λ ₂ ),
... A (λ _N ) is calculated according to Equation 3.

[0023]

(Equation 3)

In this way, the extinction spectrum becomes 10 per second.
Measured 0 times. In this embodiment, N = 50.

Next, data processing after the light attenuation measurement will be described with reference to FIG. Equation 4 is obtained as a column of the light attenuation spectrum obtained every 50 ms.

[0026]

Equation 4] _{{A 1 (λ 1),} A 1 (λ 2), ··· A 1 (λ N)}, {A 2 (λ 1), A 2 (λ 2), ··· A 2 (λ _N )},... (4) Each spectrum is first differentiated with respect to wavelength, and the number 5 of second derivative spectra with respect to wavelength is calculated.

[0027]

## EQU5 ## {D ₂ A ₁ (λ ₁ ), D ₂ A ₁ (λ ₂ ),... D ₂ A ₁ (λ _N )} (5) Next, an error due to the fluctuation of the optical path length is corrected. Therefore, the value of each secondary differential dimming value is divided by the value of the predetermined one wavelength λ _{M to} obtain a sequence of the specific dimming intensity spectrum. That is, Equation 6 is obtained.

[0028]

６D ₂ A ₁ (λ ₁ ) / D ₂ A ₁ (λ _M ), D ₂ A ₁ (λ ₂ ) / D ₂ A ₁ (λ _M ),..., D ₂ A ₁ (λ _N ) / D ₂ A ₁ (λ _M )｝ (6) In this embodiment, 1790 nm, which is less affected by temperature, was selected as the reference wavelength λ _M for obtaining the ratio. Since the value of the secondary differential ratio extinction spectrum is hardly affected by a statistical error due to body movement, random noise of the photodetector is dominant as noise. In order to reduce random noise, each value of the secondary differential ratio extinction spectrum is 1 for the same wavelength.
The values obtained every 0 ms are integrated.

In this embodiment, the integration is performed 500 times over 5 seconds. With these processes, extremely high-precision extinction measurement can be performed on a living body, and as a result, a change in the blood glucose concentration of 50 mg / dL in the living body can be detected with good reproducibility. In this embodiment, the dimming degree is differentiated with respect to the wavelength. However, it goes without saying that the same effect can be obtained by differentiating the wave number which is the reciprocal of the wavelength or the frequency of light which is proportional to the wave number.

In this embodiment, since the measurement object is glucose, the absorption band of glucose is 1600 nm.
Although a wavelength around m to 1850 nm was used, a change in the concentration of another substance can be similarly detected by scanning a wavelength range including the wavelength of the absorption band of the substance. For example, 700-900n for hemoglobin
What is necessary is just to include the wavelength band near m.

FIG. 3 is a block diagram of a second embodiment of the present invention. The second embodiment has basically the same configuration as the first embodiment, and the main changes are as follows.

In the present embodiment, the monochromatic light is not input to the optical fiber by the lens, but is reflected by the mirror 21 to irradiate the living body 11 as a beam in the space simply by preventing reflection loss to the fiber. In addition, light diffused in the living body is not captured by the fiber, and the light detector 13 is solidly attached to the living body 11, thereby increasing the light-collecting efficiency.

In this embodiment, the ultrasonic carrier signal output from the high frequency oscillator 7 is input to the radio frequency input of the modulator 25, and the modulation signal output from the low frequency oscillator 24 is input to the modulation input of the modulator 24. Then, the intensity of the ultrasonic waves generated in the acousto-optic element 4 is modulated.

The frequency of the low frequency oscillator 24 is sufficiently lower than the frequency of the high frequency signal which is a carrier.
00 kHz. As a result of the intensity modulation of the ultrasonic wave, the intensity of the diffracted light and the intensity of the light diffused in the living body become 500 kHz.
modulated by z. Therefore, the output of the detector 13 is the cable 2
After being converted into a voltage signal by the amplifier 14 connected in 2, the voltage signal is input to a lock-in amplifier synchronized with the output of the low frequency oscillator 24, and only the intensity modulation component of the signal is lock-in detected. For this reason, the light serving as the original signal is distinguished from the background light such as the light of the room light and the sunlight, and the measurement with the extremely small influence of the stray light is realized.

As a result of the above improvements, the efficiency, sensitivity and accuracy of light detection are greatly improved in the present embodiment, and the attenuation in the living body is large, so that the measurement was difficult in the first embodiment.
Measurement using light in the 2200-2300 nm band has become possible. In order to use the 2200-2300 nm band, in this embodiment, the frequency of the high-frequency carrier signal is 66 MHz to 6 MHz.
The frequency was set to 9 MHz and 50 wavelengths in 2 nm steps.

Next, the processing after the DC output of the lock-in amplifier is taken into the central processing unit and the memory 19 by the AD conversion board 16 will be described with reference to FIG. As in the first embodiment, the time series of the extinction spectrum of Expression 7 is obtained.

[0037]

Equation 7] _{{A 1 (λ 1),} A 1 (λ 2), ··· A 1 (λ N)}, {A 2 (λ 1), A 2 (λ 2), ··· A 2 (λ _N )｝,... (7) This is vertically divided into a series for each wavelength, and the time series of the extinction degree for each wavelength is represented by Expression 8.

[0038]

８A ₁ (λ ₁ ), A ₂ (λ ₁ ), A ₃ (λ ₁ ),..., ｛A ₁ (λ ₂ ), A ₂ (λ ₂ ), A ₃ (λ ₂ ),...,... (8) The central processing unit 18 obtains a component synchronized with the pulse of the living body 11 from the light attenuation time series for each wavelength sampled every 10 ms, more specifically, the frequency. Calculate Equation 9 in which the amplitude of the AC component of 0.85-1.7 Hz is smoothed with a predetermined time constant, and Equation 10 which is a DC component in which the original time series is simply smoothed with a predetermined time constant. Equation 1 which is the ratio of AC and DC components
Calculate 1.

[0039]

９B ₁ (λ ₁ ), B ₂ (λ ₁ ), B ₃ (λ ₁ ),..., ｛B ₁ (λ ₂ ), B ₂ (λ ₂ ), B ₃ (λ ₂ ), ・ ・ ・｝, ・ ・ ・… (9)

[0040]

１０C ₁ (λ ₁ ), C ₂ (λ ₁ ), C ₃ (λ ₁ ),..., ｛C ₁ (λ ₂ ), C ₂ (λ ₂ ), C ₃ (λ ₂ ), ...｝… (10)

[0041]

{B ₁ (λ ₁ ) / C ₁ (λ ₁ ), B ₂ (λ ₁ ) / C ₂ (λ ₁ ), B ₃ (λ ₁ ) / C ₃ (λ ₁ ),. }, {B ₁ (λ ₂ ) / C ₁ (λ ₂ ), B ₂ (λ ₂ ) / C ₂ (λ ₂ ), B ₃ (λ ₂ ) / C ₃ (λ ₂ ),. (11) The time series of this ratio for each wavelength is represented by Equation 12.

[0042]

１２D ₁ (λ ₁ ), D ₂ (λ ₁ ), D ₃ (λ ₁ ),..., ΔD ₁ (λ ₂ ), D ₂ (λ ₂ ), D ₃ (λ ₂ ),...,... (12) Further, the central processing unit divides each series of D values based on a predetermined value of one wavelength λ _M to obtain the number of ratio spectra 13 for the pulsation component. Here, λ _M = 2250 nm.

[0043]

１３D ₁ (λ _i ) / D ₁ (λ _M ), D ₂ (λ _i ) / D ₁ (λ _M ), D ₃ (λ _i ) / D ₁ (λ _M ),. ｝ (Where i = 1, 2,... N) (13) The value of this ratio spectrum has few individual differences, and enables a more accurate measurement of the biological extinction than the first embodiment. In the example, glucose absorption is large 2200-230
Since the 0-nm band is used and the pulsating component is further extracted, the glucose concentration in blood can be measured with an error of 10 mg / dL.

In this embodiment, the spectrum measurement rate is set to 100 Hz, which is much higher than the frequency of human pulsation. However, if the subject is in a resting state, the pulse rate is 2H.
Since it is equal to or less than z, the pulsation component can be similarly detected at a spectrum measurement rate of 5 Hz or more. In that case, the number of wavelengths to be scanned can be increased, so that higher reliability can be obtained.

[0045]

According to the present invention, it is possible to irradiate a living body with light having several tens of wavelengths or more almost at the same time in living body light measurement, thereby realizing ultra-multi-wavelength spectrum measurement with high synchronism. For this reason, a highly accurate measurement of the biological extinction degree becomes possible, and as a result, non-invasive measurement of biochemical components such as blood glucose concentration becomes possible.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing the configuration of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a signal processing process according to the first embodiment of the present invention.

FIG. 3 is a conceptual diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a signal processing process according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... light source, 2 ... slit, 3 ... collimating lens, 4 ...
Acousto-optic element, 5: ultrasonic transducer, 6: power amplifier, 7
... voltage controlled high frequency oscillator, 8 ... slit, 9 ... coupling lens, 10-1, 10-2 ... optical fiber, 11
... living body, 12 ... coupling lens, 13 ... photodetector,
14 ... current-voltage converter, 15 ... computer housing, 16
... AD conversion board, 17 ... DA conversion board, 18 ... Central processing unit, 19 ... Random access memory, 20 ... Display, 21 ... Mirror, 22 ... Cable, 23 ... Lock-in amplifier, 24 ... Low frequency oscillator, 25 ... Modulator.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masao Kan 1-280 Higashi Koigakubo, Kokubunji, Tokyo, Japan Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Takeshi Ken Ninomiya 1-280 Higashi Koigakubo, Kokubunji, Tokyo, Hitachi, Ltd. Central Research Laboratory F-term (reference) 2G045 AA13 AA16 CA25 CB03 DA31 DA51 FA03 FA11 FA29 FA32 FA34 JA01 2G047 AA04 AC13 CA01 EA00 2G059 AA06 BB13 CC18 EE01 EE12 GG02 HH01 HH06 JJ05 JJ13 KM10 MM10 MM01 MM01 MM10 MM10

Claims (7)

[Claims] 1. A light source having an emission spectrum half width of 10 nm or more, a medium fixed to the light source and transparent to near-infrared light, A sound wave transducer, a frequency-sweepable oscillator that supplies a high-frequency signal to the transducer via the electrode, a wavefront of light transmitted through the medium, a slit whose position is fixed relative to the medium, An optical system for irradiating the living body with light transmitted through the slit, a photodetector for detecting light transmitted or diffused in the living body, and a circuit for converting the output of the photodetector to a voltage, wherein the oscillator is a predetermined type A biological light measurement method characterized by sweeping a non-zero frequency range. 2. A light source having an emission spectrum half width of 10 nm or more, a medium fixed to the light source and transparent to near-infrared light, An acoustic transducer, a frequency-sweepable oscillator that supplies a high-frequency signal to the transducer via the electrode, a wavefront of light transmitted through the medium, a slit whose position is fixed relative to the medium, An optical system that irradiates a living body with light transmitted through the slit, a photodetector that detects light transmitted or diffused in the living body, and an impedance conversion circuit that converts an output of the photodetector into a voltage corresponding to a detected light amount And an AD conversion circuit that samples and holds the output voltage of the circuit and converts the output voltage into a digital signal, and performs calculation using the digital signal output from the AD conversion circuit. A processing device, wherein the oscillator sweeps a predetermined non-zero frequency range in less than 0.2 seconds, and the AD conversion is performed at a moment when the frequency of the output signal of the oscillator is at a plurality of predetermined points in the frequency sweep range. The circuit performs A / D conversion to output a digital signal, and the central processing unit
A biological light measurement method, wherein a calculation is performed between a plurality of digital signals in which the time when the D conversion is performed is within 0.2 seconds. 3. A light source having an emission spectrum half width of 10 nm or more, a medium fixed to the light source and transparent to near-infrared light, and a superconducting medium in surface contact with the medium and having an electrode. A sound wave transducer, a frequency-sweepable oscillator that supplies a high-frequency signal to the transducer via the electrode, a wavefront of light transmitted through the medium, a slit whose position is fixed relative to the medium, An optical system that irradiates a living body with light transmitted through the slit, a photodetector that detects light transmitted or diffused in the living body, and an impedance conversion circuit that converts an output of the photodetector into a voltage corresponding to a detected light amount An AD conversion circuit that samples and holds the output voltage of the circuit and converts the output voltage into a digital signal; and performing calculation using the digital signal output from the AD conversion circuit. A processing device, wherein the oscillator repeatedly sweeps a predetermined non-zero frequency range at a predetermined frequency of 5 times or more per second, and when the frequency of the output signal of the oscillator is at a plurality of predetermined frequencies within the frequency sweep range. The A / D conversion circuit performs A / D conversion to output a digital signal, and the central processing unit calculates the dimming degree of the living body at the time when the digital signal is obtained. Based on the time series of the dimming degree obtained at the predetermined frequency in which the frequency of the output signal is the same, the central processing unit calculates the amplitude of the AC component of the dimming degree synchronized with the pulse of the living body. A biological light measurement method, characterized in that: 4. A method for measuring biological light, wherein the medium according to claim 1 is chalcogenide glass. 5. The calculation method according to claim 2, wherein the calculation of the dimming degree using the digital signal obtained by one sweep and the calculation of each dimming degree of the dimming degree are performed. Differentiation as a function of the wavelength or the wave number of light irradiated to the living body at the moment when the signal is obtained, and calculation of the ratio between a plurality of values obtained by differentiation and a value corresponding to one specific wavelength. A biological light measurement method, characterized in that: 6. The output of the high-frequency oscillator according to claim 1 is amplitude-modulated by the output signal of the low-frequency oscillator, and then input to the ultrasonic transducer, and the output voltage of the circuit is synchronized with the output of the low-frequency oscillator. A biological light measurement method, wherein lock-in detection is performed. 7. A biological light measurement method according to claim 1, wherein said light source is a tungsten halogen lamp.