NL1041760B1

NL1041760B1 - LED-lamp producing a daylight spectrum

Info

Publication number: NL1041760B1
Application number: NL1041760A
Authority: NL
Inventors: Johannes Van Og Marinus; Ir Sander Willem Hogewoning Dr
Original assignee: Specialty Lighting Holland Ip B V; Ir Sander Willem Hogewoning Dr
Priority date: 2016-03-11
Filing date: 2016-03-11
Publication date: 2017-09-27

Abstract

The present invention relates to an LED-based light source producing light with a spectral composition similar to that of natural daylight. The similarity of the spectrum produced by this light source with natural daylight is limited to the spectral range well visible to the human eye, i.e. 400-700 nm, or slightly beyond. The present invention is particularly useful for scientific research (plant sciences in particular), horticulture, and medical applications. Furthermore, present invention is useful for general applications where light with a natural spectral composition is desired under conditions where natural daylight is absent, or nearly absent (e.g. showrooms, hangars, etc.).

Description

Patent application for Invention: LED-lamp producing a daylight spectrum

Background of the invention

Sunlight reaching the Earth's surface is comprised of a broadband wavelength range within a range of approximately 300-2500 nm. Within this broad range of wavelengths, the spectral range between 400 nm and 700 nm, or slightly beyond, is well visible to the human eye. This is also the wavelength range that is important for driving photosynthesis in green plants, in which the irradiance supplies the energy for the conversion of C02 and water into sugars and oxygen. Therefore, this wavelength range is vital for food production, and C02 depletion from and supply of oxygen to the Earth's atmosphere. Therefore the wavelength range 400-700nm is also called Photosynthetically Active Radiation (PAR). For plants, wavelengths slightly beyond the PAR-range have little capacity to drive photosynthesis, however do affect plant development via a signaling response, i.e. the sense of photoperiodism, photo morphogenesis and phototropism. At wavelengths greater than ~750 nm there is no evidence of any substantial plant photosynthesis of signaling responses.

Of the many different light sources commercially available, most light sources emit light with a spectral composition that is very different from that of any natural daylight spectrum, as illustrated in Figure 1. Therefore, both perception of colour by the human eye and responses of living organisms to such lamp-light is also different from the response to natural daylight. For research purposes there are some light sources available that emit a spectrum that is more similar to that of natural daylight. No LED-based light fixture is available that combines the claims as described heretofore. Below the advantages of the characteristics of this invention are described for several fields of application.

For research the high similarity in spectral composition between the lighting fixture described here and natural daylight spectra is particularly useful. Especially the combination of the spectral properties and the option for constant current driving and dimming makes the lighting fixture described here an important new tool for both scientific and applied research. Important fields of scientific research benefitting from this invention are (photo)biology, medical sciences, material sciences (e.g. lifetime tests, photovoltaic panels etc.).

In photobiology, scientists investigate the responses of living organisms to a wide variety of influences. Often research is done in daylight-deficient environments. Because the lighting conditions in such a research environment are unnatural, the responses of the organism will be unnatural. As an example, plant breeders investigate crops with varying genotypes in an environment without natural daylight, whereas they are eventually interested in the responses of these genotypes in the field (under natural daylight). The spectral composition of light has a large effect on the responses of plants (see (Hogewoning et al. 2010, http://ixb.oxfordiournals.Org/content/61/5/1267.full) and also on some other living organisms (e.g. birds mammals, humans). Beside the spectral composition of the light often being unnatural in daylight-deficient environments, some light sources emit rhythmically pulsing flickering light, such as fluorescent tubes and most LED-based light sources. The discontinuous photon flux produced by such light sources may result in responses of living organisms that are different from response to a continuous flux of photons likewise in natural daylight or optionally possible using the invention described here. Pulsing light has been reported to have detrimental effects in humans and other species (Inger et a 1,2014, http://iournals.plos.org/plosone/article?id=10.1371/ioumal.pone.0Q98631). See for the effect of pulsing light on plants e.g. http://www.ncbi.nlm.nih.gov/pubmed/24307096 and the spectral composition of some common light sources figure 1.

Claims

1. The unique properties of this light source include the high degree of natural light / daylight equality in light spectrum, constant current control, spectrum preservation, and the ability to adjust the spectrum for targeted crop impact.

2. A light fixture consisting of: An array of Light Emitting Diodes (LEDs) which produces a light spectrum that is highly similar to the light spectrum of natural sunlight / daylight. The array can be composed of LED chips that emit wavelengths in a narrow bandwidth with a typical 20nm - 50 nm "Full Width or Half Maximum (FWHM)", or in a wide bandwidth with a typical 50 nm-450 nm FWHM, or a combination of narrowband and broadband radiating chips. Within the wavelength range 400 to 700 nm, the spectral composition of the light fixture can be adjusted to be comparable to natural daylight spectra as measured at the earth's surface. Typically a sunlight / daylight spectrum as available in the ASTM database (http://rredc.nrel.gOv/solar/spectra/aml.5/astmgl73/astmgl73.html) or a spectrum as measured during the day in the Netherlands (Hogewoning et al. 2010, Figure IA; http://ixb.oxfordiournals.Org/content/61/5/1267.full) are emitted by the lighting fixture. The lighting fixture can be adjusted within the wavelength range 400-700 nm so that it is at least 90% equal to the above-mentioned spectra within each 50-nm interval.

The light fitting of claim 1 can be dimmed with constant current control, whereby a continuous photon flux is also emitted during dimming while maintaining the spectral properties. Constant current control is unique for a LED-based light source with a spectral composition as described in claim 1. Optionally, dimming can also take place according to the PWM channel control and dimming principle, resulting in a pulsating flux photons while maintaining the spectral properties, which is the standard technique. for dimming LED-based light fixtures.

The light fitting of claim 1, can be adjusted so that the UV portion (wavelength range 350-400 nm) and a portion of the spectral range in the blue (400-430 nm) can be individually dimmed, with the possible purpose of influencing crop horticultural purposes and research in general (plant research, material testing, etc.).

The light fixture of claim 1, can be adjusted so that the red-colored spectral region (700-760 nm) can be dimmed individually, with the possible aim of influencing crops for horticultural purposes and research (plant research).

The light fitting of claim 1, produces a photon flux with an electrical efficiency of at least 0.8 μιτιοΙ photon flux per joule of electrical energy input.

The light fixture of claim 1, can be configured in a version> 200W power (thus> 160 μιτιοΙ photon-flux), so that it is suitable for illuminating substantial surfaces (typically 0.25 to 2 m2 for crop production or large surfaces for general lighting applications)

8. The LED light source is a multi-channel LED array composed of monochromatic and phosphor-coated LEDs in such a ratio that the radiated spectrum virtually mimics the spectrum of sunlight / daylight in the range of 400 to 700 nm or optionally from 360 to 760 nm.

9. The LED array is made up of monochromatic and phosphorus-coated (blend) LEDs. The LED array can be composed of the following narrow band LEDs: 360nm, 380nm, 405nm, 420nm, 450 nm, 470nm, 480nm, 485nm, 490nm, 495nm, 500nm, 630nm, 640 nm, 660 nm, 675nm, 705nm, 720nm, 730 nm, 745 nm and 765 nm. The LED array can also be composed of one or more types of phosphor-coated LEDs for 3000K, 515nm, 530nm, 560nm, 580nm and 630nm. For the assembly ('die bonding') of the LED chips, we mainly use "Chip on board (COB) technology". For the "die-bonding" process we use standard SMT processes for placement and soldering of the LED chips. This technique provides better heat conduction from the LED chip to the substrate, which improves the efficiency of the LED source by a factor of 9 compared to pakaged LEDs.

10. The spectrum contains 10 to 20 groups of LEDs with different spectral output. These groups are distributed over 20 channels, corresponding to a certain bandwidth of the spectrum and they all have their own current (CC) driver (s) circuit. These CC circuit chips have a temperature compensation input, which is used for tuning the response to ensure that the spectrum virtually mimics the sunlight / daylight. Outside of the initial factory settings, this input can later be used for calibration of the spectrum.

11. The full spectrum is subdivided into 3 main groups of bandwidths namely UV (350nm to 399nm), PAR (400nm to 700nm) and far red (701nm to 770nm). Each of these 3 groups can be individually dimmed from 28% to 100% light output. A minimum level of 28% is required to keep the LED driver chip in CC mode. During dimming, the spectrum virtually simulates sunlight / daylight when the main groups of bandwidths UV, PAR and far-red are exposed to a comparable dimming level / level.

12. During the start-up, a short time, a few minutes, is required to stabilize the spectrum. After this stabilization, the spectrum will remain stable regardless of the ambient temperature of 10 to 35 degrees Celsius. The stability of the spectrum is achieved by temperature compensation input from the CC LED driver Chip. The input of the constant current driver which is linear with the temperature change so that the integrating network sends out compensation related to the temperature change.

13. If the ambient temperature or the temperature of the LED array becomes too high, an overheating protection circuit will be activated which adjusts the three main groups of dim circuits so that the power is reduced. Also during this reduction in power the light spectrum will remain stable and only the light intensity will be lower. When the ambient temperature and / or the temperature of the LED array comes within specifications again, the power will be increased / restored to its most recent previous setting.

14. Figure 2, diagram of the lamp (black) shows the result of the spectrum compared to natural daylight in full sun (light gray) and heavy clouds (light gray). The result is an almost 100% fit with two natural sunlight conditions.