Browsing by Subject "light"

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  • Hari, Pertti; Salminen, Raimo; Pelkonen, Paavo; Huhtamaa, Mikko; Pohjonen, Veli (Suomen metsätieteellinen seura, 1976)
  • Väisänen, Eero; Kellomäki, Seppo; Hari, Pertti (Suomen metsätieteellinen seura, 1977)
  • Kellomäki, Seppo; Oker-Blom, Pauline (Suomen metsätieteellinen seura, 1983)
  • Greis, Ilppo; Kellomäki, Seppo (Suomen metsätieteellinen seura, 1981)
  • Kellomäki, Seppo; Hari, Pertti (Suomen metsätieteellinen seura, 1980)
  • Kellomäki, Seppo; Hari, Pertti; Kanninen, Markku; Ilonen, Pirkko (Suomen metsätieteellinen seura, 1980)
  • Kellomäki, Seppo; Kanninen, Markku (Suomen metsätieteellinen seura, 1980)
  • Pukkala, Timo; Kuuluvainen, Timo (Suomen metsätieteellinen seura, 1987)
  • Nygren, Markku (Suomen metsätieteellinen seura, 1987)
    Tests on seeds from a natural stand and from a clone archive, with various photoperiods and temperature regimes, showed that germination was delayed at low temperature (10 degrees C) and in darkness. This effect diminished the later in autumn seeds were collected.
  • Alasaarela, Juha (Helsingin yliopisto, 2019)
    Ruukkusalaattien tuotanto on kasvanut Suomessa jo vuosikymmeniä. Kasvihuoneet mahdollistavat tuoreiden lehtivihannesten kasvatuksen ympärivuotisesti, mutta pimeä vuodenaika tai valonsaannin heikentyminen yhdessä korkean nitraattilannoituksen kanssa aiheuttavat nitraatin kertymistä salaattiin. Nitraatti ei itsessään ole kovin myrkyllistä ihmiselle, mutta sen aineenvaihduntatuotteet elimistössä voivat olla haitallisia. Siksi ravinnon nitraattipitoisuuksia rajoitetaan EU asetuksella ja kasvisten nitraattipitoisuuksia valvoo Ruokavirasto. Tutkimuksen tavoitteena oli selvittää jääsalaatin (Lactuca sativa L.) nitraattipitoisuuteen vaikuttavia tekijöitä yksityisellä kasvihuonepuutarhalla, ja ehdottaa helposti sovellettavia keinoja nitraattipitoisuuden alentamiseksi. Tutkimuksessa mitattiin vuorokaudenajan, iän ja olosuhteiden vaikutusta jääsalaatin nitraattipitoisuuteen. Mittaukset tehtiin eri kellonaikoina korjatuilta salaateilta, neljän, viiden ja kuuden viikon ikäisiltä salaateilta, sekä viikoittaisilla seurantamittauksilla kolmen kuukauden ajan syksyllä 2017. Salaattien nitraattipitoisuus määriteltiin pikamittausmenetelmällä. Kasveille tulevaa PAR-valoa ja kiertoliuoksen nitraattityppipitoisuutta mitattiin jatkuvatoimisella mittalaitteella. Lisäksi kasvihuoneen automaattisesta ohjausjärjestelmästä saatiin tietoa muista kasvuolosuhteista. Sadonkorjuun kellonaika ei vaikuttanut jääsalaatin nitraattipitoisuuteen. Ikä vaikutti neljän ja viiden viikon ikäisten salaattien nitraattipitoisuuteen, mutta paremmissa valo-olosuhteissa iän vaikutus heikkeni kuuden viikon ikäisillä salaateilla. Nitraattityppilannoituksella ei ollut suoraa vaikutusta salaatin nitraattipitoisuuteen, mutta enemmän valoa saaneissa salaateissa oli vähemmän nitraattia. Kasvuston tasolta tehdystä jatkuvatoimisesta valon mittauksesta on hyötyä salaatin nitraattipitoisuuden hallinnassa. Riski nitraatin enimmäispitoisuusrajan ylitykseen on suuri syyskuussa luonnonvalon määrän vähentyessä. Tekovalojen käytön lisäämisellä voidaan alentaa salaatin nitraattipitoisuutta.
  • Solala, Kari (Helsingfors universitet, 2009)
    The literature review of this thesis deals with light, different light sources and their properties. LED (Light Emitting Diode) light was specially taken into consideration, because the use of LED lights will increase in general illumination. The literature review also deals with the quality changes of dairy products and potatoes caused by exposure to light. The aim of this study was to search for such a spectral distribution of light which would cause only minor changes in the sensory quality of milk and the surface colour of potatoes. Objective was to also find out if there is a difference between the effects of fluorescent light and LED light on the quality of milk and greening of potatoes. Reduced (1,5 %) fat milk and new potatoes were used as testing materials. The milk in commercial carton board packages was exposed to six different light sources: white fluorescent lamp, white LED and LED of four different colours. The potatoes packed in transparent LDPE (Low Density Poly Ethylene) bags were stored under five different light sources: white fluorescent lamp, white LED and LED of three different colours. The light intensity at the surface of the packages was about 1000 lx in both studies. In the milk study, the effects of light were evaluated with a sensory method using descriptive analysis. In the potato study, the light effects were analysed with colour measurements (avalue) using a spectrophotometer and with surface temperature measurements using a laser thermometer. Sensory evaluation of milk there resulted in few statistically significant differences in the intensity of the attributes between the milks stored under different light sources. Light exposure caused a rapid greening of potatoes in every illumination. According to colour change percentage, the greening order under different lights was: white LED < yellow LED < green LED < turquoise LED < fluorescent light. The potatoes which were stored in dark had no change in their surface colour. The surface temperature of potatoes increased most under white LED and turquoise LED lights. A spectral distribution of light which would have caused less changes in sensory quality of milk than commonly used fluorescent light was not found in this study. The results showed, however, that in addition to blue light which has always been considered the most harmful for milk the red light also caused remarkable quality changes. Based on the results of this study, it could be suggested that under the LED lights the quality of packed milk retained its quality characteristics at least as well as under the fluorescent light. There were differences between the effects of different lights on the greening of potatoes. White and yellow LED light caused less greening of potatoes than the other lights. The strongest greening of potatoes was observed under the fluorescent light.
  • Smolander, Heikki (Suomen metsätieteellinen seura, 1984)
    Measurements were made of temporal and spatial microvariations in irradiance in a small part of the canopy of a 20-yr-old Scots pine stand. Linear integration of the variations gave biased estimates; second order Taylor series approximations were satisfactory only for a low curvature response; two-point distribution approximations were applicable to high and low curvature response but presupposed that the mean and variance were known. It is suggested that a light measuring method in which first power (mean) and second power (variance) of irradiance are integrated resolves these problems; the method takes into account the geometry of the shoot and can also be used in transpiration studies.
  • Kuusipalo, Jussi (Suomen metsätieteellinen seura, 1985)
  • Oker-Blom, Pauline (Suomen metsätieteellinen seura, 1986)
    In modeling canopy structure, a statistical approach is applied to assign the location and orientation of plant parts; the radiation field is described in terms of random variables and their distributions. A comparison of horizontally homogeneous stands and grouped forest stands showed that grouping reduced interception of radiation and increased spatial variation. In conifers, the grouping of needles into shoots and the effect of penumbra had an important influence on the distribution of radiation on the needle area.
  • Kellomäki, Seppo; Väisänen, Eero; Kauppi, Pekka; Hari, Pertti (Suomen metsätieteellinen seura, 1977)
  • Kellomäki, Seppo; Oker-Blom, Pauline (Suomen metsätieteellinen seura, 1981)
  • Kotiranta, Stiina (Helsingfors universitet, 2014)
    Plant growth and morphology can be manipulated with light. Previously light manipulation experiments were mostly conducted by modifying the solar spectrum with light absorbing filters. Today, research can be conducted with modern LED lighting techniques, which enables specific spectrum tailoring. Light can be tailored specifically for a species or a family, and the needs of the farmer can also be taken into consideration. In this study, tomato (Solanum lycopersicum L. cv ’Efialto’) seedlings were grown under six different spectra. Plant morphology, stomatal function and drought tolerance were measured. Growth measurements included stem height, plant fresh and dry weight, leaf -area and leaf number. In addition, the effect of light quality on leaf morphology was studied by measuring leaf blade and petiole length. All measurements were conducted on well-watered and water-stressed plants, in order to study the effect of drought on vegetative growth and drought tolerance. Stomata conductance was studied by measuring leaf temperature prior to and during water stress. Leaf surface temperature indicates transpiration rate; thus the higher the conductance the lower leaf temperature. In addition to leaf temperature measurements, photosynthesis and stomatal conductance were measured by leaf level infra-red gas analysis. R:FR ratio was the dominant factor for affecting plant morphology. However, the B:G ratio also played a key role; when the B:G ratio was low, it further enhanced the elongation growth, a response caused by low R:FR ratio. Irradiance in green and yellow wavebands regulated stomatal closure. During water stress, the light treatment with the highest green irradiance, induced more rapid stomatal closure which was evident as increased leaf temperature and decreased gas exchange. Light-depenedent stomatal closure and decreased transpiration could explain the improved performance of these seedlings during the drought period. Light spectral quality thus affected the drought tolerance of tomato plants through its effects on plant morphology and stomata function.
  • Hårdh, J. E. (Suomen metsätieteellinen seura, 1966)