Cool White Fluorescent Research Articles

The influence of LEDs with different blue peak emission wavelengths on the biomass, morphology, and nutrient content of kale cultivars

Light-emitting diodes (LEDs) enhance plant production in vertical farms by regulating photosynthetic rate and phytochemistry. Specific light recipes can be formulated using LEDs for high output by fine-tuning spectral composition and irradiance. In this study, the growth, development, and nutritional quality of three kale cultivars (‘Toscano’, ‘Redbor’, and ‘Winterbor’) were examined under different blue peak emission wavelengths (λpeak). Photosynthetic photon flux density (PPFD) was maintained at 200 ± 10% μmol m − 2s − 1 over a 16-hr photoperiod. The LED light treatments had blue λpeak centered at 400, 420, and 450 nm wavelengths, all with spectral ratios of 20% blue, 20% green, 60% red in the visible light region, and 15% of total PPFD in the far-red region. The control light was cool-white fluorescent (CWF) light with blue λpeak at 436 nm and a slightly higher amount of PPFD in the blue region (23%). The biomass yield and leaf physical characteristics were largely unaffected by the light treatments with different blue λpeak. However, the concentration of carotenoids and chlorophylls in kale leaves was influenced by the type and amount of blue light during growth. Future research should investigate the effect of different blue light percentages in pre- and post-harvest LED treatments (continuous or pulsed) on high-value, nutritious crops.

Effect of light source and UVA quotient on monoclonal antibody stability during ambient light exposure studies

Therapeutic proteins such as monoclonal antibodies (mAbs) are exposed to ambient light conditions during manufacturing and handling processes, and the exposure time limits are generally determined by conducting relevant room temperature and room light (RT/RL) stability studies. In the case study presented here, a mAb drug product showed an unexpectedly higher level of protein aggregation during a formal RT/RL study conducted at a contract facility as compared to what had previously been seen during development studies. An investigation led to the finding that the RT/RL stability chamber was set up differently as compared to the one used for the internal studies. The UVA component of the light conditions used in the study was not representative of the conditions experienced by the drug product during normal manufacturing. During the investigation, three different light sources were evaluated for their UVA quotients along with the UV filtering effect of a plastic encasement. The mAb formulation showed a greater increase in aggregation when exposed to halophosphate and triphosphor-based cool white fluorescent (CWF) lights compared to a light emitting diode (LED) light. The plastic encasement on CWF lights significantly reduced the aggregation levels. Upon further assessment of additional mAb formulations, a similar trend was observed with sensitivity to the low level of UVA background emitted by the CWF lights. This study demonstrated that it is critical to understand UV levels at the sample handling level while setting up ambient light studies using CWF lights for biologic drug products. The use of non-representative light conditions (UV irradiance) can lead to unnecessary restrictions on the RL exposure allowance set for these products.

Influence of Light Phase Exposure to LED Lighting on Circadian Levels of Neuroendocrine Hormones in Sprague-Dawley Rats.

Light and lighting protocols of animal research facilities are critically important to the outcomes of biomedical research that uses animals. Previous studies from our laboratory showed that the wavelength (color) of light in animal housing areas affects the nocturnal melatonin signal that temporally coordinates circadian rhythms in rodents. Here, we tested the hypothesis that exposure to LED light enriched in the blue-appearing portion (460-480 nm) of the visible spectrum during the light phase (bLAD) influences circadian concentrations of select neuroendocrine hormones in adolescent Sprague-Dawley rats. Male and female rats (4 to 5 wk old) were housed on a novel IVC system under a 12L:12D in either cool-white fluorescent (control, n = 72) or bLAD (experimental, n = 72) lighting. Every third day, body weight and food and water consumption were measured. On Day 30, rats were anesthetized with ketamine/xylazine and terminal collection of arterial blood was performed to quantify serum concentrations of melatonin, corticosterone, insulin, and glucose at 6 circadian time points (0400, 0800, 1200, 1600, 2000, 2400). As compared with male and female rats housed under cool white fluorescent (CWF) lighting, rats in bLAD lighting showed a 6-fold higher peak in dark phase serum melatonin (P < 0.05). Effects on serum corticosterone were sex dependent, as CWF and bLAD females had significantly higher corticosterone levels than did CWF and bLAD males, respectively. CWF and bLAD females had significantly higher serum glucose overall as compared with males. However, serum insulin was not affected by sex (M or F) or lighting conditions (CWF or bLAD). These data show that housing Sprague-Dawley rats under bLAD lighting conditions increases circadian peaks of melatonin without increasing serum levels of corticosterone, glucose or insulin, indicating less variation of circadian cycling of key neuroendocrine hormones in bLAD-exposed rats.

Effects of Daytime Blue-Enriched LED Light on Physiologic Parameters of Three Common Mouse Strains Maintained on an IVC System.

Light has been a crucial part of everyday life since the beginning of time. Most recently, light-emitting diode (LED) light enriched in the blue-appearing portion of the visible spectrum (465 to 485 nm), which is more efficient in energy use, is becoming the normal lighting technology in facilities around the world. Previous reports revealed that blue-enriched LED light at day (bLAD) enhances animal health and wellbeing as compared with cool white fluorescent (CWF) lighting. We hypothesized that bLAD, compared with CWF light, has a positive influence on basic physiologic indices such as food consumption, water consumption, weight gain, nesting behavior, complete blood count, and blood chemistry profile. To test this, we allocated 360 mice into equal-sized groups by sex, strain (C3H/HeNCrl, C57BL/6NCrl, BALB/cAnNCrl), lighting conditions, and 6 blood collection time points (n = 5 mice/sex/strain/lighting condition/time point). Food consumption, water consumption, body weight, nest location, and nest type were recorded every 3 d. At the end of the study, all mice were anesthetized over a period of 1 wk and blood was collected via cardiocentesis at 6 different time points. Overall, male C3H/HeNCrl consumed more food under bLAD conditions as compared with CWF conditions; male C3H/HeNCrl had lower cholesterol levels under bLAD conditions than under CWF conditions; female BALB/cAnNCrl mice had higher serum total protein under bLAD conditions than under CWF conditions; female C57BL/6NCrl mice had higher phosphorus levels under bLAD conditions than under CWF conditions, and female C3H/HeNCrl mice had a higher neutrophil count under bLAD conditions as compared with CWF conditions. Although sex and strain differences were found in various physiologic parameters under bLAD as compared with CWF lighting conditions, the differences were minimal. Thus, this study suggests that for these strains of mice, bLAD and CWF are largely equivalent with regard to indices of health and wellbeing, although some differences could affect research outcomes.

Intra- and Inter-Model Variability of Light Detection Using a Commercially Available Light Sensor.

The veracity of claims made by researchers and clinicians when reporting the impact of lighting on vision and other biological mechanisms is, in part, reliant on accurate and valid measurement devices. We aim to quantify the intra- and inter-watch variability of a commercially available light sensor device which has been widely used in vision and other photobiological research. Intra- and inter-watch differences were investigated between four Actiwatch Spectrum Pro devices. The devices were used to obtain measurements on two separate occasions, under three different controlled light conditions; the Gretag Macbeth Judge II lightbox was used to produce Simulated Daylight (D65), Illuminant A (A) and Cool White Fluorescent (CWF) lighting. Significant inter-watch differences were noted when considering tricolour (red, green, blue) and the white sensor outputs under each of the three illuminants (p < 0.01). A significant interaction was also found between tricolour sensor and watch used (p < 0.01). Intra-watch differences were noted for the tricolour and for the white sensor outputs under the three illuminants (≤0.05), for all but one watch which showed no significant intra-watch difference for the white 'sensor output' under the D65 illuminant. Use of spectral sensitivity devices is an evolving field. Before drawing causal relationships between light and other biological processes, researchers should acknowledge the limitations of the instruments used, their validation, and the resultant data. The outcomes of the study indicate caution must be exercised in longitudinal data collection and the mixing of watches amongst study participants should be avoided.

Influence of Daytime LED Light Exposure on Circadian Regulatory Dynamics of Metabolism and Physiology in Mice.

Light is a potent biologic force that profoundly influences circadian, neuroendocrine, and neurobehavioral regulation in animals. Previously we examined the effects of light-phase exposure of rats to white light-emitting diodes (LED), which emit more light in the blue-appearing portion of the visible spectrum (465 to 485 nm) than do broad-spectrum cool white fluorescent (CWF) light, on the nighttime melatonin amplitude and circadian regulation of metabolism and physiology. In the current studies, we tested the hypothesis that exposure to blue-enriched LED light at day (bLAD), compared with CWF, promotes the circadian regulation of neuroendocrine, metabolic, and physiologic parameters that are associated with optimizing homeostatic regulation of health and wellbeing in 3 mouse strains commonly used in biomedical research (C3H [melatonin-producing], C57BL/6, and BALB/c [melatonin-non-producing]). Compared with male and female mice housed for 12 wk under 12:12-h light:dark (LD) cycles in CWF light, C3H mice in bLAD evinced 6-fold higher peak plasma melatonin levels at the middark phase; in addition, high melatonin levels were prolonged 2 to 3 h into the light phase. C57BL/6 and BALB/c strains did not produce nighttime pineal melatonin. Body growth rates; dietary and water intakes; circadian rhythms of arterial blood corticosterone, insulin, leptin, glucose, and lactic acid; pO₂ and pCO₂; fatty acids; and metabolic indicators (cAMP, DNA, tissue DNA 3H-thymidine incorporation, fat content) in major organ systems were significantly lower and activation of major metabolic signaling pathways (mTOR, GSK3β, and SIRT1) in skeletal muscle and liver were higher only in C3H mice in bLAD compared with CWF. These data show that exposure of C3H mice to bLAD compared with CWF has a marked positive effect on the circadian regulation of neuroendocrine, metabolic, and physiologic parameters associated with the promotion of animal health and wellbeing that may influence scientific outcomes. The absence of enhancement in amelatonic strains suggests hyperproduction of nighttime melatonin may be a key component of the physiology.

Effect of Daytime Blue-enriched LED Light on the Nighttime Circadian Melatonin Inhibition of Hepatoma 7288CTC Warburg Effect and Progression.

Liver cancer is the second leading cause of cancer death worldwide. Metabolic pathways within the liver and liver cancers are highly regulated by the central circadian clock in the suprachiasmatic nuclei (SCN). Daily light and dark cycles regulate the SCN-driven pineal production of the circadian anticancer hormone melatonin and temporally coordinate circadian rhythms of metabolism and physiology in mammals. In previous studies, we demonstrated that melatonin suppresses linoleic acid metabolism and the Warburg effect (aerobic glycolysis)in human breast cancer xenografts and that blue-enriched light (465-485 nm) from light-emitting diode lighting at daytime (bLAD) amplifies nighttime circadian melatonin levels in rats by 7-fold over cool white fluorescent (CWF) lighting. Here we tested the hypothesis that daytime exposure of tissue-isolated Morris hepatoma 7288CTC-bearing male rats to bLAD amplifies the nighttime melatonin signal to enhance the inhibition of tumor growth. Compared with rats housed under a 12:12-h light:dark cycle in CWF light, rats in bLAD light evinced a 7-fold higher peak plasma melatonin level at the mid-dark phase; in addition, high melatonin levels were prolonged until 4 h into the light phase. After implantation of tissue-isolated hepatoma 7288CTC xenografts, tumor growth rates were markedly delayed, and tumor cAMP levels, LA metabolism, the Warburg effect, and growth signaling activities were decreased in rats in bLAD compared with CWF daytime lighting. These data show that the increased nighttime circadian melatonin levels due to bLAD exposure decreases hepatoma metabolic, signaling, and proliferative activities beyond what occurs after normal melatonin signaling under CWF light.

Abstract 3191: Daytime blue-enriched LED light-induced circadian amplification of the nighttime melatonin signal increases sorafenib sensitivity in human hepatocellular carcinoma via enhanced suppression of the Warburg effect

Abstract Over 36,000 people in the United States will be diagnosed with hepatocellular carcinoma (HCC) in 2016, the second leading cause of cancer death worldwide. Metabolic pathways within the liver and in HCC are highly regulated by the central circadian clock in the suprachiastmatic nucleus (SCN). The SCN drives nighttime production of the circadian anti-cancer hormone melatonin by the pineal gland in rats and humans. We have shown that the nighttime circadian melatonin signal suppresses the Warburg effect (aerobic glycolysis) in human breast cancer xenografts and that blue-enriched light (460-480 nm) from LEDs at daytime (bLAD), amplifies the nighttime circadian melatonin signal by 7-fold in rats over cool white fluorescent (CWF) lighting. Here we tested whether daytime exposure of tissue-isolated HepG2 xenograft-bearing male nude rats to bLAD amplifies the nighttime melatonin signal to increase tumor sensitivity to nighttime administered sorafenib (FDA-approved multi-kinase inhibitor) treatment via enhancing suppression of the Warburg effect. Animals were randomized to 6 subgroups (n = 4): CWF Groups I, 12 h light:12 h dark (LD,12:12) (CWF + vehicle) and II (CWF + sorafenib); bLAD Groups III (LD,12bLAD:12) (bLAD + vehicle), IV (bLAD + sorafenib), V (bLAD + S20928 MT1/MT2 receptor blocker), and VI (bLAD + S20928 + sorafenib). Drug treatments began when tumors were 2.5 g estimated weight. Plasma nighttime melatonin levels were 7-fold higher in Groups III-VI, compared to Groups I and II. Tumor latency-to-onset of growth and growth rates were markedly delayed and decreased, respectively, in Group III compared to Group I. Sorafenib induced tumor regression at a rate that was 2-fold higher in the bLAD- vs CWF-exposed rats. Tumor glucose uptake and lactate production (Warburg effect) at the mid-dark phase were significantly reduced in CWF-exposed rats receiving sorafenib vs vehicle. In vehicle-treated bLAD-exposed rats, the Warburg effect was significantly decreased vs CWF-exposed rats receiving vehicle. In bLAD + sorafenib-treated rats, the Warburg effect was reduced by an additional 51% (glucose uptake) and 89% (lactate production), respectively, vs CWF + sorafenib-treated rats. Melatonin receptor blocker S20928 completely prevented the effects of bLAD and bLAD + sorafenib on the Warburg effect and made these tumors completely resistant to sorafenib-induced tumor regression. These findings are the first to show in vivo that: 1) nighttime circadian sorafenib therapy inhibited the Warburg effect and induced HepG2 tumor regression under CWF lighting conditions, and 2) the bLAD-amplified nocturnal circadian melatonin signal increased tumor sensitivity to sorafenib-induced regression by enhancing a melatonin receptor-mediated suppression of the Warburg effect. Citation Format: Robert T. Dauchy, David T. Pointer, Aaron E. Hoffman, Melissa A. Wren-Dail, Shulin Xiang, Lin Yuan, David E. Blask, Victoria P. Belancio, Steven M. Hill. Daytime blue-enriched LED light-induced circadian amplification of the nighttime melatonin signal increases sorafenib sensitivity in human hepatocellular carcinoma via enhanced suppression of the Warburg effect [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3191. doi:10.1158/1538-7445.AM2017-3191

The Photosensitizing Potential of Compact Fluorescent vs Incandescent Light Bulbs

Recently an article about the new energy-saving compact fluorescent light (CFL) bulbs appeared in Parade magazine [Rosenfeld, I. (2008) Parade Feb 3, 22]. Under the heading "Bright Lights, Bad Headache?" the writer states that "new research suggests some dangers" involving these lights because they are fluorescent and "can aggravate skin rashes in people with lups, eczema, dermatitis or porphyria." We measured the emission spectrum of a 14 W compact fluorescent bulb (with the same luminous flux as a 60 W incandescent bulb) and compared it to 60 W soft white incandescent and cool white fluorescent (CWF) bulbs. Our results clearly show that the spectral irradiance of the compact fluorescent bulb is similar to that of the CWF bulb; both exhibit sharp Hg emission lines at 365 nm (very weak), 404 nm (weak), 435 nm (moderate) and 543 nm (strong). In contrast, the emission of the incandescent bulb begins at 375 nm and then increases monotonically to above 750 nm. From their respective absorption spectra we calculated the potential photosensitization indices of protoporphyrin IX (PPIX; a prototypic porphyria skin photosensitizer) and riboflavin (a putative lens photosensitizer) vs 14 W compact fluorescent, CWF and 60 W incandescent bulbs. A higher photosensitization index would indicate a greater chance that the light/photosensitizer combination would cause photosensitization of the skin or eyes. We found that for PPIX and riboflavin the photosensitization index of the compact fluorescent bulb is less than half that of the 60 W incandescent bulb. These results suggest that substitution of a compact fluorescent bulb for an incandescent bulb of the same luminous flux should not increase the phototoxicity of skin porphyrins or lens riboflavin.

(296) Effects of Lighting Intensity on the Yield of Tomato and Pepper Crops Grown under Space Station (ISS) Environmental Conditions

Of the many environmental variables, light intensity (PPF) has primary effect on photosynthesis and significantly influences crop yield. With the eventual use of a crop production system on the International Space Station (ISS), Mars transit vehicle, or in a lunar/Martian habitat, there exists certain engineering constraints that will likely affect the lighting intensity available to plants. Tomato and pepper are candidate crops being considered by NASA that were selected based on their applicability to such mission scenarios. To study the effects of lighting intensity, tomato (Lycopersicon esculentum L. cv. Red Robin) and pepper (Capsicum annuum L. cv. Hanging Basket) plants were grown under cool-white fluorescent (CWF) lamps with light intensities of 8.6, 17.2, or 26 mol·m-2 ·d-1, with a constant air temperature of 25 °C, 65% relative humidity, and CO2 supplementation of 1200 μmol·mol-1 in order to duplicate conditions plants might be subjected to in an open environment of a space cabin. Following 105 days of growth, edible and total mass for both tomato and pepper increased with increasing light levels. Fruit development and time to ripening was also affected by light treatments. The effects of lighting when combined with other environmental factors typical of spaceflight systems will help define crop production for future missions that incorporate plant-based life support technologies.

(298) Lighting Intensity and Temperature: How They Affect the Yield of Salad Crops Grown under ISS Baseline Environmental Conditions

Environmental factors such as light intensity (PPF) and/or air temperature may be limiting engineering constraints in near or long-term space missions. This will potentially affect NASA's ability to provide either dietary augmentation to the crew or maintain a large-scale bioregenerative life support system. Crops being considered by NASA to provide supplemental food for crew consumption during such missions consist primarily of minimally processed “salad” species. Lettuce (Lactuca sativa L. cv. Flandria), radish (Raphanus sativus L. cv. Cherry Bomb II), and green onion (Allium fistulosum L. cv. Kinka) are being evaluated under a range of PPF and temperature environments likely to be encountered in space systems. Plants were grown for 35 days under cool-white fluorescent (CWF) lamps with light intensities of 8.6, 17.2, or 26 μmol·m-2·d-1, at air temperatures of 25 and 28 °C, and 50% relative humidity, and 1200 μmol·mol-1 CO2. Regardless of temperature, all three species showed an increase in edible mass with increasing light levels. When grown at 28 °C, edible mass of radish was significantly reduced at all lighting intensities compared to 25 °C, indicating a lower optimal temperature for radish. Understanding the interactions of these environmental factors on crop performance is a critical element to defining future missions that incorporate plant-based life support technologies.

Performance of Three Species of Salad-type Plants Grown under Narrow-spectrum Light-emitting Diodes (LEDs) in a Controlled Environment

Light-emitting diodes (LEDs) are a promising light source for growing crop plants in spaceflight systems because of their superior safety, durability, small mass and volume, wavelength specificity, and long life. To address the usefulness of LEDs as a plant lighting source, radish (Raphanus sativus L. cv. Cherriette), lettuce (Lactuca sativa L. cv. Waldmann's Green), and spinach (Spinacea oleracea L. cv. Nordic IV) were grown using nutrient film technique hydroponics under cool-white fluorescent (CWF) lamps, red LEDs (peak emission 660 nm), and red LEDs + 30 μmol·m–2·s–1 supplemental blue fluorescent (BF) light (400–500 nm). Each lighting treatment was maintained in a separate controlled-environment chamber with total photosynthetic photon flux (PPF) maintained near 300 μmol·m–2·s–1 and a photoperiod of 18-h light/06-h dark. Results showed significant reductions in total dry mass (TDM) accumulation for radish plants grown under red LEDs + 30 μmol·m–2·s–1 BF or red LEDs only as compared to CWF-grown plants. Although TDM tended to decrease with decreasing BF for lettuce, treatment differences were not significant. TDM for spinach plants was significantly less under red LEDs compared to CWF or red LEDs + 30 μmol·m–2·s–1 BF. Interestingly, single-leaf photosynthesis and leaf conductance were not significantly different for any treatment, regardless of species. The data suggest a species-specific response for the amount of blue necessary for normal plant growth.

Diurnal Temperature Alterations Influence Final Height of Herbaceous Perennials

DIF is the difference between day (DT) and night (NT) temperatures. Temperature drop is a 2-hour temperature reduction at sunrise. DIF and temperature drop, which can be affected by light quality, are effective methods to control final plant height of many greenhouse crops. The effect of DIF and temperature drop on final height was determined for eight species of perennials. Durations for DIF temperatures were 12 hours for both DT and NT. Temperature alterations occurred at sunrise. Temperature treatments (DT/NT) consisted of zero DIF (20/20°C), negative DIF (16/24°C), or positive DIF (24/16°C), and a 2-hour drop (12.7/20.7°C). Long days (LD) were provided from 2200-0200 hr by either cool-white fluorescent (CWF) or incandescent (INC) lights. Data for days to visible bud and anthesis, bud number, and final height were collected. Positive DIF conditions enhanced elongation while negative DIF reduced it in all species. As DIF decreased from positive to negative, plant height was reduced 10%, 30%, 30%, and 20% in Coreopsis `Moonbeam' and `Sunray', Delphinium `Belladonna', and Scabiosa `Butterfly Blue', respectively. Negative-DIF responses were enhanced under CWF lights for some species. In negative-DIF conditions, Coreopsis `Moonbeam' and `Sunray' and Delphinium `Belladonna' were 10%, 10%, and 15% shorter, respectively, under CWF lights than INC lights.

Effects of Temperature, Photoperiod, and Light Quality on Flowering in Several Herbaceous Perennial Species

The influence of low temperatures on Campanula carpatica `Blue Clips' and Lavandula angustifolia `Munstead' flowering was determined; plants were stored at 5C for several weeks and forced under 9-h photoperiods with a 4-h night interruption (NI). C. carpatica, L. angustifolia, and Asclepias tuberosa were forced under NI at five temperatures (15–27C) and time to flower under each treatment was calculated. Flower number and size were reduced at highest temperatures. The effectiveness of cool-white fluorescent (CWF), high-pressure sodium (HPS), incandescent (I), and metal halide (MH) lights in inducing flowering in C. carpatica and Coreopsis lanceolata `Early Sunrise' was compared. Lighting was delivered as a 7-h daylength extension with PPF ranging from 0.05–2.0 μmol·m–2·s–1. Minimum irradiances above which all C. carpatica flowered were approximately 0.14, 0.12, 0.1, and 0.17 μmol·m–2·s–1, respectively. C. lanceolata under CWF displayed irregular flowering throughout the range of intensities used. Under HPS and MH, minimum irradiances for 100% flowering were 0.37 and 1.0 μmol·m–2·s–1, respectively, with sporadic flowering at lower intensities. Under I light, all C. lanceolata exposed to 0.12 μmol·m–2·s–1 or more flowered.

Photochemical Reduction of Ferric Iron by Chelators Results in DNA Strand Breaks

The induction of single-strand breaks (SSB) in φX174 RFI DNA by Fe(III) chelates under cool-white fluorescent (CWF) light or in darkness was investigated. Under CWF light, ferric iron (25 μM) without the addition of a low-molecular-weight (LMW) chelator or with the addition of a LMW chelator, such as citrate, nitrilotriacetate (NTA), or EDTA, generated SSB in 11, 30, 13, or 0% of the treated, closed-circular DNA, respectively. Addition of 11202 increased the formation of DNA SSB to 93, 75, 62, or 25, respectively. In the dark, DNA SSB were not detected in the absence of H2O2. The addition of H2O2 resulted in 85% (none), 8% (citrate), 18% (EDTA), or 42% (NTA) DNA with SSB. The formation of DNA SSB was completely inhibited by a strong Fe(II)-specific chelator, ferrozine. Various .OH scavengers (e.g., mannitol, 5,5-dimethyl-1-pyrroline-N-oxide, dimethyl sulfoxide) completely inhibited DNA SSB formation in the presence of a LMW chelator, but only partially inhibited in the absence. These results suggest that Fe(II) and .OH or similarly reactive species may be involved in the induction of DNA SSB. The evolution of CO2 from chelators, such as EDTA or citrate, required CWF light and Fe(III), suggesting the participation of chelators in the reaction with Fe(III). Under CWF light, catalase inhibited and so-peroxide dismutase (SOD) stimulated formation of DNA SSB, indicating H2O2 was generated from O2 and was required for DNA damage. In the dark, SOD inhibited formation of DNA SSB, suggesting O2 was required for reaction(s) other than formation of H2O2. These results suggest that in the light the photochemical reduction of Fe(III) by the chelators results in formation of DNA SSB without the addition of H2O2. In the dark, the addition of H2O2 was required for the formation of DNA SSB, suggesting a different mechanism for DNA strand break formation.

Comparison of Fluorescent and High-pressure Sodium Lamps on Growth of Leaf Lettuce

Radiation from high-pressure sodium (HPS) lamps provided more than a 50% increased yield (fresh and dry weight of tops) of loose-leaf lettuce cultivars Grand Rapids Forcing and RubyConn, compared to that obtained by radiation from cool-white fluorescent (CWF) lamps at equal photosynthetic photon flux; yet, input wattage was approximately 36% less. It was postulated that the considerable output of 700 to 850 nm radiation from the HPS lamp was a significant factor of the increased yield. Under HPS lamps, the leaves of both cultivars were slightly less green with very little red pigmentation ('RubyConn') and slightly elongated, compared to CWF, but plant productivity per unit electrical energy input was vastly superior with HPS.

Influences of ultra‐violet (UV)‐blue light radiation on the growth of cotton. I. Effect on iron nutrition and iron stress response

Abstract Cool white fluorescent (CWF) light reduces Fe3+ to Fe2+ while low pressure sodium (LPS) light does not. Cotton plants grown under CWF light are green, while those yrown under LPS light develop a chlorosis very similar to the chlorosis that develops when the plants are deficient in iron (Fe). It could be that CWF light (which has ultra violet) makes iron more available for plant use by maintaining more Fe2+ in the plant. Two of the factors commonly induced by Fe‐stress in dicotyledonous plants‐‐hydroyen ions and reductants released by the roots‐‐were measured as indicators of the Fe‐deficiency stress response mechanism in M8 cotton. The plants were grown under LPS and CWF light in nutrient solutions containing either NO3‐N or NH4‐N as the source of nitrogen, and also in a fertilized alkaline soil. Leaf chlorophyll concentration varied significantly in plants grown under the two light sources as follows: CWF+Fe > LPS+Fe > CWF‐Fe ≥ LPS‐Fe. The leaf nitrate and root Fe concentrations were significant...

Growth and tuberization of potato (Solanum tuberosum L.) under continuous light.

The growth and tuberization of potatoes (Solanum tuberosum L.) maintained for 6 weeks under four different regimes of continuous irradiance were compared to plants given 12 hours light and 12 hours dark. Treatments included: (a) continuous photosynthetic photon flux of 200 micromoles per square meter per second cool-white fluorescent (CWF); (b) continuous 400 micromoles per square meter per second CWF; (c) 12 hours 400 micromoles per square meter per second CWF plus 12 hours dim CWF at 5 micromoles per square meter per second; (d) 12 hours [400] micromoles per square meter per second CWF plus 12 hours dim incandescent (INC) at 5 micromoles per square meter per second and a control treatment of 12 hours light at 400 micromoles per square meter per second CWF and 12 hours dark. The study included five cultivars ranging from early- to late-season types: 'Norland,' 'Superior,''Norchip,' 'Russet Burbank,' and 'Kennebec,' Tuber development progressed well under continuous irradiation at 400 micromoles per square meter per second and under 12 hours irradiance and 12 hours dark, while tuber development was suppressed in all other light treatments. Continuous irradiation at 200 or 400 micromoles per square meter per second resulted in severe stunting and leaf malformation on 'Superior' and 'Kennebec' plants, but little or no injury and vigorous shoot growth in the other cultivars. No injury or stunting were apparent under 12-dim light or 12-dark treatments. Plants given 12 hours dim INC showed significantly greater stem elongation but less total biomass than plants in other treatments. The continuous light encouraged shoot growth over tuber growth but this trend was overridden by providing a high irradiance level. The variation among cultivars for tolerance to continuous lighting indicates that potato may be a useful species for photoinhibition studies.

Influence of Lighting Systematics on the Interior Performance of Two Croton Cultivars

Abstract Codiaeum variegatum (L.) Blume var. pictum (Lodd.) Mull, Agr. ‘Bravo’ and ‘Normal’ were produced for 8 months under light levels of 950, 650, or 350 μmol s-1m-2 before being held for 4 months indoors under 6, 12, or 24 hr light duration using either cool-white fluorescent (CWF) or incandescent (INC) lamps. After 8 months of growth in production, plant width and leaf length increased whereas leaf number, thickness, and variegation decreased as production light level decreased. The best quality plants with moderate variegation and adequate growth were those produced under 650 μmol s-1m-2. After 4 months indoors, ‘Bravo’ tolerated interior light conditions more successfully than ‘Norma’. Plants previously produced under 350 μmol s-lm-2 retained more leaves and maintained better plant quality than other production light treatments. Leaf retention was best with 12 hr of postproduction light duration. Adequate lighting to maintain the quality of properly acclimatized plants was provided by either CWF or INC lamps.

Keeping Quality of Ficus benjamina as Affected by Production Light Levels and Postproduction Light Quality and Level

Abstract F. benjamina L. were produced in a greenhouse shaded to provide a maximum natural light level of 400 or 800 μmol s-1m-2 photosynthetic photon flux density (PPFD) for 5 months. Plants were held indoors for 12 weeks under incandescent (INC) or cool-white fluorescent (CWF) lamps at 10 μmol s-1m-2 or 20 μmol s-1m-2 for 12 hr/day. Leaf drop was substantially reduced and plant quality was increased when plants were produced under 800 μmol s-1m-2 or when plants were held indoors under 20 μmol s-1m-2 of light. Leaf loss in response to production light levels, postproduction light levels, and light source was different when measured over time. Dry weight was increased when plants were produced under 800 μmol s-1m-2. Chlorophyll content was increased in plants grown under 400 μmol s-1m-2 or held under CWF lamps.