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seed germination and light colors

Seed germination and light colors

Can you help me with my experiments into the effect of different colourerd lights on the germination and growth of cress seeds?

This is really a very open-ended investigation. In order to compare your results with anyone else’s, we would need to know a huge amount of information – like the details of the exact filters you are using to produce your coloured lights.

However, far more important is the fact that this is a genuine investigation on your part and the results you get will be the answer to the question with relation to YOUR seeds and YOUR filters in YOUR laboratory.

So long as you collect numerical data (lengths of roots, number of seeds germinated, lengths of shoots etc) you will have data which you can tabulate, plot on graphs, carry out statistical analysis and generally show that you know HOW to carry out a scientific investigation, which is what the exercise is all about at A level.

Two things are changing in your experiments. First, the QUANTITY of light getting to each treatment – each filter will let through a different amount of light. Secondly, the colour of the light – filters do not let through light of only ONE wavelength, but a spread of wavelengths centred around the colour they appear to be. Then you have to consider whether the seed/seedling is able to ABSORB the colour of light you are exposing it to eg. leaves are green because they do not absorb much green light.

Student Sheet 8 on our site may offer a suitable protocol for this investigation.

Can you help me with my experiments into the effect of different colourerd lights on the germination and growth of cress seeds?

How Can Red Light Improve Germination & Production in Tomatoes?

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Visible white light can be divided into several colors, or wavelengths. These colors have varying effects on plant growth. For example, plants reflect rather than use green light, but red and blue light are both used for photosynthesis. Annual tomatoes (Solanum lycopersicum) require high amounts of light, and when grown indoors, the use of red light increases plant growth and production.

Plant Light Wavelengths

The best wavelengths for growing plants, including tomatoes, are blue, red and far-red light. Blue light, with a 450-nm wavelength, is good for starting seeds. Once seeds have sprouted, both blue light and red light, with 650-nm wavelengths, are essential for photosynthesis. Without blue and red light, the plants are not able to produce food. In addition, red light and far-red light, with the longest of the three wavelengths at 730 nm, cause plants to flower and are thereby essential for fruit production.

Red Light and Germination

Although seeds can be started under blue light alone, they do not grow well without the addition of red light once seedlings appear. Blue and red lights together promote leafy, vegetative growth. New tomato seedlings should be given 12 to 14 hours of light per day, either from a combination of natural sunlight and grow lights or exclusively from artificial lights that supply both red and blue wavelengths.

Red Light and Flowers

Mature tomato plants require at least six to eight hours of direct light per day. Because plants must flower to produce a large crop of tomatoes, light in the red and far-red wavelengths is essential for growing tomatoes. These wavelengths encourage flowering, and more flowers equal more tomatoes. Indoors or in greenhouses, where pollinators such as bees and wind are not available, these flowers must be pollinated by hand. To do this, gently shake the plants once a day between 9 a.m. and 1 p.m.

Sources for Red Light

There are several sources for supplying red light to tomatoes. Incandescent light bulbs contain red and far-red light but produce too much heat to be used exclusively. Broad spectrum florescent bulbs have both red and blue wavelengths, and they can be paired with incandescent lights to supply both red and far-red light. Use a ratio of 3 watts of fluorescent light per watt of incandescent light. Alternately, a mixture of red and blue light-emitting diode grow lights can be used for tomato production. LEDs produce low levels of heat and can be placed close to the leaves.

  • University of Massachusetts, Amherst: Growing Plants Indoors Under Lights
  • The Ohio State University Extension: Vegetable – Tomato (Solanum Lycopersicum)
  • Purdue Agriculture: Agricultures Magazine: Greenhouse Tomatoes in Red and Blue
  • University of Kentucky Extension: Greenhouse Tomato Production Practices

After graduating from The Ohio State University, Marissa Baker turned her attention to professional writing. Her experience covers a variety of topics, including gardening, landscaping and lawn care equipment. She has been gardening for as long as she can remember, and writing about garden and lawn care since 2012.

How Can Red Light Improve Germination & Production in Tomatoes?. Visible white light can be divided into several colors, or wavelengths. These colors have varying effects on plant growth. For example, plants reflect rather than use green light, but red and blue light are both used for photosynthesis. Annual … ]]>