[Scotch Thistle]

The spectrum of light from the sun changes throughout the growing season, in relation to how high it is in the sky. In the middle of summer, when the sun is at it's highest, we get the fullest range of light at it's most intense. As the year draws towards winter, the sun rises lower and lower. This shallower angle causes the different colours of light to be bent at different angles as it goes through the atmosphere, resulting in a light that is much higher in red frequencies than in blue ones. This is the same effect that causes raindrops to split white light into a rainbow.

So to summarise, if you show a plant a light source that is biased to the red end of the spectrum, it will think its the end of the season and flower / fruit as such.

[gremlin]

So to summarise, if you show a plant a light source that is biased to the red end of the spectrum, it will think its the end of the season and flower / fruit as such.

Plausible, but wont you also get red biased light in spring when the sun is lower in the sky too?

[toasted]

the compact fluorescent bulbs come in different wavelengths
cool white is the more blue type and warm white is more red, both will work, or the strip light type
ive grown allsorts under them
or if you want to cover more area you can use something like a 70 watt high pressure sodium light or metal halide
metal halide would be better for starting plants early
just have the light on for about 16-18 hours a day and it shouldnt cost more than a quid a week.

[gremlin]

HPS and other "professional" lights seem to cost the best part of a 100 quid, what with ballasts, reflectors and stuff.  Which is way out of my price range.

But a cool white strip light (with a RCD) sounds more like my sort of gardening

[toasted]

you can get a 70w hps from toolstation for £26.51 under the commercial lighting section

[mceuskadi]

I bought a 60w (energy saving bulb) grow light including reflector and hangers from ebay for £28.
Grow lights should be 6400K which equals daylight. Conventional 3000K lamps are too yellow. here some further reading on this toppic
The lamp installed at ~1.2m height will light an approx area of 1.5m x 1.2m.

I bought it because my flat is north facing and we have sunlight to our windowsills for as much as 1-2 hours per day. Our seedlings and plants are doing pretty well with the lamp.
Tomatoes are 40cm, courgettes got their first male flowers - both will move to the polytunnel next weekend.

[JayG]

My local weather stations records the intensity of the sun's radiation amongst other things, and at the moment (30th April, 0930 BST and sunny  ) it shows 554 watts/metre^2, and in high summer it easily exceeds 1,000 watts/metre^2.

That is a good clue as to why (apart from colour balance) that providing successful indoor plant illumination can be tricky, and also costly.

[toasted]

but light levels of bulbs are measured by the intensity at a certain distance, the smaller bulbs just need to be closer so will have less coverage