Does artificial light make a difference?

[MrsCordial]

I've set out my seedlings and young plants on a table by a window that gets good morning sun, but on these dark cloudy days we've had lately they get nothing. The room has a central three-pronged light fitting that we rarely use because it's a bit brash and bright. Would the plants benefit from that, or is ordinary house bulb artificial light not much use to them?

[RaptorUK]

When using artificial light you need to get it close to the plant . . . the intensity decreases with the square of the distance . . . so a light twice as far away as another will be 4 times less light at that distance.

Inverse-square law - Wikipedia, the free encyclopedia

[MrsCordial]

The first part of that sentence was quite enough, thanks RaptorUk ;D

[Two_Sheds]

Household lights aren't the type of light required by plants, which need full spectrum: How to Grow Vegetables With Grow Lights: 10 Steps (with Pictures)

Office lighting is around 320–500 lux, while daylight is 10000–25000 lux, with sunlight being even more.

[MrsCordial]

Thanks. I had a feeling it wouldn't make much odds to them.

[Two_Sheds]

I've set out my seedlings and young plants on a table by a window that gets good morning sun

so only a few hours then? and none at all when it's dark & cloudy. You could be putting them outside on the best days (ie, not cold & windy) which will be better for them than indoors.

This pic shows 2 beans sown on the same day, one on a south windowsill, the smaller one on an east (morning sun only).

[MrsCordial]

Yes that's right - I know it's far from ideal. Originally I wasn't going to sow anything in cell trays simply because I don't have anywhere to bring them on, but in the end I couldn't resist. I'll get it right next year

The problem I have with outside is the wildlife (wild rabbits, hens) and the sheer volume of plants that I would be ferrying out and in every day. I have a bench by the front door that will take three kitchen trays worth of pots, so I put out the peakiest-looking most days and protect them with old window frames. Even so I found the hen perched on the bench trying to get at them yesterday.

[Kristen]

Putting a piece of white card (or polystyrene, but not kitchen foil) behind them will help - reflecting light onto the back of the plants.

The bit about the "Inverse square law" that you need to know is that a strip-light needs to be no more than 2" from the plant. The sorts of specialist lights favoured by Cannabis growers (such as Metal Halide) generate so much heat that they cannot be that close, and are typically 2' away from the plants (so cover a reasonable area, and will penetrate a decent amount of foliage). But you are unlikely to have one of those lying around in your house

Supplemental lighting definitely make a difference though, and I think it is well worth considering as an alternative to a heating a greenhouse - a growing lamp/lighting rig, in a centrally heated house, has all the heat it needs for free and I think the cost of lighting works out cheaper than heating a greenhouse - plus you might get poor quality light in a greenhouse in a bad Spring - like 2013 was - whereas light quality from supplemental light is excellent - and you can run it for as many hours a day as you like / want to afford.

I have grown Cannas (not Cannabis!!) from seed in mid winter and they were 5' high and flowering about 10-12 weeks after sowing them - just using a Metal Halide lamp. This photo was taken in November - about 8 weeks after sowing the seed

[Two_Sheds]

The problem I have with outside is the wildlife ...and the sheer volume of plants that I would be ferrying out and in every day.

Yes, the hardening off is a PiTA, but I stagger it so that not everything is in & out of the gh every day ~ I just put out the plants that look like being big enough to be planted out within a fortnight.


Have you considered a coldframe? (those blowaways are coldframes). You would just need to unzip or open the hatch to harden off, instead of carrying everything out of the house every day