[Hadakare]

Got some seedlings coming up  on south facing window sill. As they lean towards the sun, Curious to know if turning them round on a a daily basis  would strenghthen them or weaken them?

[Yorkie]

Turning them will be better than not turning them.

Put foil behind them to reflect light back onto them.

Chances are that they will end up weak and spindly at this time of year though.

[Goosegirl]

As Yorkie says, they may well grow spindly because plants grow towards the light (phototropism) and, if the light isn't strong enough, it just "pulls" their growth.

[Kristen]

Light through a window is nothing like as good as light through a greenhouse

And light in February is not nearly as "good" as light in March

Definitely put something reflective behind them. I have read that Kitchen foil is not as good a reflector as somemthing flat-white - such as a piece of Polystyrene, or even a piece of white card.

[JayG]

Definitely put something reflective behind them. I have read that Kitchen foil is not as good a reflector as somemthing flat-white - such as a piece of Polystyrene, or even a piece of white card.

Presumably wasn't this thread you read then Kristen: 

http://chat.allotment-garden.org/index.php?topic=118034.msg1377666#msg1377666

If you pasted the aluminium foil onto a flat board it could potentially reflect some of the light away from your plants, so it's best to curve it slightly round the plants (room side only, of course), shiny side facing the plants/window.
No need for any fancy mounting or supports, it's cheap enough and can be screwed up and recycled when done with.

Any reflector will be better than no reflector. 

[Kristen]

Interesting thread, but no it wasn't that one. The one I read was on a Cannabis forum (high value crop sharpen's their minds on maximum efficiency I reckon?!!) regarding some scientific research that had been done into reflectivity, particular somewhat crumpled kitchen foil, which carried a risk of hot-spots as a result

Like anything on the internet could be mis-quoted of course.

[surbie100]

If you put something behind the foil to prop it up, make sure it's either not water absorbent or not touching the bottom of the tray. I put card behind my foil, then watered my seedlings from the bottom. The card promptly soaked up the water and fell over....

[DD.]

Foil is simple. You can tuck it under your trays and bend it upwards. with a quick nip and tuck it is self-supporting and re-usable.

Have a look at this science experiment for schools. It compares various surfaces to aluminium foil.

The sample results give the relectivity of white as 78.9% of that of aluminium foil.

http://www.wsanford.com/~wsanford/gr8ps/zz_old-files/yellow/radiation_station/reflectivity-of-light_23.pdf