Purple tomatoe leaves

Hi all been growing my tomatoes in my grow area and when watering today noticed some of the leaves are turning purple
My set up is
Lights on 14hrs a day
Small oscillating fan
Water when top of soil feels dry
Temp when lights on around 25c and 20c when off
I’ve done a quick search on the net but it all saying to cold? Any ideas would be appreciated
Thanks all

 

This happens with many varieties of tomatoes grown solely under artificial lights.

Yours don't actually look too bad, are they under T5s or LEDs?

This is how 'blue' some of my toms got under T5 lights before I moved them to get a mix of natural daylight and LED light



If permitted to continue growing like that, the leaves can develop white, thin, scorched patches.

 

They are t5 the plants are under 9 6500k ones what would you recommend I do

 

Get them into some natural daylight, or if that's limited, a mix of natural daylight/cool white LEDs.

But they don't seem too bad to me.

Which variety of toms are they?

 

From your photo Notty I think yours look fine, nothing to worry about. I do as Scrungee says, get them out during a mild day for some proper sunshine.

 

I’ve got 4 different types in there
Alicante
Gardener’s delight
Money maker
Beef master
As well as
Cucumber
Chilies
Peppers
Would a west facing window sill be ok the heater for my greenhouse hasn’t come yet so still to cold at night in there for them

 

My T5s (that caused that discoloration in my toms shown above) are only on for 10 hrs/day, mainly because I have Economy 7 tariff electricity (on 21:00 to 7:00) so I can almost halve my lighting costs by running them on the low overnight rate, but also supplement the artificial lighting with some free light by relocating any plants appearing to suffer from artificial light/needing a supplement inside a window during the sunny part of the day.

 

The purple colouring in the leaves and/or stem indicates that the intensity of UV light is too high for the young and tender seedlings.

The built-in sunscreen kicks in and slows down chlorophyll production which in turn slows down growth due to reduced absorption of energy through photosynthesis.

Essentially, growth is halted until conditions are right. When the conditions are right, the leaves turn back to green again.

In the OP's case, it is probably temperature related (maybe a cold draft?).

In their native environment, seeds would germinate and grow under the canopy of the parent plant from fruit (a tomato) that has fallen onto the ground.

So, it's in the tomato seedling's DNA to expect partial shade early on in its growth, anything different would trigger their self preservation purple sunscreen mechanism.

 

Brill thanks for all your help everyone