Mr Gardener wrote:
|A couple days ago I made the mistake of putting my tomato seedlings out
|on a windowsill for direct sunlight, and a few hours later I discovered
|they were all withered. (We've had a lot of sunlight here lately in
|Portland, Oregon.)
|
|I immediately removed them, and enclosed them in a humidity-containing
|package (it used to be a doughnut package but I filled it up halfway
|with potting soil), and hid it away.
|
|The next day, 10% of the seedlings began to perk up again.
|
|If I buy a photometer, how much light should tomato seedlings be exposed
|to?
|
|Is the real problem loss of water instead of too much sunlight?
|
|You probably shocked your plants with the sudden bright light.

Well, yes, probably.

|Seedlings need time to acclimate to bright sun.

Are there any breeds of tomato that are less shockable than Beefsteak
or Roma?

|Try them for just an hour a day, doubling the time each day. And make
|sure they are getting enough water and food.

I was hoping that the tomatoes would thrive on potting soil and high
humidity.

|I can't imagine plants getting too much sun, as long as they are
|gradually acclimated. Considering your location, you have plenty of time
|to start over again, a few times.

Yes.

|Sow them in your humidity container and as soon as the very first bit of
|green appears, get them out of the humidity and into the light. Your
|bright window should be fine if done this way. Flourescent tubes an inch
|above the plants would do as well.

I have theory that Cool White fluorescent lights will work just as fine
as Grow Lights.

|No acclimatation needed. The humidity beyond this point is asking for
|fungus / damping off / weakening.

Argh! I was hoping the terrarium would be self-sufficient, and I could
just seal them off from the outside world.

|conditions.
|And you don't need a photo meter, unless you are a very serious
|photographer.

If I knew the amount of light that was appropriate, I could computerize
the setup.