T8 four foot tube problem

[Hybridowner]

I've had six T8s replaced lately. Same tube markings as old tubes, but the new ones are dim when first turned on and take 3-4 minutes to get up to full brightness. Turning them off and back on 15-20 minutes later and they start out bright. Changed ballast on one fixture and that made no difference. Why is this happening? Somebody's "save the environment" idea? Thanks.

[barry2952]

Probably a lower mercury level. Try a different brand. All gas-type lighting has a warm-up time. Some of it is temperature related.