Sorry VV, typo. two 4' floro's.4" ?? ohh typo. He means four foot. The difference between the t's of the bulbs has to do with diameter. Each T is 1/8" diameter. T-8= 8x1/8" or one " diameter. Generally, the smaller the diameter the more efficient the bulb. Most 'Shop Lights, I have seven of them in use, are t-12's and not as efficient as the t-8's you have. Sorry I forgot, what was your question?? I'm assuming these are between 2 and four feet long?? VV