T5HO VS T8 Lighting Fixture?
T5HO VS T8 Lighting Fixture? Because this questions is asked so much I will try and explain it as best as I can. I will explain size of lamp (Bulb), wattage of each lamp, lumen output, energy savings and equivalent lighting fixture “i.e. how many lamps are equal to same output.
First, size of lamp T5’s range in size as well as do T8’s, but for this article I will be discussing T5HO’s and T8’s for 4 foot fluorescent fixtures. T5 or T5ho’s are measure in metrics and are slightly shorts then 4 feet or about 46 inches long. When buying a T5 fixture usually the fixture will measure 4 feet and the difference in size of the lamp will be made up by a extended sockets. On T 8 lamps the lamp measures from end of the pins 48 inches altogether and will fit a 4 foot fixture perfectly. The diameter of the lamps very T5 are 5 tenths of any hence the 5 in t5 and t8s are 8t tenth of an inch.
Next wattage, again several T5s out there varying in sizes which also vary the wattages for the lamps. T5 4 foot lamps vary from 28 watt non high output to 54 watt High output and the new 49 watt t5 or T5HO lamp. T8 lamps also vary wattages from length. Lamps for a 4 foot light fixture range from 24, 26 watt reduced energy bulb to 32 watt standard output which lumen output is controlled by the ballast.
This brings us to lumen output
T5 28 watt lamp equals about 2800 Lumens per lamp position
T5ho 54 watt lamp equals about 5000 Lumens per lamp position
T8 32 watt with a low power factor ballast equals about 2100 to 2300 lumens per lamp position
T8 32 watt with a normal ballast factor ballast equals about 2500 to 2700 lumens per lamp position
T8 32 watt with a high ballast factor ballast equals about 2800 to 3000 lumens per lamp position
To answer the energy savings question from the research that I have see, head to head, lumen to lumen equality vs. watts output the t8 fixture for the same amount of lumen is more efficient by about 3 percent .
So with this all said here is your fixture break down:
4 lamp 54 watt T5HO fixture equals 20,000 lumen output one to one swap with a 6 Lamp high ballast factor T8 32 which equals 18000 lumens watt fixture this is comparing a high bay fixture. 6 lamps T5ho fixture approximately equals the output of a 400 watt metal halidewhen new before the 3 year diminish.
Please Let me know if this help clarify this!
James Abraham
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Industrial Light Fixtures & Lighting For The Future 
i love your site. thank you so much!!
Hi James Actually it is measured in 8ths of an inch. T-5= 5/8″ dia., t-8, 1″ dia, R30 = 3-3/4″ (30- 8ths) t-12, 1-1/2″, (12-8ths). This is what GE told me years ago. At least those are the measurements of my Philips, GE and Sylvania lamps. The rest of the info is great. Thanks.