I have a lighting rep that is telling me he has a 4' 2 lamp t8 surface mount fixture(4100 series lamps) that will produce the same amount of light as an existing 4' 4 lamp t12 34W cool white fixture. I don't see where he's getting the extra lumens from with just 2 tubes. Any thoughts? I'm finding the t8 lamps produce about 2800 lumens, not sure what the old t12's give out.
T8 vs T12
- Thread starter nizak
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ptonsparky
Tom
- Occupation
- EC - retired
He may also have better reflectors and lens. Depending on the T12 you have the Sylv cat I have lists them from 1656 to 2610 mean lumens.
ptonsparky
Tom
- Occupation
- EC - retired
yup. T8s from 1530 to 2945 per.
- Location
- Connecticut
- Occupation
- Engineer
I agree its probably improved reflectors, meaning a better coefficient of utilization, and also better ballast factors from electronic ballasts.
Using the zonal cavity method, the footcandles from a fixture would be:
FC= (lamps per fixt) x (lumens per lamp) x (coeffic. of util) x (ballast factor) x (maint. factor) / (floor area)
Assume maintenance factor is the same, and the room area is 100 sf.
Using T8 lamps with 2850 lumens, a ballast with a 1.18 BF, and assume a CU of 0.8,
FC = 2x2850x0.8x1.18/100= 53.8 FC
Using T12 lamps with 2900 lumens, a ballast with a 0.72 BF, and assume a CU of 0.6,
FC = 4x2900x0.6x0.72/100= 50.1 FC.
So, I'd say its feasible that a newer 2 lamp T8 fixture could outperform and older 4 lamp T12 fixture.
Using the zonal cavity method, the footcandles from a fixture would be:
FC= (lamps per fixt) x (lumens per lamp) x (coeffic. of util) x (ballast factor) x (maint. factor) / (floor area)
Assume maintenance factor is the same, and the room area is 100 sf.
Using T8 lamps with 2850 lumens, a ballast with a 1.18 BF, and assume a CU of 0.8,
FC = 2x2850x0.8x1.18/100= 53.8 FC
Using T12 lamps with 2900 lumens, a ballast with a 0.72 BF, and assume a CU of 0.6,
FC = 4x2900x0.6x0.72/100= 50.1 FC.
So, I'd say its feasible that a newer 2 lamp T8 fixture could outperform and older 4 lamp T12 fixture.
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