Electric-Light
Senior Member
Interesting technical facts you will not find in any manufacturers guides as it is harmful to sales interest.
You also have the chance to learn about constant current, variable voltage circuits in this thread if you're not already familiar with it.
Maintenance personnel are quite aware that T12 lamps light up just fine in T8 fixtures. It is true. Most T8 electronic ballasts wouldn't mind it either. It will work reasonably good if its symmetric (no different wattage or T8s and T12s mixed on the same ballast).
Ballast sees a 4' T12 lamp looks like a T8 lamp between 24 and 36". The wattage and lumens both drop. T12 lamps are rated 20,000 to 36,000 hours, although under driving them without providing cathode heater voltage is bad for lamp life. So the only real harm is reduced lamp life, but can still last thousands of hours and lets you trade down output and wattage just like an LED conversion. This can work out ok for over lit areas especially when you already have tons of T12 lamps or can get them for next to nothing. T12 lamps are not particularly inefficient when used with electronic ballast and range between 70-90 LPW. You just can't cry about it when the T12 lamps burn out in 4-5,000 hours.
120v 60W light bulb is also a 60W 0.5A bulb. A 60V 30W lamp is also a 0.5A bulb. In every day work, products are rated for parallel use and rated for constant voltage and amperage increases with added bulbs. This type of circuit is called "constant voltage, variable current".
Amperage rated lamps can be added in the chain link and voltage changes with wattage. So you may see a constant current LED ballast(driver) that says 1A 50W. 25-50W. This means it holds 1A within a range of 25-50v on output. If we know each LED is about 3.3v, you adjust the quantity to stay within the range while avoiding getting too close to either ends. The wattage of LEDs is determined by string length. This circuit is called "constant current, variable voltage"
Normal magnetic ballasts are designed for efficiency and can only hold a steady current over a small range and the ballast tend to only allow a narrow range of lamps. A neon transformer or a sign ballast is designed for a wider operating range and hold the same current over a much wider lamp voltage at the expense of efficiency.
T8 lamps are rated at the same mA from 24" to 96" lamps. Usually one ballast SKU can handle 24-60" and another SKU for 60" and longer.
Given the same fill gas and amperage, fatter lamp decreases voltage and longer length increases voltage. As you increase the lamp length, the wattage is increased proportionally and at some point it loses current regulation, drops out. If excess lamp length is used, it sometimes fries the ballast from excessive power draw. Ask any neon and sign lighting tech and he'll corroborate this. Low wattage T8 such as 25 and 28W 48" lamps accomplish lower wattage by dropping the voltage by tweaking the fill gas instead of raising the tube diameter that would increase the amounts of expensive phosphor blends coating.
A 40W T12 lamp operates at a lower voltage and higher amperage than a 32W T8.
When operated at the lower T8 amperage, the larger diameter operates at lower voltage than T8 and therefore lowers power usage. If you are using a 3,100 lumen 40W T12 lamp, the reduced output can be comparable to 1400-1500 lm range LED drop-in. :happyyes:
For those whose primary objective is "I want to lower wattage" and "enough light that feels bright enough" and don't care about measured readings, trying T12 lamps in T8 fixtures and discarding/replacing yellowed lenses could reach a very fast ROI if the original light level "felt" "exceedingly too bright". It likely won't reach the lm/W of today's LED lamps, but the reduction in wattage and output is IMMEDIATE. Just as in the case of LEDs, if you switch to a lamp with higher CCT, you maybe able to make it feel like it lost less brightness than it actually did
As the only downside, the lamp wears out significantly quicker because filaments are designed to operate at a certain amperage and when the current is reduced without giving some auxiliary cathode heater power, the electrodes tend to sputter away and blacken the lamp.
You also have the chance to learn about constant current, variable voltage circuits in this thread if you're not already familiar with it.
Maintenance personnel are quite aware that T12 lamps light up just fine in T8 fixtures. It is true. Most T8 electronic ballasts wouldn't mind it either. It will work reasonably good if its symmetric (no different wattage or T8s and T12s mixed on the same ballast).
Ballast sees a 4' T12 lamp looks like a T8 lamp between 24 and 36". The wattage and lumens both drop. T12 lamps are rated 20,000 to 36,000 hours, although under driving them without providing cathode heater voltage is bad for lamp life. So the only real harm is reduced lamp life, but can still last thousands of hours and lets you trade down output and wattage just like an LED conversion. This can work out ok for over lit areas especially when you already have tons of T12 lamps or can get them for next to nothing. T12 lamps are not particularly inefficient when used with electronic ballast and range between 70-90 LPW. You just can't cry about it when the T12 lamps burn out in 4-5,000 hours.
120v 60W light bulb is also a 60W 0.5A bulb. A 60V 30W lamp is also a 0.5A bulb. In every day work, products are rated for parallel use and rated for constant voltage and amperage increases with added bulbs. This type of circuit is called "constant voltage, variable current".
Amperage rated lamps can be added in the chain link and voltage changes with wattage. So you may see a constant current LED ballast(driver) that says 1A 50W. 25-50W. This means it holds 1A within a range of 25-50v on output. If we know each LED is about 3.3v, you adjust the quantity to stay within the range while avoiding getting too close to either ends. The wattage of LEDs is determined by string length. This circuit is called "constant current, variable voltage"
Normal magnetic ballasts are designed for efficiency and can only hold a steady current over a small range and the ballast tend to only allow a narrow range of lamps. A neon transformer or a sign ballast is designed for a wider operating range and hold the same current over a much wider lamp voltage at the expense of efficiency.
T8 lamps are rated at the same mA from 24" to 96" lamps. Usually one ballast SKU can handle 24-60" and another SKU for 60" and longer.
Given the same fill gas and amperage, fatter lamp decreases voltage and longer length increases voltage. As you increase the lamp length, the wattage is increased proportionally and at some point it loses current regulation, drops out. If excess lamp length is used, it sometimes fries the ballast from excessive power draw. Ask any neon and sign lighting tech and he'll corroborate this. Low wattage T8 such as 25 and 28W 48" lamps accomplish lower wattage by dropping the voltage by tweaking the fill gas instead of raising the tube diameter that would increase the amounts of expensive phosphor blends coating.
A 40W T12 lamp operates at a lower voltage and higher amperage than a 32W T8.
When operated at the lower T8 amperage, the larger diameter operates at lower voltage than T8 and therefore lowers power usage. If you are using a 3,100 lumen 40W T12 lamp, the reduced output can be comparable to 1400-1500 lm range LED drop-in. :happyyes:
For those whose primary objective is "I want to lower wattage" and "enough light that feels bright enough" and don't care about measured readings, trying T12 lamps in T8 fixtures and discarding/replacing yellowed lenses could reach a very fast ROI if the original light level "felt" "exceedingly too bright". It likely won't reach the lm/W of today's LED lamps, but the reduction in wattage and output is IMMEDIATE. Just as in the case of LEDs, if you switch to a lamp with higher CCT, you maybe able to make it feel like it lost less brightness than it actually did
As the only downside, the lamp wears out significantly quicker because filaments are designed to operate at a certain amperage and when the current is reduced without giving some auxiliary cathode heater power, the electrodes tend to sputter away and blacken the lamp.
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