Don's bulbs
rare light bulbs and lamps
glossary of termsinformation
definition of: RE-RATE

What is RE-RATE?

Re-rating the specifications of a filament bulb by changing circuit voltage.


Have you ever wondered how a filament bulb would react to a different voltage than what that bulb was designed?

Any filament bulb (incandescent, halogen, etc...) can be re-rated by changing it's circuit voltage.

By applying a different voltage to bulb from factory design, the characteristics of that bulb will change, and can be calculated (estimated) by mathematical formula.

CAUTION: Just because you CAN apply any voltage, doesn't mean that it's safe to do so. Over-volting a bulb can be dangerous and cause physical bulb failure because of actual bulb construction; which electrically can't be calculated by re-rating formulas. Don't over-volt any bulb unless you know what you are doing, you take full precautions, and you accept full responsibility. Over volting up to 5% is fairly commonly done and typically within many factory tolerances. But, much more than that will certainly create issues that you will need to engineer around.

Applying a lower voltage will require less current (and use less watt energy), light output will be decreased, and bulb life will be increased. Less heat will be produced. Lumens per watt will be reduced. The output color becomes more yellow (kelvins lower). Additional safety concerns are typically not an issue when using bulb at lower than rated voltage assuming situation is fully safe when operated at full voltage. Keep in mind halogen bulb types will stop their halogen cycle if bulb glass cools too much.

Inversely, applying a higher voltage than bulb rating will use more current (and use more watt energy), increase the light output and decrease the bulb life. Lumens per watt will increase. Output color becomes whiter (higher kelvins) being less yellow. More heat and infrared will be produced. You will have to cool the bulb properly (typically air cooling or forced air cooling) and keep the glass temp (and base, contacts and socket temps) within safe temperature levels. If you are using halogen bulb types make sure you don't cool glass to much. You will have to take every safety precaution into account when increasing voltage beyond factory specifications. This includes but is not limited to all heat dissipations. And increased electrical load and heat of feeds, connections, switches, wires, and sockets.

CRI and Kelvins goes up when voltage increases, CRI and Kelvins goes down when voltage drops. I haven't taken the time yet to research the mathematical formula for these characteristics. If YOU know the formula please email it to me.

General lighting bulbs off-the-shelf are typically 10% plus/minus of their rated specs. Keep in mind the further you push voltage from rated specs error rate on re-rating will magnify tremendously. In special cases you might have to test measure and hand pick bulbs out of a grouping to find bulbs that match a specific desired characteristic trait.

Re-rating formula is based on typical average for many different filament bulb types, and is provided only as a basic guideline and starting point for your own research. For more accuracy, you'll have to take actual real world measurements.

Re-rating Formulas:

V = Application Voltage
V1 = Design Voltage

Re-rated MSCP = (V/V1)**3.5 x MSCP at Design Volts

Re-rated LUMENS = (V/V1)**3.5 x MSCP at Design Volts x 12.57

Re-rated HOURS = (V1/V)**12 x HOURS at Design Volts

Re-rated AMPS = (V/V1)**0.55 x AMPS at Design Volts


references to this page: CHARACTERISTIC CURVES, VOLT