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What Determines The Brightness Of The Bulb?

When purchasing a light bulb, specific specs are pretty straightforward!

The color temperature depends on the Kelvin scale, the color rendering depends on the CRI.

But something as simple as brightness is not just looking at Lumens and being done.

Other factors can also affect brightness, such as voltage and current.

The brightness of a bulb depends on both current and voltage depending on whether the bulb is in parallel or series. The type of bulb and the light output ratio of the fixture will also determine the total brightness.

Voltage vs Current vs Wattage: What Affects Brightness?

First of all, the bulb’s brightness, light (and heat) energy, depends on the power being input into the bulb.

And power, measured in watts, is the voltage and current product, that is, power = Voltage x Current, P=VI.

So technically speaking brightness depends on both voltage and current.

An increase in either voltage or current will increase the brightness of a bulb. In incandescent bulbs, this is the case.

But technically speaking, you cannot usually increase current at your end. Still, you can sometimes increase the voltage, allowing more current to flow in, and in turn, the power or brightness.

When the brightness increases, this also means that the filament’s temperature inside an incandescent bulb also increases.

However, the bulb will only get as bright as the maximum voltage allows. If you turn up the voltage higher, the filament will overheat and fuse.

This maximum specified voltage allows the incandescent to work at its brightest possible. This is called the operational voltage.

On the other hand, of course, decreasing the supplied voltage will dim the light bulb. This applies to bulbs in series and parallel.

In LEDs, the story goes a little differently. LEDs are not designed to run at varying voltages, but you can vary the current instead.

This is because changing the voltage even slightly shoots up the current rapidly, increasing the brightness in turn. This can damage the LED.

By varying the duty cycle of constant current through the pulse width modulation (PWM) device, you can achieve more accurate changes in the brightness of LEDs.

And while you can reduce the voltage, meaning the LED will have lower brightness, that’s not required.

But similarly, raising the voltage higher than the specified fixed voltage will damage the LED. Basically with a high voltage the LED will burn bright for a little while, then turn slowly, get darker, and get damaged.

Does Brightness Depend on Resistance?

When it comes to affecting brightness, another factor plays heavily into what makes a bulb shine brightly or dimly.

An incandescent bulb’s brightness depends on a whole lot on resistance. The higher the resistance to current in the wiring, circuitry, and bulb, the lower will be the current, lower the power, and lower the brightness.

Conversely, lower resistance means more brightness.

When an incandescent bulb turns on, the filament’s temperature is low, meaning a low resistance, allowing an inrush of current.

So the first split second of a traditional bulb is dim. It immediately gets to full brightness as the filament temperature rises, and resistance also increases.

This immediate higher resistance allows a drop in the current. It regulates the current to an equilibrium, or a stable circuit, running your bulb at the standard current.

Also read: Do Incandescent Bulbs Heat Up A Room?

Resistance in the bulb can come from the filament, the wiring, actual resistors in the circuit, and any other metallic components. In fact, the bulb itself is also a kind of resistor.

Therefore, it is vital to have good quality wiring inside the home and office space to have maximum brightness and least energy wastage in overcoming the resistance.

The material used and the thickness of wires all have an effect on resistance and subsequent energy wastage. You cannot go wrong with high quality wires.

Is Brightness Affected When Bulbs Are Connected In Series And Parallel?

The goal should be to set up electrical components, appliances, and lights in the most energy-conscious and smart way possible.

This means choosing between setting up your circuits in parallel or series. Only one of them is the right way to go.

When you connect bulbs in parallel, the voltage across each individual bulb in the circuit will be the same as the power source.

Therefore their brightness will also be the same, and they will all be equally bright or dim, powered by the same source.

This is the better way to wire bulbs and appliances in the house, so the same amount of voltage and power reaches across the electrical network.

Another interesting advantage of having bulbs in parallel is that if one bulb in the circuit burns out for any reason, the rest of the bulbs will still work because they are as if they are directly connected to the power source.

For example, festive string lights are made by joining a set of bulbs in series, parallel to each other. So when one bulb goes wrong, the neighboring 5-10 bulbs also stop working, but the rest of the string continues to work.

In series, however, light bulbs share the same current. So they split the available voltage into the number of bulbs in the series circuit.

As the voltage available to the bulbs goes down, so does the power since P=VI. The brightness, in fact, goes down increasingly with each added bulb in series.

And again, bulbs in series are all part of the same circuit, and when one goes down, the whole circuit goes down with it.

So if you have the option, definitely set up lights in parallel, even though it requires more wiring and more managing of the wires.

What Other Factors Affect Brightness?

Other, less apparent factors also affect your bulb’s brightness at the end of the day. A lot depends on the fixture and the designing of the bulb itself.

Firstly, the positioning of the fixture is a straightforward yet impactful difference. The higher up your fixture sits in the ceiling, the less bright it will seem. The light beam becomes more concentrated, and thus brighter, the lower the fixture gets.

Another less obvious specification you might want to consider is the light output ratio (LOR), which tells us what percentage of light gets lost inside a fixture.

You want to consider a fixture with a high LOR percentage, so use your bulbs’ brightness and electricity most efficiently.

Secondly, since incandescent bulbs reflect light in all directions, even where not needed, they sometimes use reflectors to direct a beam of light to an intended area.

But using a reflector also translates to light output losses each time the light reflects inside the bulb, anywhere between 10-30% of the loss.

On the other hand, LEDs give out directional light, and when needed, can be made to give light in 360° using corn bulbs or globe bulbs.

So keep the beam angle and use of unnecessary reflectors in mind when considering a new bulb.

Finally, the most important and also obvious number you need to look at is, of course, the Lumens, which is the measure of the lumen flux of light. This will accurately tell you how bright the bulb is.

Final Words

As you can see, there are a lot of things that contribute to the light bulb brightness. The bottom line is that lumen is not the only thing that contributes to that.

You should always look for the light output ratio of the fixture and the size and the height of the fixture on the ceiling.

Have you tried to set up your lights in series or parallel?

Do you know what the material of wiring inside your home or office is?

Let me know in the comments down below.

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