Tech Tip: Split Testing BPF Headlight Bulbs (Halogen vs LED vs Incandescent)

Tech Tip: Split Testing BPF Headlight Bulbs (Halogen vs LED vs Incandescent)

Today’s tech tip is jammed packed with some awesome information that I can’t wait to share with you.

In this post I will cover not 1 but 2 topics all in reference to BPF headlight bulbs.

With the new 446LED bulb making its way into the market today we have found it very necessary to explain and test why LED's are the best all around bulbs for vintage British motorcycles.

Before we begin our tech tip post let’s go over some points that I will cover.


 Points Covering today


  • Common bulb problems
  • Introduction to the new British Pre-Focus LED bulbs
  • Explanation of BPF bulbs
  • Calculating Watts
  • Split testing
  • Split testing bulb review
  • Bulb notes
  • Final thoughts
  • Selecting your bulb

Common problems using incorrect bulbs

It’s 2018 and about 90% (educated guess) of vintage British motorcycles on the road today are still running incandescent headlight bulbs.

The other 10% is split between sealed beams and halogen bulbs

All are great bulbs that will provide you with as.much light as possible but there are some problems you may face when you choose to install some of these bulbs.

Often times sealed beams and halogen bulbs put a heavy load on your charging system that most stock EMGO or Lucas alternators struggle with. Especially for later models with turn signals and other high-load accessories.

Today's mentality is "I want more" out of an old system that just "works".
Back firing, batterys going flat and electronic ignition problems are all leading issues that one may face when you have fitted a bulb whether it is a halogen, incandescent or sealed beam and your stator couldn’t keep up with the power it was consuming.

If you happen to run a high out-put (200W / 20Amp) stator or a three-phase stator most likely these problems wouldn't effect you.

With all the modern technology today why not have something more for less?



In February of this year (2018) a new type of bulb was developed to cope with all the charging problems many experience today.

This type of bulb is called an LED. Not only are LED bulbs smarter, brighter, cooler, and convenient they also emit a brighter light with more than half the load from a traditional bulb.

What makes the new 446 LED bulbs “smarter” is the fact that they have an IC chip built in to allow this same LED bulb to work with 6V, 12V and 24V applications.

Still not convinced?

Further below we will put the new BPF LED bulb to the test so you can see exactly how much you are saving and also gaining.


What is a British Pre-Focus bulb?

Original Lucas bulbs and headlight units from the 1940's though the 1970's accepted what is called a “British Pre-Focus” bulb.

The British Pre-Focus bulb or better known as "BPF" bulbs are unique to what is now known as a classic automobiles and also classic motorcycles.



British Pre-Focus bulbs typically have a round base flange with a small half-moon shape locating slot to prevent the bulb from rotating and to keep the bulb holder lead contacts in the same position.

BPF bulbs rely on the base as the ground where modern bulbs use 1 of the contacts or prongs as the ground.

For example, an H4 bulb with a 3-prong adapter uses 1 of the 3 prongs as a ground or common wire.


Split test (Halogen vs LED vs Incandescent)

If you have seen our product listings on the new LED bulbs some may get the vibe that it’s all fluff..

It’s not..

Below I will explain to exactly why we recommend using an LED bulb by performing a few bench tests.

The 3 types of bulbs I’ll be using for this split test is a Lucas 446 bulb, an EMGO 446 halogen bulb (446H) and the new LED bulb (446LED).

I’ll be performing this test using a 12 volt sealed battery, positive and negative leads and (2) multimeters. The first multimeter is to measure the battery under load and and the second multimeter is to measure amps.

The goal of this split test is to record each bulbs amps to calculate the wattage and also recognize the draw that each bulb puts on ones charging system by performing a few simple tests.


Obtaining Watts

Watts = Amps X Volts Formula

Above is a simple formula which will help you obtain wattage.

To obtain wattage I must obtain the correct battery voltage, measure amps then multiply the battery's voltage to obtain watts.

Using the formula above is key to obtaining the correct data.


Test #1 - 446 conventional bulb


Testing A 446 Lucas Headlight Bulb With Multimeter

The first test I’ll be performing is on a standard Lucas 12V incandescent headlight bulb. This is the same bulb that was fitted to most British motorcycles during the mid-1960s through the late 1970s.

Test Bulb Rating Voltage Part Number
BPF Incandescent Bulb (Dual Filament) 50W/40W 12V 446 / 414

Using the formula to calculate watts I will take measurements and record what I find for this bulb.

This is what I have found…

Battery Voltage (under load) Amps Wattage
12.7V 3.02A (Low Beam) 38W (Low Beam)
12.7V 3.39A (High Beam) 43W (High Beam)


Test #2 – British Pre-Focus halogen bulb


446 Halogen Bulb Amp / Wattage Test

The second headlight bulb I will be testing today is a British pre-focus base with a halogen bulb.

This specific bulb was produced by EMGO a few years ago and fits inside any headlight housing that can except a British pre-focus bulb.

Test Bulb Rating Voltage Part Number
BPF Halogen Bulb (Dual Filament) 60W/55W 12V 446H


Using the same formula I will take measurements and record what I find for this bulb.


Battery Voltage (under load) Amps Wattage
12.63V 4.74A (Low Beam) 59W (Low Beam)
12.62V 5.20A (High Beam) 65W (High Beam)


Test #3 – British pre-focus bulb LED bulb


 LED Bulb 446LED Testing For Amps / Wattage


The British pre-focus LED bulbs are the newest types of bulbs on the market today.


They offer a bright and clean white emitting light along with less load on your charging system.


Test Bulb Rating Voltage Part Number
BPF LED Bulb (Dual Filament) 970lm / 510lm 12V 446LED


Using the formula further above I will take measurements and record what I find for this bulb.


Battery Voltage (under load) Amps Wattage
13.6V 0.22A (Low Beam) 2.992W (Low Beam)
13.7V 0.49A (High Beam) 6.713W (High Beam)


Split testing bulb review

All the bulbs tested today performed as they should - no surprises here.

Right off the bat I noticed that just putting a load on a fully charged sealed battery I saw the voltage drop especially when testing the 446H halogen bulb followed by the incandescent bulb then the LED bulb.


446 halogen bulb notes

I was very surprised that the EMGO 446H halogen bulb required much more draw than the incandescent bulb.

Granted the halogen bulb is the brightest of the 3 that we tested followed by the LED and incandescent bulb. The halogen bulb also has the highest load one could put on your charging system.

I found that if you where choosing the halogen bulb you would indeed want to consider upgrading your stock stator as opposed to the LED and incandescent bulb.


446 / 414 incandescent bulb notes

The 446 / 414 incandescent bulb (stock bulb) is ideal for those who are happy with a traditional bulb. There is nothing negative to say other than most would think the bulb is too dim?


446 LED bulb

The LED bulb is the ideal choice for everyday riders. Although the bulb is much brighter than a traditional bulb however it is not the brightest in the arsenal... but a big increase non the less is visually noticeable.

The 2 upsides to the LED bulb is the light improvement and the lower amps that it requires. Between the two this is the best all around bulb that should satisfy any vintage British motorcycle enthusiast seeking more light.

The 446LED bulb comes in positive or negative variations


Chart Comparisons

Here is a final chart showcasing each bulb together, I only listed the high beam for reference as I believe that is the most important.


Lowest to highest amps / watts draw chart

Test Bulb Amps( High Beam) Watts (High Beam) Part Number
BPF LED Bulb 0.49A 6.713W 446LED
BPF Incandescent Bulb 3.39A 43W 446 / 414
BPF Halogen Bulb 5.20A 65W 446H



Final thoughts



LED bulbs are definitely the way of the future. It's really nice seeing LED bulbs suited for vintage British motorcycles because it has less load in regards to the charging system but it also keeps us riders safe.

Before LED bulbs where introduced in our industry we had to settle with incandescent bulbs, sealed beams and halogen bulbs. Although all are great alternatives there are many factors in which take place when replacing or choosing headlight bulbs.

Not all bulbs are created equal. Those that have installed headlights that resulted in dead battery's or ignition issues know exactly what I'm referring to.

I personally believe the introduction to high put stators had a lot to do with the bulbs users where installing on there motorcycles.


Select your bulb

Now that you have seen all 3 bulbs in action, now is a great opportunity to select a bulb for your application.

Whether it is a BPF halogen bulb, BPF LED bulb or a BPF incandescent bulb - the choice is yours

Below I compiled a few links for you if you would like to order your own headlight bulb, just click on each title

446LED Headlight Bulb (6V / 12V) (choose positive + or negative - in listing)
446H Halogen Headlight Bulb
446 / 414 Incandescent Headlight Bulb


Thanks for reading today

I hope I was able to shed some light (no pun intended) on which headlight bulb you should install in your vintage British motorcycle.

We all can agree that the traditional headlight bulbs that where fitted to these old machines work but just don't "cut it" for today's world.

Having stronger, brighter and safer bulbs make your vintage Triumph, BSA or Norton that much better from the day it left the factory.

Should you have any questions please feel free to drop us a comment in the section below. We look forward to all comments and feedback.

Ride safe!


  • J. Moralee

    I have a BSA Bantam that is non electric (no battery) runs a Genie dc mag. Currently it has a BFP 24/24 watt headlight bulb 3 watt speedo bulb and I have converted the tail light to a take 1157 bulb and have put a 1157 led conversion bulb in it. So far everything works OK and The only drawback is that when the headlight taillight & the speedo light are on (hi or low beam) it doesen’t have enough watts to brighten up the brakelight, it does com on but not as noticibly bright as I would like it. With the headlight out thhbrakelight works

  • Conrad K

    A few points here. For anyone researching the comments.

    These are for positive ground bulb applications. However these bulbs are not polarity specific, so you can run them either negative or positive ground. This is why one person here was running his own wiring to LED lights (as long as they were not polarity specific).

    All BPF LED lights (available) are 6000k which is a very bright white/blue light. This is just a limitation of what is available. A comment saying that this light can be distracting, or could cause some rider vision issues – many drivers are not used to such a white/blue light at night. In complete darkness, the sharp contrast could make it difficult for oncoming drivers. (This is why the US did not allow these types of lights for many years, until recently.) The more we use LED lighting the more we get used to it so over time it will be less of a distraction. One point I would like to see changed (for the premium charged for these lights) IMHO a light made for old British bikes should be 4500k-4800k which is more of a natural white. (Direct sunlight is 4800k) You can search on this topic and it comes down to cost – most LED auto lighting is 6000k because it is cheaper to make.

    Someone commented on the bulb only being on high beam. I have this same bulb on two bikes. A Norton Commando and a Triumph Trident. The Trident (for some reason I am still working out) puts the high beam on the lower side of the bulb. I just swapped the bullet connectors around which put the high up top. I’m still working on my Lucas switches not operating properly however, so that could also be a factor. But that would at least explain why the light only functions on high beam. A side note is that I plan to wire my low beam as a daytime running light using a relay. It would be nice if there were a kit available for doing this.

  • John Hall

    There is a another element, that you do not address, practicality n’ the road @ night, dusk dawn whatever! The position is LED may be bright and visible, but when it comes to vision clarity and focus. LEDs are poor when compared to a incandescent BPF or halogen H4 light! They are also and can be distracting to the rider. LED light has more scatter and therefore can obscure as well as illuminate.

    They have been brought in partly for Political reasons to do with Energy use in systems and Safety aspects, that is visibility of the rider amongst traffic, this however is a different concept to the rider having good visibility of the roads surface and adjacent surroundings, whilst riding at low light levels.
    You may find that the case is, that you change to LEDs, then revert back to pre-LED system as not everyone’s eye sensitivity is suited to LED illumination. Riding at night with an Osram Night Breaker on my 80s Kawasaki proved to be safer useful application than my friends new LED system, through wider issues being factored in and not just brightness and energy usage considerations. Technical advances are good, but so is honesty in application of said developments. Update, your motorcycle to the strongest system possible and then test all the options!



  • Gregg staley

    A friend of mine purchase a LED Headlight bulb and it will not dim down I have been pulled over 2 times of not dimming my light. There is no difference Between the high beam and low beam the police tell me. How can I cut the candle power down on the low beam?

  • William I Adams

    This is going to be a little wierd, but I bought a pair of 446LED bulbs for my 55 MG TF where I’ve installed a pair of 7" Lucas lamps as driving lights. I’ve also found LED lights for the main headlights. Due to the original incandescant power draw, I had intended to install relays and separate, new wiring to the driving lights, but with the low current load of the LED lights, I can now run all four lights on original wiring without relays. I would, however, echo a previous comment and ask for a light output (lumens) comparison. Thank you for the excellent currelt load information.

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