It’s a pretty logical thought right? A light that is 2000 lumens will be twice as bright as it’s 1000 lumen brother, so I’ll be able to see twice as far. Seems fair. However once we look into the reality of the situation, come to realize that it isn’t true. In fact in order to see “twice as far” you’ll need a light that is FOUR times brighter, or a 4000 lumen light using the same optics. Why is that? Pretty simple really. Math.
If you haven’t already, I suggest that you read our earlier blog post on lumens, lux, and candella HERE to get up to speed with the terminology.
It is a fairly commonly held perception that 3 to 5 lux is amount of light that the average person needs on an object in order to quickly and reliably spot it on either a trail or a roadway. This is a figure that is independent of distance. This covers everything from tree branches, to the trail, to road markings, other pedestrians, or parked cars even, simply just how much light is needed on a target.
So with that number in mind we can start to think about situations where we need that much light in order to light up something enough to recognize it quickly. Lets say you are riding with a 1000 lumen light (actual lumens!) and there was a big rock on the trail 50 meters in front of you, this means we need a light that can light up that rock with 3 lux of illumination at 50 meters. We can use some math to figure out how much candella, or light intensity is needed from our light:
Iv(cd) = Ev(lx) × (d(m))2
Iv(cd) = 3(lx) × (50(m))2
Iv(cd) = 7,500 cd
Now, we can think of candella and lumens as linearly related, i.e. lumens is like a volume knob for candella. Twice as many lumens will increase the candella of that point twice as much. Easy right? So now lets say you were riding with a 2000 lumen light, so your candella is now 15,000 cd, logic would dictate that you should be able to see that rock from 100 meters away now right? Well let’s look at the numbers:
Iv(cd) = Ev(lx) × (d(m))2
15,000(cd) = 3(lx) × (d(m))2
15,000(cd) / 3(lx) = (d(m))2
√(15,000(cd) / 3(lx)) = d(m)
d = 70.7 m
So instead of being able to see that rock from 100 meters out, you only gained a 41% improvement in actual spotting distance despite a 200% increase in the number of lumens in your light. This is part of why big lumen numbers are not key. What is more important is the quality of the beam pattern and how those candella intensities are spread out within your field of vision. These are not easy to report numbers, and have to rely more on wall shots and user reviews in order to figure out what is a quality beam pattern. If you see an ad for a light that doesn’t show exactly what kind of beam pattern you are getting, run away, proper companies that do the work for developing a proper light will be happy to show you wall shots showing off how smooth and well illuminated their patterns are. For example, here is the Trail Edition beam pattern, can see how radically different it is from the typical bike light found.
If you have any other questions, always feel free to start up a chat!
We have all seen it before, and maybe have fallen for the claims ourselves. The hundreds upon thousands of Amazon, eBay, Alibaba , Aliexpress, and even reputable suppliers who might not understand the specifications they are advertising. Of course we are talking about lumens!
It is hard to shy away from the allure of a seemingly incredibly cheap light touting 5000, 8000, and even 12,000 lumens for the low price of $40! With a single battery that lasts 3 hours, or even multiple battery packs that can do 8 hours! They must be true if all the reviews are good right? Well, not necessarily. However there is a pretty quick way to check if the claims are true if you can look up a few specifications.
Now, one thing must be made clear. Often these very cheap lights are claiming to use genuine CREE, Lumiled, or OSRAM chips. However, that is often not the case. Those chips can cost anywhere from $3 to $10 each for genuine, top-of-the-line components that are quoted in supplier datasheets. The business case simply does not make sense if a light uses 9 “genuine CREE” that cost $3 each, and they are selling it for $20, not including the electronics, the case, the optics, the body, and more. Often they are counterfeit components that do not produce anywhere near the claimed datasheets of their genuine counterpart, but they cost pennies, not dollars. Research has been shown that they produce roughly half the lumens per watt of what a genuine component does.
So what is a quick way to figure out how many lumens you really are getting? Well, often on most advertisements you will find how long the light is supposed to last, and with what kind of battery or battery pack. Let’s start with a typical listing, remember this is advertising the light head only, a battery is not included.
It is advertising 9000 lumens from 9 LED’s, and claiming to use CREE XML2. In a rarely seen move it actually has the amperage and voltage for the bike light supplied. So we can do a quick check of the wattage that the light requires to run on high mode:
1.2 Amps x 8.4 Volts = 10 watts
This next part disregards things such as thermal losses, electrical efficiency drops from the supplied wattage to the actual chip, and instead just focuses on the theoretical “best case” situation. CREE itself advertises the XML2 chip has having an absolute maximum efficacy (measure of how efficient light is) of 170 lm/W. These are often tested at very low watt conditions (where heat is the lowest) and using the highest grade of components that cost on the order of several dollars each. But lets assume that it is using that perfect CREE XML2 chip, with no power losses. That means at absolute maximum, it would be putting out maximum output of 1700 lumens. Which isn’t too bad for a $35 lamp.
But lets take it a step further, and figure out what the “real” lumen number would actually be.
First step is to figure out the efficiency losses from the input power to the chip itself. The best designed electrical boards using the highest quality components is around 85-90% efficient. Real world testing of other cheap lights have shown driver efficiencies of anywhere from 60-75%. So let’s run with 75%. This means the input wattage to the chips themselves is roughly 7.5 watts.
Now moving onto the chip itself. The real world efficacy is often measured to be around 110-120 lm/watt once things such as thermal losses, and lower grade bins are used. This is still assuming it is actually using genuine CREE chips, which you won’t know until you have taken the chip and put it under a microscope, part of why the rampant use of brand names is so prevalent. It is very hard to tell whether a chip is genuine or not until the product has been purchased, taken apart, and looked at by someone with a trained eye.
Now we take the 7.5 watts, and apply the 110 lm/watt to get around 800 real world potential lumens. These are the potential lumens upon startup when cold. Things such as thermal transfer, case design, solder joints and more will determine whether the actual 800 lumens will drop off significantly as the light heats up, or whether the light itself will fail due to poor design.
So we are at a real-world potential lumen amount of 800, or roughly 9% of what was claimed. Keep in mind these are just numbers that are pulled from supplied datasheets, or taken from numbers that are given by the seller, and assuming genuine components. Counterfeit components are often 1/3 to ½ the price of genuine, but also have 1/3 to ½ the performance, so if this light is using counterfeit components then have to weigh whether one still feels comfortable using a 400-600 lumen lighthead for the that price.
This brings us to the Outbound Lighting quality guarantee. We are technical engineering minded people at heart, and believe in being completely honest about lumen numbers, chips used, run times and more. Our lights are not the cheapest because we did not skimp on costs to save a few bucks. Instead we focused on bringing a cost effective, highly engineered lighting solution to you. Using genuine components that put out exactly what we say it does. We do not like using lumens as a method of rating a light because of the misconceptions it brings. Instead we prefer lux and beam widths. This is a true measure of actual performance of a light compared to the “potential” energy that lumens provides. We have a detailed blog explaining lux vs lumens vs candela HERE.
One item that comes up often in forums that we do like seeing, is that thermal is discussed! As many of you know, thermal control is very important for not only LED life, but also the optical output, color temperature, and overall reliability. This is also why we opted for a downward firing reflector as opposed to a typical TIR or reflector bowl since it would allow for more a more optimal thermal pathway from the LED chip to the incoming airflow.
The main LED board is separate from the control board and is monitored using a thermistor that is located near the chip. We don’t expect that when the light is in use that it will reach a thermal step-down, but of course need to plan for the worst if we want to have a reliable product. Many thermal simulations were run to decide on the final design. The beam pattern has even been designed such that it forces the user to partially aim the light “down” just slightly so that incoming air is hitting the back of the LED heat sink directly. Combine this design decision, with large die cut thermal interface material (not just globs of paste) that are sandwiched together by the magnesium die casting, and you end up with a very well designed, thermally optimized heat sink that is not only thermally efficient, but also very lightweight due to the magnesium material choice.
When using the included large thick silicone strap for mounting on the handlebar, you will notice that the mount itself has an integrated air scoop that helps force more cooling air into areas of the heat sink that otherwise would be hard for air to reach in a conventional manner. Again this scoop was thermally optimized for overall height, fins, and more to help achieve the final design.
LED’s themselves exhibit decreased behavior when the thermal load increases. This is often found on cheaper type of lights (across all industries, not just bikes) where after a while the color gets noticeably blue, or the brightness decreases. This is because the temperature at the LED die itself is getting far too hot and operating outside it’s designed temperature range. We are talking about temperatures in excess of 300°F! When we take apart cheaper lights we often find a very small thermal pathway exists for the heat to go from the LED to the outside of the case. Or the case itself does not have enough surface area to properly dissipate the heat.
So what to look for when choosing a light? In respect to thermal, look for a light that has fins that act as heat sinks, and if possible try and find pictures of the light taken apart and see if there is a large metal surface for the PCB board that has the LED on it. You’ll want to see thermal paste to help fill the imperfections between the surfaces and maximize the thermal transfer. When it comes to bright lights, it’s not just about the lumen number, but the proper thermal design will see to it that the light will work reliably for years to come.