Choosing a Flashlight for Mammal Watching

Choosing a Flashlight for Mammal Watching

This article describes some theory and the associated decision process towards my final choice of a flashlight for mammal watching; in my opinion the best compromise of weight, usability and high illuminance at a reasonable cost. Although opinions as to the optimum product will be personal, the information presented should be useful to anybody looking to purchase.

What Type of Flashlight to Buy?

The flashlight market offers a huge range of items ranging from the very small to the very large and in a variety of types. Realistically, for mammal watching only the HID (high intensity discharge) or the LED (light emitting diode) types are suitable and the vast majority of flashlights are less than excellent, in many cases poor, and often with overstated performance specifications.

HID lights are capable of producing very bright illumination and are used in e.g. aircraft landing lights and more recently, vehicle headlights. A number of manufacturers produce HID flashlights. As developments with LEDs have advanced, this technology has taken over as the better one for flashlight use, particularly as LEDs produce light at high colour temperatures whilst being quite efficient. In addition, LED light sources do not exhibit the annoying colour fringing seen with HID types. The Table below shows a comparison of HID and LED features based on experience with flashlights of both types:-


Comparison of HID and LED Flashlights




Illumination levels


Burn duration


 Variable and usually longer   

Colour temperature 



Light quality

 Some colour fringing


Variable output

 On/off only

 Several settings on most products

Beam pattern            


 Single or multiple

Bulb life

 100s of hours maximum

 ~ 50,000 hours maximum

Switch-on time


 Very fast




 Generally higher

 Generally lower


My 25W Xenide flashlight (Allsman Enterprises: served me well for a few years until the bulb ceased to fire up as inevitably happens sooner or later with HID lights. The cost of a replacement bulb from the USA was $110 plus shipping, VAT, and a tax collection fee. Knowing that these bulbs have a finite life anyway, their slow warm up time to full brightness – ca. 10 seconds, and having only one brightness level available, it looked as if it was time to discard the Xenide and move to an LED solution.

Lumens, Lux, and Light Levels

The market is full of flashlights claiming ever higher and higher outputs in Lumens; some of the quoted figures are true or nearly so but many are erroneous and much higher than actually achieved. The frequently specified output in Lumens is a measure of luminous flux, the total amount of light emitted from a source. Flashlight outputs range typically from a few hundred to several thousand Lumens. Depending on the construction of a flashlight, the total flux may be distributed over a larger or smaller area as a function of the beam pattern. Rather more useful for assessing the performance of a mammal watching flashlight is a specification for the illuminance achieved in terms of the quantity of Lumens falling on a given area. Unfortunately, such a specification not always quoted by the manufacturers but a figure expressed in Candela, if given, provides a good indication of illuminance.

Beam Pattern

This specification is an important one; it is the beam pattern that makes a large contribution to a good mammal watching flashlight. Broadly speaking, flashlights can be designed to illuminate a wide area (in the USA sometimes called a flooder) or with a narrow beam to concentrate on a small area (in the USA sometimes called a thrower). It is quite easy to produce a flood beam but considerably more difficult to produce a well defined narrow beam.

 The classic theoretical parallel beam is achieved by using a point source of radiation at the focal point of a parabolic reflector. In practice, many flashlight reflectors are not truly parabolic and a wider beam pattern is the result. In addition, no light source in a flashlight is a true point source. With HID units, light is emitted from a fair part of the bulb; LED units are better in that the source is still quite small, even with higher wattage types. The limiting factor with LED emitters is that as the power increases, it becomes much more difficult to remove the heat produced. Contrary to popular belief LEDs are not indestructible and if they are used at elevated temperatures for longer periods, their performance will degrade. All higher output flashlights have to provide some form of heat sinking, usually extensive finning around the head of the light and with matt black anodising of the aluminium case as this is a better radiator of heat. One trick used by several manufacturers is to combine several individual LEDs into one flashlight head. This greatly increases the output and the amount of light delivered but in order to keep the item down to reasonable dimensions, each reflector is necessarily far from the ideal shape and the overall beam can be diffuse. Thankfully, a good number of manufacturers specify the beam angle of their products.

Opinions will differ as to what is the best solution, but for me it was to find as tightly defined a beam pattern as possible, accepting that even then, there would be a certain proportion of light emitted over a wider angle. That meant a flashlight using only a single LED, therefore less Lumens than would be available than from a multiple LED unit but with a correspondingly higher illuminance on the target.


Making a Short List of Flashlights

This is really a question of some Internet trawling to see what is out there. Most of the flashlights have the basic characteristics in common – e.g. waterproof, carrying strap, etc. and I am listing only some of the more important comparisons here. All of these flashlights are incapable of running at full power for extended periods as they would overheat and the maximum outputs in Lumens usually can be sustained for only a few minutes before the thermal protection cuts in and reduces the output to the next lowest setting. My short list came down to these although there are other possibilities:-

Nitecore TM38


 Narrow beam – 4°

 Maximum 1800 Lumens

 High illuminance

 Built-in rechargeable 8-battery pack

 Built-in thermal protection

 Increased battery pack weight

 8 modes; 5 brightness levels

 Sequential button brightness switching

 Multi-function status display

 Filters not available

 Tripod mount          

 High cost

The Nitecore TM38 (Lite) is a smaller flashlight with identical performance but using only 4 x 18650 lithium batteries. This has the advantage of lower weight, smaller size and easily replaceable batteries whilst still offering plenty of burn time


Thrunite TN42


 Narrow beam – 4°   

 Maximum 2000 Lumens

 Very high illuminance

 Sequential button brightness switching

 Built-in thermal protection

 Filters not available

 6 modes; 5 brightness levels

 No multi-function status display

 Uses 4 x replaceable 18650 batteries

 No tripod mount

 Low voltage indication

 Some users have questioned build quality

 Reasonable cost

 The Thrunite TN42C has a rechargeable battery pack but is otherwise identical to the TN42


Fenix TK75


 Maximum 5100 Lumens   

 Wider beam – 11°

 8 modes; 6 brightness levels

 Moderate illuminance

 Uses 4 x replaceable 18650 batteries

 Sequential button brightness switching

 Low voltage indication

 No multi-function status display

 Tripod mount

 Filters not available

 Reasonable cost


Imalent DX80


 Maximum 13,000 Lumens

 Wide beam – 29°

 Built-in thermal protection

 Lower illuminance

 5 brightness levels

 Significant close flood lighting

 Uses 8 x replaceable 18650 batteries

 Sequential button brightness switching

 Multi-function status display

 No tripod mount

 Reasonable cost

 Filters not available


Acebeam K70


 Narrow beam – 5°

 Maximum 2600 Lumens

 Built-in thermal protection

 No multi-function status display

 7 modes; 6 brightness levels

 No tripod mount

 High illuminance

 No UK distributor

 Uses 4 x replaceable 18650 batteries

 Magnetic ring brightness switching

 Filters available

 Lower cost


A few notes on batteries. Most of these flashlights utilise 18650 type lithium-ion cells. These are widely available but come in an equally wide spectrum of quality. To obtain the best performance from these flashlights, high performance cells are required – ones capable of considerable current dumping capacity. The cheaper alternatives will more than likely not work as well, have a shorter life span and may in extreme cases blow up with catastrophic consequences; you will have seen the pictures. Likewise, a reliable and correctly matched charger is essential.

Lithium-ion cells hate being deep discharged and most, if not all reliably produced flashlights will contain circuitry to indicate and/or prevent the voltage from dropping too low, turning the light down or off. As a belt and braces precaution, you might source the type of 18650s where each battery has its own built-in semiconductor to prevent deep discharge – so called protected cells.

I am using Olight [] 3.6V HDC (high discharge current) cells rated at 3500mAh, 12.6Wh and capable of a 10A discharge current, but other similar batteries are available.

The Final Choice

Apart from the information on the manufacturers’ web sites, an Internet search will bring up a number of mostly USA based YouTube video clips in which very enthusiastic users purchase and compare flashlights. Some of these merely illuminate various objects in the dark but others go as far as measuring luminous intensity and provide real data. At any rate, these sources are useful when trying to choose a flashlight.

For me, the Thrunite TN42 came a close second on performance, value for money and on paper at least, it puts down the highest luminous intensity of the flashlights listed. The Nitecore TM38 Lite is also very well specified although costly.
However, in the end, it was the Acebeam K70 that I purchased. Not that it would have mattered had one of the other products been better, it was also one of the lower cost options. A key benefit of this flashlight over all the others is the magnetic ring brightness switching. Rather than having sequentially to half-press a button on the side or end of the light, the ring is rotated – clockwise to increase the brightness and anti-clockwise to decrease it – and it can be done using only one hand. This arrangement suits me but others may find the button alternative equally acceptable. The ring switch means that when you switch on the light using the end button, you can have pre-selected the brightness in advance. This is of considerable benefit on the lucky occasions where you are close to the target and do not wish accidentally to blind it or frighten it off with too much light. Most of the sequential button switching flashlights hold in memory the previous brightness setting so it is not as easy to pre-select a given level.

The other (unique?) feature of the Acebeam K70 is the availability of filters. These come in red, green or translucent and screw into the head of the flashlight. In contrast to some cheaper filters, the glass appears to be tinted rather than surface coated with a colour film; this makes it much more durable in use. When in a group with the usual poor levels of fieldcraft and lights flashing around everywhere, the use of the red filter is limited. However, on your own or in well disciplined company, it is a useful tool, albeit the filter induces some beam spread. The translucent filter is just a piece of ground glass which diffuses the beam. With the K70 wound up to high power, there is plenty of light for detecting eyeshine at night; the advantage being that a wide area can be illuminated at once from a moving vehicle with far less painting of the search area. If there is a downside, it is that the filters take a good 15 seconds to screw in or out when changing them.

Even with its narrow 5° beam angle, the Acebeam K70 exhibits some side spilling of light which interferes with night vision and also illuminates to some extent the operator or others in a group. I have made a modification which mitigates this effect by taking a filter, removing from it the coloured glass, then machining a short length (about 1½) of 3“Ø x 16 s.w.g. aluminium tube to fit back into the filter holder. The tube is powder coated black and matt black spray painted on the inside to absorb rather than reflect light. Screwed onto the flashlight head as you would the filter, this reduces the side spilt light without affecting significantly the light thrown forward.



Like almost every other similar product these days, the Acebeam K70 is manufactured in China and the build quality is very good. It has been used in several countries and a variety of situations, consistently out-performing flashlights used by others present. So far it has not given any problems and has produced no unpleasant surprises. A number of nocturnal mammals who might have thought they were safely beyond view have been spotted and I regard the purchase as having been well worth it.

There remains the difficulty that at the time of writing, there is no UK outlet for this product. The Acebeam K70 is available on mail order very easily from more than one source in the USA where shipping to any mainland location is usually f.o.c. Ordering for UK delivery will of course attract shipping, VAT and a tax collection fee. If you can find a way of having any of these flashlights delivered to a USA address and you subsequently go over there, you may bring it back into the UK quite legally within your maximum allowance of goods (£390 at the time of writing).


The usual disclaimers apply. I have no connection with any of the manufacturers mentioned in this article and do not stand to gain in any way from my comments or recommendations. I believe all that I have said here to be factually correct, but readers should check carefully on specifications and other data before purchasing and I apologise for any errors.


Chris Grimmett
January 2019


  • Stephen Babbs

    The Acebeam K70 is available on Amazon for £170.

  • mikehoit

    Thanks for posting this Chris, really useful. Cheers, Mike

  • Jerzy

    At least for German speakers, there are informative fora of flashlight enthusiasts, like They include practical photos of objects illuminated by different flashlights. I guess similar websites exist in English language, too. And no, I didn’t know there can be such a thing as enthusiast of flashlights, much less a group of them, until I found that site by chance.

    One practical parameter you are looking for is “throw” or distance to which the flashlight illuminates objects.

  • Olli Haukkovaara

    I am using Olight X9R Marauder, it’s really powerful and easy to use, max 25 000 lumen LED torch. It has actually 9 different modes from 200 lumens up to that 25 000. Warranty is 10 years.

    The beam is really wide so it’s easy to illuminate wide areas – and makes it easy to find mammals during night.

    It has smart output control to prevent overheating. Active thermal management system reduces the output when the temperature gets too hot to prevent any damage or overheating.

    Nice feature is the proximity sensors that drop the output automatically when the flashlight head approaches a nearby object.

    It is bit heavy but also ergonomic, it has milled finger grooves, shoulder strap and concealable strap hole for convenient and comfortable use.

    Currently the price varies between 450 – 600 euros.

  • Jens Hauser

    Hi, has anyone used the Acebeam K70 for photography?
    I mainly going to use the flashlight for photography and it looks kind of bulky.
    And it is very hard to buy from Sweden as well.

    • Chris Grimmett

      Jens – see my other post at which shows how I use this flashlight on a camera.

      The Acebeam K70 seems no more bulky than any other flashlight that uses 4 x 18650 cells and has a parabolic reflector. It is all down to how much light you want; there are many flashlight alternatives using fewer batteries and with smaller reflectors. If there is one which features a similarly high light output but which uses only e.g. 1 x 18650 cell then that would be interesting. Most manufacturers do not offer this as the burn time on such a flashlight would be considered far too short.

      I agree that the international distribution arrangements for these items are variable. Perhaps some of the other flashlights I shortlisted are more easily found in Sweden?

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