Xtar’s current top of the range model in output, size and weight is the S1 ‘Search and Rescue’ light. In a format that is becoming increasingly crowded, the S1 uses three XM-L U2 LEDs, so will it earn a place in your line-up of lights?
Substantial, solid and serious are the first words that come to mind. As you take the S1 out of the box, it feels heavy. Many manufacturers are slimming down their lights while bringing up the performance, the combination of which are a lot of lights that get very hot as there is not much substance to them. The S1 has the performance, but also has the heft to easily cope with it day-in, day-out.
Many industrial products have a ‘duty cycle’ rating (a machine's rated capacity to continuously perform work under normal conditions) quoted in a variety of ways. It would not surprise me if the S1 were to have a duty cycle of 100% (continuous maximum output) as it seems built to take some serious use.
What is in the box:
The large box is plain cardboard with black printing directly onto the card. No frills, but neat.
Inside is a closed cell foam liner holding the S1 firmly and providing excellent protection. The S1 is supplied with spare o-rings, lanyard, instructions and a draw string fabric storage bag, with black flocked outer surface and plain weave inside. As flocking has a tendency to loose fibres, it is good attention to detail to not use this on the inner surface of the bag, on it looks great on the outside.
The S1 out of the box
Taking a closer look and looking inside:
Multi-emitter lights combine the LEDs and reflectors in many different ways. The S1 has a single reflector, in a single housing, but this reflector is made up of three overlapping reflectors. This arrangement creates a little ‘spike’ of reflector in the centre where the reflector profiles intersect.
The tail of the light has a sizable set of anti-roll/grip features, giving you plenty to hold onto when taking of the tail-cap and keeping the light stable if placed on a flat surface.
The grip of the S1 has excellent grip, with knurled panels and ridges machined along and around the battery tube.
The machining is very crisply and accurately executed, and the complicated shaping of the tail-cap appearing flawless (please excuse the odd speck of dust).
The control ring is finished just as well as the rest of the light, with the grip depressions consistent in depth and spacing. The etched pointer can be seen lined up with the off position. There is no discernible play in the ring which feels very smooth in operation. The only play being in the detent positions which have a little movement side to side.
Opening up the S1, here the battery tube has been removed. This is not the normal way to use the light, as the batteries are replaced via the removable tail-cap. The large round positive plate can be seen clearly set into what appears to be white nylon (or similar polymer).
The battery tube has very thick walls and a triangular shape internal shape to support the three 18650 cells the S1 uses.
The tail-cap has an excellent design feature. The three contacts, as a group, are free to rotate within the tail-cap. Each contact has a polymer ring around it which is the same diameter as an 18650 cell. As the tail-cap is fitted to the battery tube, the three contacts fit into the corresponding shapes in the battery tube. While you screw on the cap, the contacts remain static and simply press down onto the cells themselves. This means that the cell contacts are not subjected to any rotation or scratching/scraping against the terminals.
The threads are crisp and fully anodised using a trapezoid shape. At the head end, the threads are bare aluminium and there are two o-rings. The tail end has only one o-ring fitted, but appears to have a second unused o-ring groove.
Looking deep inside the compound reflector shows the three XM-L U2 LEDs
Modes and User Interface:
There are four ‘on’ positions selectable via the S1’s rotating control ring. Two are to the left of the ‘off’ position, and two to the right.
The first mode to the left is High (100% output), and beyond this is the Strobe.
Moving the control ring to the right, first is mode is the user pre-set, and beyond this the selection mode.
The pre-set mode allows the user to store their preferred output level for immediate access. This is achieved by entering the ‘selection’ mode where the S1 ramps the output down and then up going between maximum and minimum output. To store the output level you want, simply turn the control ring back to the pre-set position once the output is at the level you want.
During the selection ramping of the output, the S1 pauses briefly at five different levels, Maximum, Minimum and three levels in between (the actual levels are listed in the next section). By eye, it is difficult to see the intermediate levels that are briefly stopped at, but it is easy to catch the maximum or minimum levels before the ramping starts again.
Batteries and output:
Powered by three 18650 cells. As the cells are used in parallel, if necessary, the S1 can also run on two, or even one 18650. If using less than three cells, the S1 may struggle to provide full output as the one or two cells used will need to provide all the required power.
To complement the S1, it was supplied with the separately available Xtar WP6 II charger (reviewed earlier – see my review list for details) and Xtar 3100mAh 18650 cells. These cells are some of the longest protected 18650s, but the S1 easily accommodates them.
To measure actual output, I built an integrating sphere. The sensor is a photo-diode restricted to visible light only (so Infra-Red and Ultra-Violet will not register). This was chosen as our eyes can only use the visible wavelengths of light so this is generally the only useful output. The integrating sphere was calibrated using 12 different reference sources and taking an average of the factor used to convert the measured voltage output to Lumens. Output figures are quoted as ANSI lumens where the measurement is made 30s after turning on the specified output level. Initial figures when first switching on are always higher, but all quoted measurements are ANSI.
Please note, all quoted lumen figures are from a DIY integrating sphere, and although every effort is made to give as accurate a result as possible, they should be taken as an estimate only. The results can be used to compare outputs in this review and others I have published.
Xtar S1 I.S. measured ANSI output Lumens PWM frequency (Hz) High 2174 N/A Ramping Pause 1 1623 470 Ramping Pause 2 1093 470 Ramping Pause 3 546 470 Low 17 470
The levels listed above are ANSI, but the Xtar S1 manages 2252lm at switch on.
The strobe output is at 9.8Hz. All output levels are provided by PWM apart from maximum. Watching the oscilloscope as the S1 ramped up and down in brightness showed the PWM frequency of 470 Hz remain absolutely constant, with the pulse width simply increasing or decreasing. As the output ramped up, the pulse width expanded until the output became constant.
Output is regulated and as the batteries become depleted, the S1 eventually drops out of regulation and the output then gradually declines.
The following photo was taken when trying to capture the LEDs at their lowest output. The exposure setting was f/8 ISO 400 1/3200, and at this shutter speed it no longer reduced the apparent brightness of the LEDs, as they were either captured while on or while off. The pulse width was very narrow, so the momentary brightness quite high.
In The Lab
In an attempt to quantify the actual beam profile I developed the following test. There are probably many flaws in my method, but it is simple and easy to carry out and seems to provide a good enough comparison.
The method used was to support the light 1m off the floor and 1m from a wall, with a tape measure on the wall. The zero of the scale is placed in the centre of the hotspot and a lux meter is then positioned at points along the scale, with the measurements recorded. Beam shots are often taken with the light shining on a flat white wall, so this method is simply measuring the actual intensity across the beam on a flat surface, not the spherical light emission.
The results are then plotted on a graph.
For the best throw you want to see a sharp peak with less of the distracting spill. For the best flood light the trace should be pretty flat.
The Xtar S1 beam profile is shown here compared to the Fenix TK41 as this is a well-known high performance light.
The S1 has a very sharp peak, just as a search light should, however it also has a smooth transition into a nice bright spill area. It is one thing to have a good throw, but if you then spot what you are looking for al a long range, without the good spill light as well, you may lose sight of it too easily. The S1 has this covered.
Taking this a little further, I calculated an approximate factor to apply to the lux measurements, as each measurement gets further from the centre of the beam, it corresponds to a larger area onto which the light is falling. It seems to me that this should also be taken into consideration, so I applied these area corrections and came up with this odd looking graph.
The key quantity here is the area under the graph line. This should correspond to the total light output.
This shows just how much light the S1 outputs, and it overwhelms the already impressive TK41 in all areas.
The previous beam profile graphs, show the S1 as having a refined smooth beam profile. Unfortunately, the compound reflector and multiple emitters mean the outer edge of the spill beam is a little messy and gives it a flower like appearance. That said, it is only the outer spill, within this is a good smooth round spill area surrounding the very strong hotspot.
To give a comparison of the S1’s powerful beam, here I’m comparing it to the Fenix TK41 as this is a known top performer.
Starting in the back garden with the TK41
And with exactly the same exposure, the S1
Then off to a tree lined track. The bend in the road that can just be seen in the distance is 150m away. First off, the TK41
Again with the same exposure, the S1. The spill is narrower, but overall everything about the S1 shows significantly greater output.
The beam is more throw than flood, and throws a great deal of light.
What it is really like to use…
This Xtar S1 is one of the most solidly built lights I have come across. The build leads to two main user experiences, the first being that it is heavy and not a light you would want to carry in your hand for extended periods (in my opinion). The second part to this though, is that the extra mass means that it runs very cool, even when on maximum output for extended periods.
Many other lights become worryingly hot when used at 100% output, but not the S1, it merely seems to be ticking over, and yet is outputting nearly 2200lm. This gives you real confidence that you can use all the output on offer with no step down or overheat protection jumping in and cutting down the output.
The simple user interface with only four selectable options, is all you need, although I would have preferred maybe two user pre-set levels, as I have been using the one pre-set on the minimum output level, so like this, if needing more light, you go from 17lm to 2200lm! However this light is a searchlight and will be coming out when you need (or just want) a lot of light.
Here the Golf Range club house is 100m away and appeared lit up like daylight.
Heavy duty and hard hitting, the S1 does live up to its ‘Search and Rescue’ claim, though I suspect most S1’s will not be used for rescuing.
Test sample provided for review by TorchDirect.