2024-03-16
After several years on the market, the XHP35 received an upgrade. The latest LED chips and the latest production technology have been used, which should improve performance and also increase efficiency. This test will show how strong this effect is.
The emitter tested here was regularly purchased from Mouser at the beginning of 2023. According to Mouser, the date code of this LED is February 16, 2022.
Tj 85 °C, If 350 mA
- Type: multi die, flip chip
- Bin: D4 (min. 550 lm)
- Color group: E3 (5000 K)
- CRI: min. 70
- Rated voltage: typ 11.2, max 12.2 V
- Max. Forward current: 1500 mA
- Max. Peak current: — mA
- Viewing angle: 120 °
- Thermal resistance: 0.7 K/W
- Max. Temperature Tj: max. 150 °C
Datasheet can be downloaded here: Cree XHP35.2 HI (PDF, 3 MB)
In principle, the XHP35.2 HI is similar to the old version. Here too, the luminous surfaces sit on a dark gray substrate and are surrounded by white potting compound.
What is striking about the successor generation is the absence of the bonding wires and the fact that the illuminated surfaces are at least apparently further apart, which is characterized by “gaps”. The yellow illuminated area also appears to be slightly smaller in direct comparison. The old XHP35 uses two different LED chips, flip chip and lateral, which massively increases the cost of the old version. The new XHP35.2 has only one type of LED chip, which is only connected from the underside.
In the side view, the phosphor below the white potting compound appears to have been applied over a large area on the entire substrate instead of just on the LED chips, as a thin white layer can be seen above the yellow layer.
The footprint offers no surprises. The edge in the thermal pad indicates the anode. Such significant reductions in the heat dissipation surfaces should be viewed critically; they further reduce heat dissipation, which is already severely limited, especially in the compact 3535 format. A marking on the top or a beveled corner of the anode is more advisable here.
The thermal pad is electrically neutral, so that the use of DTP aluminum and copper boards is possible without any problems without having to operate the LED in direct-drive mode (connection directly to the battery without driver electronics).
The illuminated surface consists of four individual LED chips. These are arranged accordingly on the substrate for 4S wiring. As is usual with most modern emitters, the chips are designed as flip chips.
The luminous area is 4.95 mm² in size. As the illuminated surfaces also emit light from the side, as shown in the image, it is difficult to determine the size of the illuminated surface using conventional methods and is not 100% possible.
Due to the relatively uniform illumination of the surface despite the gaps between the LED chips, no donut holes or “crosses” should occur in the light image when using secondary optics.
Within official parameters, as far as known:
- at 1,500 mA (official maximum current): 1820 lm @ 13.84 V
- Power at official maximum: 20.8 W
- Efficiency at 1,500 mA: 87.7 lm/W
- Maximum reached at 3.2 A, at this point 2485 lm @ 15.91 V
- Power at maximum 50.9 W
- Efficiency at maximum 48.8 lm/W
The D4 binning specifies a minimum of 550 lm at 85 °C. As the loss of luminous flux at 85 °C starting from 25 °C is around 10 % and Cree only allows a tolerance of +/- 7 %, the binning is not complied with and therefore corresponds to D2.
In contrast, the Vf of 11.64 V at 350 mA (binning conditions) is within the expected range. Taking into account the temperature coefficient of -5 mV/°C, the Vf at 85 °C is therefore around 11.35 V and therefore corresponds to the typical forward voltage.
With the XHP35.2 HI, overcurrent is only worthwhile to a limited extent. Although the luminous flux increases by 27 % from the permitted maximum, the output increases more than twice as much. At 2 A, the sweet spot (area of the LED in which the luminous flux is 20 % below the maximum possible luminous flux) is very close to the maximum current approved by the manufacturer.
The extremely high Vf, which is not to be expected with the modern LED chips used, is striking. The XHP35.2 LED chips are most likely also used for XHP50.3/70.3 and also XP-G2 new gen to XP-G4. In general, Cree seems to have massively reduced the selection of LED chips in order to achieve a high yield through mass production of fewer types and to reduce the unit costs enormously due to the extremely high number of units.
At 350 mA, each LED chip in a 4S circuit (4 in series) requires around 2.9 V. For comparison: the single LED chip of the XP-G4 requires a typical 2.92 V at 1000 mA, while one of the four LED chips of the XHP35.2 HI tested here requires a whopping 3.25 V at 1000 mA.
The comparison with the old XHP35 HI looks not so good.The XHP35 HI sample shown here was an LED in binning E2.As far as I know, this was never officially listed in the Cree data sheets and never appeared at generally known wholesalers (Mouser, RS, Digikey), but was available for a while via BLF/TLF users.
What also stands out:
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The max. luminous flux of the XHP35 is generally significantly higher.Although it is one step better binned, the almost 20 % difference in luminous flux is too high to explain the difference with this alone
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The Vf of the XHP35 is higher at the beginning until it falls below the voltage of the new XHP35.2 at around 1-1.2 A and remains well below this for the rest of the test.The difference at maximum current is over 600 mV!
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Due to the design with classic lateral chips and bonding wires, the Vf of the XHP35 continues to rise towards the end; the new version does not have this problem thanks to the flip chip design.
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The thermal resistance of the new version is not significantly lower than hoped for, as the maximum performance is more or less identical.
However, this could also simply be due to the (too) small footprint, despite the nominally better thermal resistance, because the heat dissipation surface is significantly smaller than with larger footprints such as 5050 or even 7070. But this remains speculation, especially as a Lumileds Luxeon MZ achieves over 60 W of power on a 3535 board.This implies that the maximum possible power in the 3535 footprint is likely to be somewhere between 55 and 65 W
Data for 25 °C Tsp (at 85 °C the luminance values are around 13 % lower).
Due to the sideways emitting chips (see die-shot at low operating current), the luminance is considerably lower than with the old XHP35, as the total illuminated area used increases significantly. Due to the lateral design of the XHP35 LED chips, they only radiate upwards.
This means that the XHP35.2 HI is no longer really usable for throwers. LEDs such as Luminus SFT-40 or -70 or Osram models such as CSLPM1.TG, which are operated at 3 V, should be preferred here. I see the XHP35.2 HI primarily as a sensible replacement for lamps with allrounder beam characteristics and the need for 12 V LEDs, especially as the maximum possible luminous flux should generally never be used in flashlights and the luminance is reduced even further as a result
The beam is fine, the minimal yellowish rings are not very disturbing - even when using SMO reflectors. There are no donut holes or other artifacts. Due to the side-emitting LED chips, the corona around the spot is more pronounced and merges evenly into the spill, a feature that is desirable for a usable all-round light pattern.
The tint is ok, although slightly greenish. With a duv of 0.0046, the color grouping is above the BBL but within ANSI limits. This LED is suitable for general use in mobile lighting technology. It should be noted here that there may be differences with regard to the tint, as the color group is relatively wide and also includes color tones above as well below BBL.
The CRI of 75 is above the minimum value specified by Cree. The R9 is low; nevertheless, it is well above the values of other LEDs with a 70 CRI rating. All in all, this LED is nevertheless a typical representative of the models with low color rendering - if this is desired, either the variants with high color rendering must be selected or other manufacturers such as Nichia must be used.
- Ra: 75
- R9: -22
- CCT: 5098 K
- duv: 0.0046
The XHP35.2 HI is quite a disappointment. Not only is the maximum performance barely higher than that of the old XHP35, the forward voltage is also significantly higher. In addition, the maximum achievable luminance is lower and the light pattern is generally less designed for throwers.
As experience has shown that the only real advantage of HI LEDs apart from their high luminance is their color stability over the entire beam angle, this is also the only sensible application, especially if an LED with 12 V forward voltage and the XP footprint is absolutely essential.
It seems that the XHP35.2 (HD / HI) was introduced primarily for cost reasons and to get rid of the more expensive first generation. There were no real improvements in luminance, optical properties or performance. The old XHP35 HI has set the bar so high that it will be difficult to significantly surpass it.
Pro
- Color stability over the entire beam angle
- Compatible with accessories for XP/3535 LEDs thanks to XP footprint
Neutral
- Only available in 12 V configuration
- Binning D4 not reached
Contra
- No increased performance
- Significantly reduced luminance
- Significantly higher Vf than the previous model
Thank you for reading the test. 