Imalent RT90 4800 lumen flashlight review

REVIEW – My friends will attest that I have a problem with flashlights, namely that I’ve never met a flashlight that I didn’t like (well at least until I’ve tried it out).  When the opportunity to review the Imalent RT90 4800 lumen flashlight came up, I jumped on the opportunity.  Let’s see if the RT90 lives up to its billing. (No that’s not a stubby-handled lightsaber up top)

What is it?

The Imalent RT90 is an IPX-8 (2 meter submergence) rechargeable LED flashlight with a rated output of 4800 lumens and a maximum beam throw of 1308 meters.  The RT90 is powered by four 10A, 3.6V 18500 lithium-ion (Li-ion) batteries that are recharged using a proprietary USB-A- to-magnetic adapter.

What’s in the box?

The RT90 arrived in a sharp-looking sleeved box that is secured with a magnetic closure.

Inside the box, the flashlight is nestled inside a custom cut foam liner. A second nook contains a small bag with two extra seals (for between the light head / switch / electronics and the battery assembly) and a charging cable in an imprinted box. A multi-language set of instructions was supposed to be included, but this was missing from my review sample.  Julie had to contact the manufacturer to get me an electronic copy since I could not find one on the website.

Hardware specs

The RT90 is cased in a hard-anodized aluminum alloy. The body and the o-rings give the flashlight an IPX-8 water resistance rating and a 1.5 meter impact rating.  The body is 128 mm long with a 65 mm head diameter and 51 mm body diameter. The flashlight weighs in a dense 435 grams. The business end of the flashlight has small crenelations around the top. These appear to be more for decorative or cooling than defensive purposes as they are not sharpened and are very short.

From the instruction sheet:

Design and features


To prepare the RT90 for use, the battery assembly must be unscrewed from the head and the isolation disc removed. The illustration and the as-implemented feature differ slightly (small green disc in the second image below versus the large disc in the first image).

Once the battery has been connected to the head assembly, the flashlight must be charged by connecting one end of the charging cable to a 2A USB port and the other end to the flashlight. The shapes of the flashlight housing and the magnetic charger reduce the chance of attaching the connector incorrectly.

The LEDs on the sides of the flashlight glow red during charging. The color changes to green when the battery pack is fully charged.


The RT90 is controlled by a single button located opposite the charging port.

A single press of the button actives the “normal” mode (default is Low setting). When the RT90 is in normal mode, depressing and holding the button cycles through “Low”, “Middle Low”, “Middle”, and “High” intensities. A second short press will turn the light back off. The RT90 will return to the last intensity used when normal mode is next activated. I am worried about the long-term durability and water resistance of the switch as it rattles and rotates when you manipulate it.

A double press when the light is off activates “Turbo” mode.

A double press from either Turbo or normal mode will activate the strobe feature.


To test the maximum throw distance, I shone the RT90 down the street that I live on.  The RT90 caused the driveway and road markers a quarter-mile down my street to return strong reflections (in addition to overwhelming the street-level illumination of the streetlamps).

To stress test the RT90, I ran the flashlight on Turbo mode for 30 minutes and measured the light output and temperature of both the light head and the battery assembly. I then let the flashlight cool back down to close to room temperature. I did not see a significant change in light intensity during my test.

As the graph shows, the RT90 will get uncomfortably hot during operation, but wearing a pair of heavy work gloves (leather or similar material) should keep you from getting burned.  The RT90 is supposed to have a thermal protection circuit that cuts the power output once the surface temperature of the flashlight reaches 122 degF (50 degC), but I did not notice any change in light output (could be an observer error, however). If the flashlight’s temperature crosses 150 degF (65 degC), the flashlight will lock out turbo mode until the flashlight has cooled.  These safety interlocks are supposed to protect both the LED and battery pack from thermal damage and reduce the risk of thermal runaway in the Li-ion batteries which can result in the cells rupturing / exploding / catching fire (this is a Li-ion battery chemistry issue, not something unique to the RT90).

To test how the flashlight works in the real world, I took the RT90 into my backyard and cycled through the different modes. Here’s a little video showing the different intensities and the strobe (my iPhone didn’t capture the strobe well due to the capture rate and strobe frequency interacting).

In short, the RT90’s turbo mode is good for short bursts (“Turbo is just for short bursts, Jason”) because of the rapid heating of the flashlight to uncomfortable levels, but the high setting puts out plenty of light for most extended uses.

Ongoing Maintenance

The o-ring between the battery assembly and the head should be cleaned and re-lubricated with silicone grease every 6 months.

What I like

  • Powerful light
  • Good water resistance rating
  • Compact package
  • No ports / port covers to worry about

What could to be improved

  • The switch needs to be improved so it feels less “janky”
  • I would prefer to see Qi-style charging system, in addition to / rather than the proprietary charger cable

Final thoughts

So far the RT90 has performed well, and I’m even starting to worry less about the switch.  It is too bulky for routine carry but makes an excellent garage / vehicle light.

Price: $149.95
Where to buy: Imalent Store and Amazon
Source: The sample of this product was provided by Imalent.

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