As its name suggests, the HD91+ is an improved version of 2014’s HD91 projector. It keeps the key LED DLP lighting system that made the HD91 so unique for the sub-£5,000 projection market, but delivers enhancements to its predecessor’s brightness and contrast. But do the changes do enough to elevate the HD91+ from the HD91’s "good" level to excellent?
The HD91+ looks identical to the HD91. This is no bad thing: Its elongated shape, liberal use of angles, curved bodywork and large, centrally mounted lens make it more attractive than most projectors on the market. It even manages to inject a dash of colour in the form of a red ring around the lens.
It’s promising to note, too, that the bodywork incorporates what appear to be large venting "wings". Experience suggests these will prove helpful in keeping a lid on the projector’s running noise.
See also: Best projectors 2015
Connectivity is fairly strong. The two HDMIs are built to the HDMI 1.4 spec; this is a Full HD projector rather than a UHD one. There are two 12V trigger outputs for driving, say, motorised screens and curtains, plus a component video input.
You'll also find a RS-232 for integrating the projector into a wider home-entertainment system, a USB port for applying potential firmware updates, and a jack for attaching an optional extra 3D transmitter.
The HD91+’s unique selling point is its DLP LED lighting system. While normal UHP projection lamps tend to last between 2,000 and 4,000 hours, the LED lighting in the HD91 Plus is rated at a mammoth 20,000 hours. That’s long enough to watch 10,000 two-hour films, and effectively means that you’ll never need to change the bulb throughout the projector’s working life.
This isn't the only benefit of LED lighting. It should also enable you to continue watching the HD91+ for every one of those 20,000 hours with a minimal loss in picture quality. Traditional lamps, by comparison, lose brightness and colour response quite dramatically in the course of their operating lives.
LED lamps should also deliver more stable colours than normal lamps. In addition, since they’re much easier to keep cool than normal lamps, turning the HD91+ on and off is pretty much an instant affair, with no warm up/warm down process required. The relative heat efficiency of LED lighting should also help it run more quietly than rivals.
The HD91+ boasts a light output of 1,300 lumens and a contrast ratio of 600,000:1, versus the 1,000 lumens and 500,000:1 of the original HD91. These represent surprisingly large on-paper improvements for a projector that adds only a "+" sign to the name of its predecessor, and they immediately raise hopes of a significant performance boost.
The final noteworthy features of the HD91+ is its PureEngine video-processing engine, which includes tools for enhancing motion, colour and sharpness. It also offers a huge suite of picture setup tools that mean the projector is able to support a professional installation by a trained Imaging Science Foundation (ISF) calibrator.
The original HD91 was a tricky beast from which to get the best; I certainly struggled to find an out-of-the-box setting that I liked. Fortunately, perhaps because of its brightness and contrast improvements, the HD91+ delivers far better instant results – although the comprehensive nature of its adjustments is nonetheless welcome.
For many users the Cinema or, more likely, Film picture presets will be the best starting point, although there’s also a Reference mode that turns off all the projector’s processing for AV fans wanting the "purest" experience.
Personally, I was surprised to find that I quite liked using the PureEngine system. I generally left Ultra Resolution on and both PureMotion and PureColour on their lowest power setting. The only exception to this was gaming, where you need to turn off as much processing as possible to try to minimise the amount of time it takes the HD91+ to render its images.
I also found it was necessary to use the colour-management tools to reduce a slight infusion of reddish-pink that creeps into very dark scenes. However, by far the most important setting to learn your way round is the Dynamic Black feature.
This adjusts the picture’s luminance continuously based an an analysis of the picture being shown – but, for reasons I’ll get into in the Picture Quality section, I found the Dynamic Black 2 and 3 settings pretty much unusable. As a result, I’d suggest using the Dynamic Black 1 setting, since turning the feature off entirely reduces the projector’s contrast performance to a point where it doesn’t quite hit the spot for a projector costing £3,500.
If you find even Dynamic Black 1 uncomfortable, then I’d suggest using the non-dynamic LED Brightness feature set to around 60% for a dark room or around 70-75% if there’s some ambient light with which to compete.
When it comes to the physical side of setting up, the HD91 Plus is pleasingly flexible. It sports a 1.9x optical zoom – more than you customarily get with DLP projectors – and there are simple wheel adjustments for optically shifting the image horizontally or vertically. This means you shouldn’t have to distort the image with digital keystone correction.
Zoom and focus are achieved via simple, reasonably taut rings around the lens. However, the thought did occur to me that a motorised system might have been nice on a £3,500 projector.