Feature

LED panels: backlit to the future

Integral has announced the introduction of a new backlit LED panel achieving 152lm/W output.

The LED panel has become the go-to fixture for general illumination in commercial spaces. Generally speaking, these LED luminaires provide a more comfortable ambience than some of the fluorescent horrors we’ve experienced over the last few decades. As a consequence, they’ve changed the way our commercial spaces look.

Two trends are being watched carefully. On the one hand, lumen output of the panels is driving ever higher. At the same time, the unit cost of panels is going the other way, with some panels being offered at embarrassingly low prices.

Let’s look at the cost first. We are all aware of ridiculously low prices on LED panels available on the internet. The guidance on buying any type of LED luminaire stands: a lighting supplier with a decent reputation to maintain will be able to provide full, certified, photometric performance data of its fixtures. Cheap lighting fixtures are cheap for a reason.

So where are we going with lumen output figures? While 200lm/W has long been a ‘grail’ number for the LED industry, we’re not there yet. Some would say that’s a good thing, but there is an argument in its favour, as discussed below. Meanwhile, the arrival of the 152lm/W LED light panel from Integral is to be welcomed, and it comes with an important development in LED panel technology.

Issues with edge-lighting

The first LED panels used edge-lighting. LED strips arranged around the inner face of the mounting frame of the fixture project light into the diffuser panel, which is then refracted downwards into the space. It’s an inefficient way to get light out of a fixture, but it’s a very cost-effective fixture to manufacture and transport. Further, having the LEDs within the depth of the frame means a very slim fixture, certainly slim enough to fit within the depth of plasterboard in a ceiling. And that can be a very attractive option for installers.

But it’s the technology within an edge-lit LED panel that has allowed prices to tumble. The unscrupulous panel manufacturer simply buys reels of cheap LED strip, mounts the strip into the frame and fits the diffuser. It’s this process that has made the LED panel market torturously competitive. Despite some fixtures coming without guarantees of build quality or performance, buyers are still very keen to purchase. The regret comes later.

Benefits of backlighting

Backlit LED panels are always more efficient than their edge-lit counterparts. Whereas the light created by the LED chips in an edge-lit fixture has to travel through the entire volume of the diffusing panel, the light from the matrix of LED chips in a backlit panel only travels through the thickness of the diffuser material – a matter of a few millimetres. Light losses within the fixture are lower, meaning a higher delivered lumen output.

If we can gain even higher efficiency from the LED chips themselves, then it makes sense to ensure that the overall luminaire is as efficient as it can be. This is what Integral has done with its 152lm/W backlit luminaire. With outputs of edge-lit LED panels at a respectable 113lm/W, we can imagine that improvements can be made. But it’s the backlit technology that’s making the running.

Integral is majoring on backlighting technology for its high-efficacy LED panels. Light values from the Integral LED low-profile backlit panels (600 x 600) show how this translates into excellent lighting performance: a 23W fixture provides output levels of 3500lm at 152lm/W. This is an important metric. When it comes to energy-saving initiatives such as The Carbon Trust, there is much to be gained when luminous efficacy figures reach this kind of level.

As an aside, it’s worth asking whether some of the early adopters of LED panels might benefit from scrapping their old edge-lit installations for this new generation of backlit panels, which offer such improved energy performance.

LED panels and health

The broader lighting community has been concerned about the drive towards higher light outputs from LED panels. How bright do we want our commercial interiors to be?

Good general lighting is a balancing act between available light and how that light is distributed within the interior space. There’s a rule of thumb that says, given average room metrics, a luminaire should provide 3000-4000lm into the space. Integral LED has sensibly contained its lumen output figures within a practical range that recognises the importance of uniform light distribution within a room.

But something is coming along that could well mean these potential high LED performances, including the long-sought 200lm/W, have a role to play. We have been asking what human-centric lighting (HCL) might mean in practical terms for some while; recent comments about the importance of circadian entrainment act as a signpost for high-output LED panels. Click here.

It could be that the most straightforward response to an HCL specification is to provide dimmable high-output LED panels capable of providing in excess of 1000lx, providing the conditions for circadian entrainment, which can then be dimmed to more typical illuminance levels.

Having access to high levels of illuminance can also be used in ‘daylight balancing’ schemes, where electric lighting is wanted to work alongside natural light coming into a space. We’ve never been able to adjust the artificial lighting component upwards before; this level of flexibility could herald a new approach to daylight planning.

But before everyone gets overexcited about the potential in this, let’s be clear. Human-centric lighting will demand first-class LED performance in terms of colour rendition. There will also be the question of colour temperatures and to what extent tunable whites will have a role to play. This is territory that can only be owned by luminaire manufacturers producing backlit LED panels of superior build quality. And that’s good news for everyone.