Date: 24th November, 2013
Pinball owners now have a choice when it comes to the type of playfield glass fitted to their machines. In the past few years anti-reflective glass has become a popular addition to home games, but which is the best at reducing reflections and glare, and which offers the best value for money?
There are three main options available for playfield glass. The simplest and cheapest is plain, tempered glass - the type supplied for decades and fitted as standard on most machines.
Then we have the anti-reflective type, which has a special coating on the surface of the glass to reduce the intensity and sharpness of reflections by scattering reflected light without distorting light passing through from the playfield side.
The two anti-reflective options commonly available are:
Other anti-reflective glass products have appeared from time to time but not in significant quantities, nor were they widely available. So we'll limit this review to considering the two main anti-reflective products above.
Plain, tempered glass is by far the cheapest option, adding nothing to the price of a game and only costing around £30 (€35, $35) a sheet to replace.
Invisiglass costs $295 + tax (€295 inc. VAT) a sheet, although it is occasionally available with a 'buy one, get one half price' deal at pinball shows in the US, bringing the price down to $220 per sheet when buying multiples of two.
Roman's/PDI glass costs $295 + tax (or €132 + VAT in Europe) for the regular size or for Safecracker, plus an additional €10 for a widebody sheet.
We haven't included shipping costs in the above prices, since the packaging requirements and delivery costs mean it is nearly always best to collect playfield glass in person.
Both anti-reflective glasses require careful cleaning to ensure you don't damage the coating. Pinball Decals sell a cleaning kit for their glass for $32.99, but the general advice with all anti-reflective glass advocates avoiding any harsh cleaning products such as those with ammonia, and use isopropyl alcohol either neat or mixed with distilled water.
Plain glass, of course, has no special cleaning requirements and is happy with just about any generic glass cleaning product.
So the downsides of anti-reflective glass are price and the need for careful handling. But what about the upsides? What do you get for your money, and which is best?
To find out, we did a couple of basic tests on the three types of glass. These tests were undertaken to see if and how the glasses alter the colour or intensity of the light passing through, and how they deal with strong sources of light reflection.
The first test to check for any colour tint placed a reference test chart under the glass and lit it from above, so the light had to pass through the glass twice. This was compared to the directly lit chart and any differences noted.
This test was carried out with natural overhead ambient light and the results standardised so the pure white of the test chart measured 230 our of 255 for all three colour channels to allow some headroom in case of reflections. The samples selected were representative of all the pixels in the indicated area. The intensity of any reflections were also noted, but not directly measured. In all cases the glass covers the bottom half of the picture.
We began with our reference, the plain glass.
The test showed a light loss of around 2.5%, or 1.25% in each direction which can be observed in the picture above. The glass also introduced a slight blue/green tint, although neither of these were considered significant. More of a problem was the strong reflection on the bottom left corner indicating the type of effect the anti-reflective glass sets out to reduce or eliminate.
Next we tested the Invisiglass.
The reflection was still present with the Invisiglass, although the intensity was diminished. The colour was much improved, with the scattering of the ambient light providing a slight lift with a marginal tendency towards a warmer red/yellow colour.
Finally we tested Roman's/PDI glass.
Colour-wise, the PDI glass has a very slight green/blue tint which was again not considered significant. More significant was way it handled the reflections, considerably reducing their intensity when compared to both the plain glass and Invisiglass.
Our second test and final test looked at how all three glasses coped with direct light source reflections - something the anti-reflective glasses are specifically designed to counter.
We took our trusty multi-LED torch and bounced its light off the surface of the glass to maximise the intensity of the reflection. We then normalised the images so the illumination of the test chart was consistent and compared the reflections.
Again, we begin with the reference plain glass.
The reflection is bright enough to burn out the image such that you cannot see the individual LEDs in the torch.
Next we have the Invisiglass.
Some of the structure of the LEDs can be seen, but the reflection is still quite intense and burns out the image sensor. It's interesting how the reflection is stronger above the LEDs than below, suggesting the anti-reflection effect is more effective at some angles than others.
Finally, here's Roman's/PDI glass.
The intensity of the reflection is much reduced and the arrangement of the LEDs becomes apparent for the first time.
Here are all three results from this test side-by-side.
When performing these test, we had no idea how the results would turn out. We knew from seeing it in action how both types of anti-reflective glass made appreciable differences, but we wanted to compare and - where possible - measure the effect.
Neither anti-reflective glass produced any noticeable colour cast or light reduction. By contrast, the plain glass was noticeably darker. Not hugely, but it was visible and measurable in the test.
Our impression going into these tests was that Invisiglass and Roman's/PDI glass were broadly comparable in their reflection-reducing capabilities. However, these results show how Roman's/PDI glass performed significantly better in these particular tests.
If plain glass offered 0% anti-reflectivity and Roman's/PDI Optical glass was 100%, we'd estimate Invisiglass sat around the 70% mark - a huge improvement, but not the best.
As for which of the three options offers the best value-for-money, that's more of a subjective judgment you have to make for yourself.
In the US, both anti-reflective glasses sell for the same price (discount offers excluded), so if you can get over the mental hurdle of paying $300 for a sheet of playfield glass, and all other things being equal, the PDI Optical glass has to be the way to go. When JJP are offering their 'buy one, get one half price' deal, the bang-for-the-buck from the two are more finely balanced.
In Europe, Invisiglass is considerably more expensive than Roman's glass (€295 v €132/€142 + VAT) making the decision easier and that hurdle a little less daunting.
For anyone with a top-end machine, the investment in anti-reflective glass is usually a worthwhile upgrade, providing an immediate and obvious improvement to the look of the game. As with adding a ColorDMD, the cost of the upgrade to anti-reflective glass can be partially recouped when selling, or a sheet of regular glass can be swapped in instead if the buyer doesn't want to pay the extra.
The only problem is; once you fit anti-reflective glass to one game you'll want to fit it to all of them. And that, depending on the size of your collection, can turn out to be really rather expensive.
All three products tested here came in the standard 3/16th (5mm) thickness, were made of tempered glass, and appeared to offer the same sound blocking capabilities.
The three glasses were tested in rapid succession to minimise variations due to ambient light differences.
All glasses reviewed here came from the same collection. The plain glass and Invisiglass sheets came pre-installed in new-in-box machines while the glass from Roman was purchased separately by the collection owner.
A review sample of Roman's/PDI glass was supplied for this test but not needed.
© Pinball News 2013