Glare on worktops, screens and islands

Heat gain is measured in watts arriving through the glass. Glare is measured in luminance, the brightness of a surface as your eye actually sees it, in candelas per square metre. The two do not track each other. You can take almost all the heat out of a pane with a solar-control coating and still be left with a sheet of glass showing a searing bright image of the sky, because that coating was never designed to dim the view. Cutting the energy and cutting the brightness are different jobs.

The eye copes with a huge span of absolute light levels, but it copes very badly with big differences of brightness sitting side by side in the same view. A clear midday sky reads at somewhere around 8,000 candelas per square metre, and the small disc of bright cloud next to the sun can be several times that. The pale worktop you are chopping on, lit to a comfortable working level, might be a few hundred. Put those two brightnesses in the same glance and the pupil closes down to protect itself against the bright one, and everything at the working level goes dark and hard to read. That mismatch is the whole of what glare is. Nothing about it depends on the room being warm.

This is why glare is worth treating as its own line on the specification. A quote can promise a low G-value, deliver on it, and still hand you a kitchen where the island top is unusable between the middle of the morning and the middle of the afternoon because it is mirroring the sky straight up into your eyes.

Three things make a surface a glare trap under a rooflight: it is horizontal, it is glossy, and it is where your attention is fixed. Worktops, islands and screens tick all three, which is why they are the surfaces people complain about rather than the walls or the floor.

Horizontal matters because a rooflight faces straight down at the surfaces below it. Light leaving the glass at a shallow angle strikes a level worktop and bounces straight back up towards standing eye height, so the geometry hands the reflection directly to the person working there. A wall gets the same light at a grazing angle and throws it somewhere else.

Gloss matters because of how the surface returns light. A matte finish scatters what lands on it in every direction, so the brightness is spread thin and no single point is painful. A polished or lacquered surface reflects like a weak mirror, keeping the light in a tight beam and preserving the image of whatever is above it. On a high-gloss island that image is the rooflight, reproduced at nearly its full brightness, sitting on the surface as a bright rectangle you cannot look past. The current fashion for handleless gloss kitchens and mirror-polished quartz has quietly made this worse in a lot of new extensions.

Screens are the sharpest case of all, because a screen is not only glossy, it is also the thing your eyes are locked onto for long stretches. A bright reflection laid over a monitor does not just annoy, it washes out the contrast of the text underneath it, so you lose the actual information. A glossy laptop lid under a south-facing loft rooflight can become genuinely unreadable, and no amount of turning up the screen brightness recovers it, because you are competing against the reflected sky.

Lighting engineers split glare into two types, and it helps to know which one you are fighting because the cure is different.

Disability glare is the one that stops you doing the task. A bright reflection sits on top of what you are trying to see and physically reduces the contrast, so the numbers on the hob dial, the recipe on the tablet or the text on the screen fade into it. The information is still there, but your eye can no longer separate it from the veil of reflected light laid over the top. On screens and documents this is called a veiling reflection, and it is measured by how far it drags down the contrast ratio of what you are reading.

Discomfort glare is the one that makes you want to leave. It does not necessarily stop you seeing, but the sheer brightness in your field of view is tiring and unpleasant, and it builds over minutes and hours rather than hitting all at once. A worktop returning a bright image of the sky produces both at once: it veils whatever is on the worktop and it wears you down.

The general rule lighting design works to is that the brightest thing in your normal field of view should not be more than about ten times brighter than the thing you are looking at, and ideally the task and its close surroundings sit within about three to one. A bare pane of clear glass showing an 8,000 candela sky over a worktop lit to perhaps 300 puts that ratio at more than twenty to one. You are miles outside the comfortable band, and the room tells you so within a few minutes of the sun coming round.

A wall window sits at the edge of your vision when you are facing into a room and working at a counter. You can turn your back to it, stand to one side of it, or shade it with a blind pulled down to eye level, and in every case the bright source is off to the side of where you are looking. A rooflight does none of that. It sits in the upper part of your field of view almost wherever you stand, and directly above the surfaces you work on.

That upward position is the problem. When you look down at a worktop or a screen, the rooflight is in the top of your view and its reflection is in the bottom, and the two brightness extremes bracket the exact spot your eye is trying to work. You cannot step out of it the way you can step out of a wall window’s beam. A run of flat-roof skylights over a kitchen, or a large roof lantern above an island, effectively fills the ceiling with sky, and every reflective surface underneath is going to show it.

There is a second effect that is easy to miss. A rooflight sees the whole dome of the sky, not just the patch a wall window frames, so it keeps feeding the room bright diffuse light even on an overcast day when there is no direct sun at all. A bright grey sky still reads at a couple of thousand candelas per square metre, which is more than enough to glare off a gloss surface. People assume glare is only a sunny-day issue and are surprised to find a mirror-finish worktop still hard to work on under flat cloud.

The glazing is the first lever, and it is a different lever from the one you pull for heat. For solar gain you want a low G-value with the daylight kept high. For glare you are working on the luminance of the pane and, more powerfully, on whether the glass shows a sharp image of the sky at all. Here are the common options and what each one does to brightness.

The important row is the diffusing glass. A solar-control coating lowers how bright the pane is but keeps it as a clear window, so a gloss worktop below still reflects a defined bright rectangle. Acid-etched or opal glass does something the coating cannot: it turns the pane from a window into a soft light source, spreading the sky into an even wash with no sharp edges and no mirror image to bounce off the surfaces below. The cost is the view. You give up seeing the clouds move, and you cannot combine full diffusion with a clear outlook in the same pane.

That trade decides where each belongs. Over a dining part of a room, where people look up and want the sky, clear or solar-control glass with the glare managed at the surface makes sense. Directly over a working island or a desk, where nobody is looking up and the reflection is the whole problem, a diffusing pane earns its place. On a mixed room it is common to specify different glass in different openings for exactly this reason, which is the same orientation-first thinking behind energy-efficient skylight installation: the glass is chosen for the plane and the room, not applied in one blanket specification across the roof.

You can also fix glare from below, by changing what the light lands on, and on a job where the kitchen is already being fitted this is often the cheaper and more effective move than reworking the roof. The finish of a worktop changes its glare behaviour far more than its colour does.

The pattern is the same every time. A matte finish scatters the light and spreads the brightness so thin that no point is uncomfortable, while a gloss finish keeps it concentrated and returns the image of the sky intact. Choosing a honed rather than a polished worktop, at the point when the kitchen is being ordered, removes most of the problem for no extra cost, and it does it without touching the glazing at all. The same is true of screens: an anti-glare panel or a matte screen protector fixes a workstation that a glossy one makes unusable.

Where the opening goes changes how much glare reaches the surfaces, and this is decided long before anyone orders glass, at the point of setting out the roof. Two openings of the same size and the same glass will behave very differently depending on what sits under them.

• Keep the rooflight off the direct line above the busiest reflective surface where you can. A skylight set over the walkway or the dining zone, rather than plumb over the island, lights the room without putting its image on the work surface.
• Face the working side of an island north where the layout allows it, so the person standing at it has their back to the brightest part of the sky rather than facing into its reflection.
• For a home office in a loft, set the desk so the screen is edge-on to the rooflight rather than square under it. A screen at ninety degrees to the bright source catches far less veiling reflection than one facing it.
• Fit blinds you will actually use. Integral blinds inside the glass unit, or electrically operated ones on out-of-reach openings, get used because they take a button rather than a pole. A blind that needs a stepladder gets left up. Electric operation earns its keep here, which is part of why electric opening units suit high ceilings.
• Remember that a light-coloured ceiling and pale walls around the opening reduce the contrast between the bright pane and its surroundings, which softens discomfort glare even when the pane itself stays bright.

None of these needs any special glazing. They are about the geometry of where the bright source sits relative to where you look, and they cost nothing if they are thought about while the roof and the kitchen are still on paper. The trouble is that the rooflight and the kitchen are usually designed by different people who never compare notes, so the island lands directly under the lantern by accident.

South Essex has an enormous stock of 1930s semis, and the standard move on them is a rear extension across the back with a kitchen and dining space knocked through into one, glazed overhead to bring light into the deep plan. With a south-facing garden, which a great many of these have, the rooflight over that extension is pointed straight at the brightest part of the sky for the whole working day. Southend-on-Sea faces south across the Thames Estuary, and the estuary is a large flat reflective surface throwing yet more diffuse light up onto every south-facing roof plane along the coast, so the sky those rooflights see is brighter here than it would be inland.

Drop a gloss handleless kitchen with a polished island into a room like that and you have assembled every ingredient of a glare problem: a south rooflight, an open horizon, extra reflected light off the water, and a mirror-finish surface waiting underneath to bounce it into your eyes. The loft conversions in the Victorian and Edwardian terraces along the cliff have the office version of the same problem, a screen under a south-facing slope with nothing shading it.

The fix is the thing this business is built on: specify for the aspect before you buy the unit. Work out which way the plane faces, decide whether that opening wants clear glass, solar-control glass or a diffusing pane, set it clear of the surface it would otherwise glare off, and match the worktop finish to suit. Glare, solar gain and the low winter sun are all the same south-facing question asked three ways, and a survey answers all three at once. If you want that worked out for your own roof and your own layout before anything is ordered, ask us for a specification that covers the glare as well as the heat, plane by plane.