Does solar control glass make a room darker?

Sunlight carries visible light, infrared heat and ultraviolet. A solar control coating is aimed at the last two, and it is built so that the first passes through with as little loss as the chemistry allows.

The coating is a stack of very thin metal and oxide layers, laid on one face of one pane inside the sealed unit. Each layer is a fraction of the width of a hair. Together they reflect a good share of the infrared, the part of the spectrum you feel as warmth, and they let most of the visible band go straight through. To the eye the glass looks clear, or very slightly green or blue when you see it edge-on or against a white wall.

Some light is always lost. Every pane of glass in the path costs a little, and a coating costs a little more. So yes, a coated unit is fractionally dimmer than an uncoated one. You will not notice that in a loft bedroom or a kitchen lantern on a normal day. You might notice it on a dull November afternoon if you switch between two samples, which is why we like to hold them up at the survey.

Our page on solar control glass for rooflights explains how the coating is built. This page stays with the brightness question.

Every reputable glass data sheet gives a light transmittance and a g-value. Read them as a pair, because a good unit has a high first number and a low second one.

Light transmittance is the share of visible light that gets through the whole unit. The g-value is the share of the sun's energy that gets through, heat included. A plain double glazed unit has a high figure for both. A solar control unit keeps the first high and brings the second down. A dark or mirrored unit brings both down together, which cools the room and darkens it.

Ask for both numbers from the same data sheet, for the whole unit and not a single pane. If a quote gives you only the g-value, the brightness half of the story is missing. Our answers on light transmittance on a rooflight and on the g-value of rooflight glass take each number on its own.

When a room does go darker after a glazing change, the cause is usually a tint, not the coating. The two are different things and are often confused.

A tinted pane is coloured through its thickness. It absorbs part of the light as well as the heat, and the absorbed energy warms the glass itself. Grey and bronze are the usual choices. They cut glare and they cut brightness in the same stroke. Put a tinted pane over a north-facing bedroom and the room will feel dim, because there was never much direct sun to tame in the first place.

A coated pane does the work on the inside surface and leaves the body of the glass clear. It is the better fit for a room that needs light first and heat control second, which describes a typical loft room or extension in Crawley and the towns around it.

Two other things change how bright a room looks, and neither is the glass:

• Dirt and shading. A rooflight with a film of pollen or a neighbour's overhanging tree will lose more light than a coating ever does.
• Room finishes. White reveals and a pale ceiling bounce daylight deeper into the room. Dark plaster around the opening swallows it.

The benefit depends on which way the glass faces and how the room is used. The brightness cost is small either way, so the question is whether the heat control pays you back.

A south or west facing rooflight over a home office takes strong sun in the afternoon. The coating keeps the desk comfortable and cuts the glare on a screen, and the room stays light. Over a kitchen lantern with a south-facing slope, the same logic applies. On a north-facing roof window, the gain is small, and a higher-transmittance unit may suit better. Our page on choosing energy efficient rooflights by orientation goes through each aspect, and the one on stopping a rooflight room from overheating covers the summer case.

The coating also sits comfortably with the rest of the build. A unit can carry a low-E layer for winter warmth, a solar control layer for summer, and a laminated acoustic inner pane for quiet, all in one sealed double unit. We write the chosen combination into the quiet spec that comes with every quote, so you can see the glass named before anything is ordered.

Will a coated rooflight look tinted from outside?

A neutral solar control unit shows a faint cast in some lights, usually green or blue. It is far subtler than a tint, and from the street a passer-by reads it as ordinary clear glass catching the sky.

Can I add a coating to my existing rooflight?

The coating is applied to the glass inside a factory-sealed unit, so it cannot be added afterwards in any lasting way. The route is a new sealed unit or a new rooflight. Our page on upgrading an old rooflight explains the options.

Is self-cleaning glass the same as solar control glass?

No. Self-cleaning glass has a separate outer coating that helps rain wash off dirt. It can be combined with a solar control layer inside the unit, and the two do not interfere.

Does solar control glass affect how much noise gets in?

The coating itself does not. The pane thickness and the laminated interlayer are what change the sound, so the two choices can be made separately. See one glazing build for warmth and quiet.

If you want a bright room that stays comfortable in July, get a quote and we will specify the coating against the light your roof actually gets. The wider service sits on our energy efficient rooflights hub.