Do solar control coatings change the colour of light?

A solar-control coating is a microscopically thin metallic layer, usually silver-based, baked onto one face of the glass inside a sealed double or triple unit. Its job is to reflect and absorb part of the sun’s near-infrared energy, the heat you cannot see, before it turns into warmth inside the room. That is what pulls the G-value down from around 0.6 for a clear unit to around 0.3 for a solar-control one.

The tint is a side effect of that metal layer. Reflecting a slice of the spectrum shifts the balance of the light that gets through, and the eye reads the result as a slight cool cast. It is the same physics as a pair of sunglasses, just a great deal weaker. A coating that stopped no visible light at all would look perfectly neutral, but it would also be doing less against glare, and the two things are linked. You are trading a small amount of colour neutrality for a large amount of heat control.

Coatings vary. Some are tuned to hold the colour as close to neutral as the chemistry allows, and the tint on those is genuinely hard to name. Others lean more openly blue or bronze. If colour matters to you, that is a question to put to the supplier directly, because two units with the same G-value can look slightly different against a white ceiling.

The honest answer is that most people stop noticing within a day. The human eye adjusts its own white balance constantly, the same way a room lit by a warm bulb stops looking orange after a few minutes. A faint cool cast on the daylight gets corrected out by your visual system almost as fast as it arrives.

Where it does read is in comparison. Stand in a room with one clear rooflight and one solar-control rooflight side by side and you will see the difference at once. Put the solar-control unit in on its own and there is nothing to compare it against, so it simply becomes what daylight looks like in that room. This is worth knowing if you are glazing two adjacent spaces, a kitchen and a hallway, say, because matching the glass across both will look more settled than mixing a clear unit with a coated one.

The other place it shows is on the outside. Looking up at a lantern from the garden, especially at a shallow angle, the coating can give the glass a slightly reflective, tinted appearance. On a flat roof you rarely see this from ground level. On a raised lantern that sits proud of a rear extension, you might. It is a look many people like, because it reads as considered rather than cheap, but it is fair to expect it.

There are two separate things people mean when they say a coating “changes the light”, and it helps to keep them apart. One is colour, the faint cast just described. The other is quantity, how much daylight comes through at all, and that is the bigger practical effect of the two.

Solar-control coatings cut visible light as well as heat. A clear double-glazed unit might let through 70 to 80 per cent of the daylight hitting it. A strong solar-control unit is often nearer 50 to 60 per cent. The room stays bright, because a rooflight collects sky from a wide angle and delivers a lot of light to begin with, but it is not as bright as it would be under clear glass. The figure to ask for is the light transmittance, sometimes written as LT or VLT, and you should read it alongside the G-value rather than on its own.

This is why orientation drives the whole decision. On a north-facing roof there is no strong sun to control, so paying in daylight and a touch of colour for a low G-value buys you very little, and clear glass is usually the better call. On a south-facing roof the sun is on the glass from mid-morning to late afternoon through the warm months, and the coating earns its keep. Getting that balance right for a given roof is the core of our energy-efficient skylight installation work: orientation first, then the glass specification, then the unit.

Southend-on-Sea faces south across the Thames Estuary, which is unusual for an English seaside city, and it changes the sums. A south-facing roof here has an open southern horizon with nothing in the way, so the glass collects sun from mid-morning until it swings west, with no neighbouring terrace or tree line to break it up. There is also reflected light off the water, which lifts the total on a bright day and is part of why estuary rooms can feel glary even when the sun is not straight on the glass.

On that kind of roof, the case for a solar-control coating is strong, and the faint tint is a small price for keeping a rear kitchen extension usable in July. The daylight loss is easily absorbed, because there is so much light arriving in the first place. The colour cast, against all that reflected brightness, is barely there. If anything, a slight cooling of very harsh estuary light can make a south-facing room more comfortable to sit in, not less. The overheating and glare are the real problem on these roofs, and a coating is the tool that addresses them, so this is one of the rare cases where the trade-offs almost all fall the right way.

Flat glazing is a special case worth flagging. A flat roof, a lantern or a walk-on rooflight points at the sky rather than at a compass direction, so it catches the high summer sun almost square on whichever way the house is turned. On those, a low G-value coating is nearly always worth having, and the colour question is secondary to the heat one. You can read the fuller reasoning on our flat roof skylight installation page.

Ask the supplier for a physical sample of the exact glass, not a description. “Solar control” is a phrase, not a colour, and the only way to know how a given coating looks is to hold it up to the sky. Look through it at a white surface and at the daylight, and look at it at an angle to see the reflected colour from outside. A sample the size of a beer mat tells you more than any spec sheet about the tint.

Then read the numbers alongside it. Ask for the G-value, the light transmittance and the U-value for the same build-up, so you can see what the colour and daylight are buying you in heat control. If the room already runs hot, a slightly stronger coating is usually worth the marginally deeper tint. If daylight is your priority and the roof does not face the sun, a lighter coating or clear glass may suit you better.

If you would rather we worked it out with you, tell us which way the roof faces and the rough opening size, and we will come back with a glass specification, the colour and daylight figures that go with it, and a price. Ring 01702 898232 or request a quote, and we will look at the whole roof rather than just the hole in it.