Many NHS ambulance specifications require V10 privacy glass, which allows approximately 10% visible light transmission. However, not all privacy glass is the same. This blog explains why V10 is specified, how it differs from standard privacy glass, and why choosing the correct glass matters.
When someone quotes for privacy glass, what exactly are they supplying?
It's a question that many ambulance builders and vehicle converters don't think to ask—until it's too late.
In many NHS ambulance projects, the specification calls for V10 privacy glass, which allows approximately 10% visible light transmission. This provides patient privacy while still allowing enough natural light into the vehicle for clinicians to work comfortably.
However, in our own independent testing, we've found that products described simply as privacy glass don't always achieve the same specification.
While they may look similar, they can perform very differently.
In this guide, we'll explain what V10 privacy glass is, why it matters for ambulance builders, and how you can check that the glass you're buying meets the specification you've been quoted.
V10 privacy glass is a specialist automotive glazing specification designed to provide approximately 10% visible light transmission (VLT).
In simple terms, around 10% of visible light passes through the glass.
This creates the high level of privacy expected within an ambulance while still allowing sufficient daylight into the patient compartment.
Getting this balance right is important.
Patients deserve dignity and privacy during transport and treatment, while clinicians need enough natural light to safely care for them.
That's why many NHS ambulance specifications require V10 privacy glass.
No.
This is one of the biggest misconceptions within the industry.
The phrase "privacy glass" simply describes tinted glass. It doesn't tell you how much light is actually passing through it.
During our own independent testing, we've found that some products marketed simply as privacy glass allow considerably more light through than genuine V10 glass.
In several cases, we've measured glazing that appears to have 20–25% visible light transmission rather than the approximately 10% expected from V10.
To the eye, the difference isn't always obvious.
But when you're manufacturing ambulances to meet a customer's specification, those differences matter.
There isn't necessarily one answer.
In our experience, there are two common reasons:
Some suppliers may simply be unaware of the exact specification required.
Others may supply a lighter privacy tint because darker V10 glass is more complex—and therefore more expensive—to manufacture.
That means two quotations for "privacy glass" may not actually be offering the same product.
If one quotation is significantly cheaper than another, it's worth asking exactly what specification of glass is being supplied.
A lower price isn't always comparing like-for-like.
Ambulance builders work hard to meet the specifications set out by NHS Ambulance Trusts.
If the glazing supplied doesn't match those requirements, it can create unnecessary problems later in the project.
Potential consequences include:
Having to replace glazing after inspection.
Additional labour and material costs.
Delays to vehicle delivery.
Questions around compliance with the original specification.
Reduced patient privacy compared with the intended design.
Simply asking the right questions before placing an order can help avoid these issues altogether.
At SGI, we don't simply describe our products as privacy glass.
We verify them.
Using a lux meter for glass transmittance, we're able to measure the amount of visible light passing through the glass and confirm whether it achieves the required specification.
Rather than relying on appearance alone, we use measured data.
This gives our customers confidence that the glazing they're fitting is exactly what they ordered.
We believe the easiest way to demonstrate quality is through transparency.
If you're unsure whether your current supplier's privacy glass is genuinely V10, we'll help you check.
The SGI V10 Challenge
Send us a sample of your existing glass.
Or arrange for us to visit your premises (location dependent).
We'll test the glass using our lux meter.
We'll share the measured results with you.
No obligation. No pressure. Just an independent assessment of the visible light transmission. We'd much rather help the industry understand the difference than simply ask people to take our word for it.
Since 1992, SGI has been manufacturing specialist vehicle glazing in the UK for ambulance builders, vehicle converters and specialist vehicle manufacturers.
Our ambulance glazing is trusted by many of the UK's leading conversion companies, including organisations such as WAS UK, O&H Vehicle Technology, Vehicle Conversion Specialists (VCS) and Wilker, among many others.
Every ambulance window is manufactured in-house in the UK and can be produced as:
Sliding ambulance windows
Bonded ambulance windows
Fixed privacy windows
Internal cab partition windows
Bespoke glazing solutions
All using high-quality glazing manufactured to ECE R43 (UN Regulation 43) safety standards.
If a quotation simply says "privacy glass," don't be afraid to ask a few more questions.
Ask:
Is this genuine V10 privacy glass?
What is the visible light transmission percentage?
How has it been tested?
Can you provide evidence of the specification?
Does it comply with ECE R43?
A supplier that can confidently answer those questions is far more likely to deliver glazing that matches your project's requirements.
Whether you're quoting for a new ambulance build, comparing suppliers or simply want to verify the glass you're currently using, the SGI team is happy to help.
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