VLT and IRR Explained for Singapore Drivers
A plain-English breakdown of two numbers that matter on a window film spec sheet, VLT and IRR, and how to use them to compare films honestly.
TL;DR
- VLT (Visible Light Transmission) measures how much visible light passes through the film+glass; LTA requires ≥70% windscreen, ≥25% sides.
- IRR (Infrared Rejection) is the heat-band number that tracks how cool the cabin will feel, often quoted at peak wavelengths for marketing.
- Always ask for both peak and band-averaged IRR; peak figures alone overstate real-world heat performance.
- VLT is a legal constraint, not a heat-performance figure; a lighter film can reject far more heat than a darker one.
- For Singapore drivers, prioritise band-averaged IR rejection within the legal VLT envelope.
Window film spec sheets quote a lot of numbers. Most of them are noise. Two matter most: VLT and IRR. Understand these and you can compare films across brands honestly without falling for marketing.
VLT — what the law cares about
Visible Light Transmission is the percentage of visible light (380–780 nm wavelengths) that passes through the combined glass-plus-film. It's measured with a calibrated photometer, weighted by the human eye's sensitivity at each wavelength (the photopic response curve).
In Singapore, this is the metric the LTA regulates:
- Front windscreen: ≥70% combined VLT
- Side windows: ≥25%
- Rear windscreen: ≥25%
Singapore OEM windscreens typically measure 75–85% VLT before any aftermarket film. So the film needs to be around 88–92% VLT alone to keep the combined measurement comfortably above the legal 70%.
VLT does not tell you how much heat the film rejects. A film with VLT 70% can have either great or terrible heat performance, depending on chemistry.
IRR, what your cabin temperature cares about
Infrared Rejection measures how much of the infrared band (780–2500 nm) the film blocks. This is where most of the sun's heat lives in Singapore conditions, the near-infrared specifically (780–1500 nm). It is the spec that tracks most closely with how cool the cabin actually feels.
The trap with IRR is the wavelength window manufacturers choose:
- Peak IR rejection (often quoted): 95–99% at a specific peak wavelength like 950 nm. Sounds impressive.
- Band-averaged IR rejection (less commonly quoted): 60–80% across the full NIR band. Less impressive but more representative of real-world heat experience.
A film with "99% IR rejection at peak" might only reject 60% of total infrared. Always ask manufacturers for both numbers. The band-averaged figure is the honest one because the sun delivers heat across the whole NIR band, not just at one peak wavelength.
Typical band-averaged NIR rejection by chemistry:
- Dyed film: 20–40%
- Carbon film: 40–60%
- Ceramic film (nano-ceramic): 70–80%
- Premium multi-layer optical: 75–85%
How to actually compare films
Here's the practical decision framework when looking at spec sheets:
- Confirm VLT meets LTA rules (windscreen 70%, sides 25%). Anything else is non-starter.
- Compare band-averaged IRR at the same VLT level. A film with 80% band-averaged IR rejection at 70% VLT beats a film with 60% at 70% VLT, regardless of brand.
- Treat peak IRR with caution. Ask for peak AND band-averaged; the band-averaged figure predicts real-world heat performance, the peak figure flatters the spec sheet.
- Verify signal transparency. "Metal-free" or "ceramic" or "non-metallic" — Singapore vehicles with In-Vehicle Units need this confirmed.
- Check UV rejection. All quality films hit 99%. If a film quotes less, it's old chemistry.
A worked example
You're choosing between three films for the windscreen, all LTA-compliant:
| Film | VLT | IRR (peak) | IRR (band-averaged) | Metal-free? |
|---|---|---|---|---|
| A | 72% | 95% | 60% | Yes |
| B | 70% | 97% | 72% | Yes |
| C | 71% | 99% | 80% | Yes |
C wins on band-averaged IR rejection, the figure that tracks real heat performance, even though all three look similar on peak IRR at first glance.
Why VLT alone misleads
A common buyer mistake is choosing tint by darkness. "Darker = cooler" intuition is wrong for modern ceramic films.
A 70% VLT clear-IR film can reject the large majority of incoming near-infrared heat. A 30% VLT dyed film rejects far less of it. The clear film keeps the cabin cooler despite being "lighter."
This is why the LTA's 70% windscreen rule isn't the heat-performance limitation it sounds like. Modern spectrally selective films deliver excellent heat rejection at high VLT — the law and good thermal performance are compatible.
What about reflectivity?
A third spec sometimes appears: VLR (Visible Light Reflectance), the percentage of visible light bouncing off the film outward. High VLR creates a mirror appearance, which the LTA prohibits.
For non-mirror compliance:
- Premium ceramic and clear-IR films: VLR 6–10% (looks like glass)
- Older metallised films: VLR 15–25% (visibly mirrored)
If a film looks "mirror-like" from outside, it's either metallised (avoid) or going to fail VICOM. Premium nano-ceramic stays optically neutral.
Bottom line
For Singapore drivers asking us "which film should I get?":
- Confirm legal VLT (we measure your OEM glass first).
- Pick the film with the highest band-averaged IR rejection you can afford at that VLT.
- Confirm it's metal-free for ERP/GPS compatibility.
- Check the warranty covers the failure modes that matter (bubbling, peeling, silvering, fade, adhesive failure).
If you want help comparing specific products, WhatsApp Infratint with your vehicle and the film tier you're considering. We'll send you the relevant spec-sheet data and an honest comparison.