A spec sheet looks like a fact. It has a number, a unit, sometimes a test method in parentheses. What it doesn’t say — on most sheets, in most places — is the one detail that decides whether that number applies to your window at all: the glass it was measured on. This post walks through VLT, SHGC, TSER, IR rejection, glare and UV, sourced directly to the manufacturer and standards-body documents that define them, so a buyer can ask sharper questions of any quote.
Published September 10, 2026 · Armored Glass Solutions
The Reference-Glass Trap
Start with the fact that carries the most weight in this whole subject, because it comes straight from manufacturer spec sheets rather than a secondary summary of them. 3M’s own CSI-format technical data sheet for its Prestige Series film states, in a footnote most readers skip: “Note: Performances are based upon 1/4” (6.4 mm) clear glass.” LLumar’s published performance-definitions page carries its own version of the same disclosure, for a different reference thickness: “Remember that this number is measured for a film on clear, 3mm glass, unless otherwise stated.”
Sit with what that means. Two major manufacturers, publishing figures for the same category of product, each tied to a different piece of reference glass — a quarter-inch clear pane in one case, 3 millimeters of clear glass in the other. Neither number was measured on your window. If your glazing is tinted, tempered, laminated, coated with a Low-E layer, or part of a double- or triple-pane insulated unit, the film’s real-world SHGC, TSER and VLT on that assembly will differ from what’s printed on the sheet — sometimes by a little, sometimes by a lot, depending how far your glass is from the manufacturer’s reference substrate.
The window film industry’s own standards body has said this plainly, in a technical paper adopted by its full technical committee: “window film manufacturers measure performance with film applied to glass, while many distributors and installers measure performance of the window film alone. This can lead to significant differences between manufacturer values… and measurements with handheld devices.” That’s the European Window Film Association (EWFA, the European chapter of the IWFA), describing a gap that exists between lab-published numbers, field measurements, and the glass actually sitting in your frame — three different things that don’t automatically agree.
None of this means the published numbers are wrong. It means they’re answers to a specific, stated question — “what does this film do on this reference glass” — and the honest next question is whether your glass is close enough to that reference for the number to still apply. A spec sheet that names its reference glass, like 3M’s and LLumar’s do, is giving you the information you need to ask that question. One that doesn’t name it is asking you to trust a number without the substrate it was built on.
Whose Number Is It, Really
LLumar defines Solar Heat Gain Coefficient as “the fraction of incident solar radiation that actually passes through that window, including solar energy that is both directly transmitted and that which is absorbed and subsequently released inwardly by re-radiation and conduction.” It’s a 0-to-1 figure: an SHGC of 0.30 means roughly 30 percent of available solar heat gain makes it through. Read the definition again and notice what it’s measuring — “that window,” the whole assembly, not a sheet of film held up in isolation.
That’s not incidental phrasing. NFRC 200, the standard governing SHGC and visible-transmittance ratings, is scoped to fenestration products “containing glazings or glazing with applied films” — film-on-glass, as an assembly, is what gets rated. The European equivalent makes the same point from a different standards body: EWFA’s technical paper describes the g-value (SHGC’s European counterpart) as “a weighted calculation across the entire solar spectrum from 300 to 2,500 nm… The North American equivalent is the Solar Heat Gain Coefficient, SHGC. This value is the amount of solar radiation transmitted through a window, door, or skylight, and absorbed and subsequently released as heat inside a building or vehicle.” Window, door, or skylight — not film.
Avery Dennison’s own architectural glossary is consistent with both, defining Total Solar Energy Rejected as “the percentage of total solar energy rejected/screened out by a glazing system” — the phrase “glazing system” appears throughout the manufacturer’s own definitions, not as marketing softening, but because that’s literally what the number measures. A film on 6mm clear glass and the same film on a tinted double-pane unit are two different glazing systems, even though the film itself hasn’t changed. The number belongs to the system, not the sheet of film sold separately from it.
TSER, Decoded
Total Solar Energy Rejected shows up on almost every film brochure, usually as the headline number. LLumar defines it as “the percent of incident solar energy rejected by a glazing system. This value equals solar reflectance plus the part of solar absorption that is both re-radiated and conducted/convected outwardly.” Avery Dennison’s version adds a practical note: “The higher the TSER number, the more solar energy is rejected, and the more effective the window is in screening solar radiation.”
Here’s the part that’s easy to miss: TSER and SHGC aren’t two independent measurements of a film. They’re close to the same measurement, expressed two different ways. EWFA states it directly: TSER “is calculated directly from the g-value/solar factor” — meaning TSER is derived from SHGC rather than measured separately, roughly TSER% equals (1 minus SHGC) times 100. A film reporting a 0.30 SHGC and a film reporting a 70 percent TSER are, broadly, describing the same performance from opposite ends.
Worth knowing before a quote leans on the term: TSER is not an NFRC-certified rating category the way SHGC and visible transmittance are. NFRC’s certified labels report SHGC and VT. TSER is the window film industry’s own derived figure, defined and promoted by IWFA and EWFA and calculated from standards-based inputs — 3M’s own Prestige spec sheet cites ASTM E903 (the standard for solar absorptance, reflectance and transmittance of glass materials) next to its published figures. That doesn’t make TSER meaningless. It means a TSER number is an industry convention communicating the same underlying physics as SHGC, not a separate independently-verified rating sitting alongside it.
The IR-Rejection Marketing Problem
This is the most direct admission in any of the sourcing behind this post, and it comes from the industry’s own technical committee, not a critic of it. EWFA’s technical paper on infrared energy rejection states: “Infrared Energy Rejection, IRER: IRER is a measurement of infrared rejection over the IR range of 780–2,500 nanometres… The IWFA has defined IRER in response to non-standard publication of solar IR rejection specifications in the window film industry.” A standards body created a new, precisely-scoped metric because “IR rejection” as a phrase was being published without a consistent range behind it.
The paper draws a clean distinction between IRER and a narrower cousin: “Selective IR Rejection, SIRR: SIRR is a measurement over a selected wavelength range (e.g. 900–1,000 nanometres) or possibly at a specific wavelength (e.g. 910 nm). SIRR is similar to IRER, however it does not take into consideration the reradiated absorbed energy, but only the directly transmitted energy.” A number measured over a 100-nanometer slice of the spectrum, or at a single wavelength, is a real number — it just isn’t answering the same question as a figure measured across the full 780-to-2,500nm infrared range.
Field measurement adds a third layer. EWFA notes that handheld devices commonly used on job sites “generally measure infrared radiation over a limited 800–1,400 nm range or at a specific wavelength (e.g. 940 nm only)… it may not show the same value as laboratory measurements that are conducted over the full infrared range.” A meter reading on-site, a narrow-band spec on a brochure, and a full-range lab figure can all be describing the same film and land on visibly different numbers. EWFA’s own recommendation is to standardize on the full range: it “recommend[s] providing the infrared measured data for the full radiation range (780–2,500 nm) and display[ing] this data as such on the product’s data sheets.” That’s the question worth asking any quote citing an IR-rejection figure: full range, or a narrow band?
VLT, U-Factor and Emissivity
Visible Light Transmittance is the most intuitive figure on a spec sheet, and manufacturers define it consistently. LLumar: “the ratio of the amount of total visible solar energy (380-780 nanometers) that is allowed to pass through a glazing system to the amount of total visible solar energy falling on the glazing system.” EWFA corroborates the wavelength range: “A typical human eye can see from 380 to 780 nm.” Like SHGC and TSER, VLT is measured against a glazing system using UV-VIS-NIR spectrophotometers with an integrating sphere — instruments EWFA describes as “capable of measuring the electromagnetic radiation that is transmitted and reflected at each wavelength across the solar spectrum (300 to 2,500 nm) through a window film and glass.”
U-factor and emissivity are a different family of metric entirely, and worth not confusing with solar heat gain numbers. LLumar defines U-value as “the overall heat transfer coefficient of the glazing system… a measure of the heat transfer that occurs through the glazing system between its outer and inner surfaces.” Avery Dennison’s glossary adds that it’s “given as center-of-glass value in winter conditions. The lower the U-value, the better the insulation qualities of the glazing system.” Emissivity, per the same glossary, is “a measurement of a surface’s ability to absorb or reflect radiant energy… the lower the emissivity rating, the better the insulation characteristics.” These describe how well the assembly holds heat in or out — a winter, whole-building-envelope question — not how much solar heat gets through on a hot afternoon, which is what SHGC and TSER measure. A film’s marketing can lead with a strong TSER while saying nothing about U-factor at all, and that’s not a contradiction; they’re different questions. NFRC 200’s underlying SHGC and VT calculations are run through the WINDOW and THERM modeling tools developed at Lawrence Berkeley National Laboratory — the same federal lab whose optical-data database, described below, underpins NFRC’s film certification pathway.
Glare and UV — the Two Numbers Everyone Gets Right
Glare reduction is defined by Avery Dennison plainly: “Glare usually is defined as being the difficulty of seeing in the presence of a bright light. A high glare reduction is usually achieved with a darker film.” The same glossary offers concrete guidance on how dark is dark enough: “In order to achieve effective protection against glare from sunlight, a comparatively dark film type should be selected. Here we recommend a visible light transmission of no more than 20%, otherwise perceived brightness is not reduced sufficiently.” The practical read: a glare figure is meaningful relative to the VLT of your existing, unfilmed glass, not as a stand-alone absolute claim — a film that reduces glare noticeably on clear single-pane glass may do far less on glass that’s already tinted.
UV rejection is the one figure on most spec sheets that’s remarkably consistent, and that consistency is itself the point. EWFA describes films generally as “preventing more than 99% of harmful UV radiation from entering a building or vehicle.” Avery Dennison publishes the identical figure across two different product tiers in its own catalog: its UV-protection line “filters out more than 99% of harmful UV rays,” and separately, its safety and anti-graffiti films “protect against 99% of all UV radiation.” Same number, different product families, same manufacturer. Because UV wavelengths sit at the low-energy edge of the solar spectrum, most films on the market — including basic, lower-cost dyed films — block close to all of it. That makes ~99% UV rejection close to a baseline for the category rather than a distinguishing feature worth choosing a product on.
NFRC and Window Film
Window film does have a real NFRC certification pathway, documented directly in NFRC’s own fact sheet on the program: a manufacturer “submit[s] their film’s optical properties for acceptance in the [database] hosted by Lawrence Berkeley National Labs at [the] Verification Program for Optical Spectral Data (NFRC 302).” From there, “the manufacturer contacts and chooses an NFRC-accredited simulation laboratory. The laboratory determines the product’s energy performance ratings by using the optical [data]” and finally “selects an NFRC licensed Certification and Inspection Agency… to conduct an in-plant [inspection]. Once the IA has determined that all certification requirements [are met]… the manufacturer may now place these approved performance rating values” on packaging and labels.
NFRC’s own consumer-facing page confirms the program is real and points buyers toward it: “NFRC independently tests, certifies, and labels window films for their energy efficiency… If you make the decision to purchase window film, be sure to look for the NFRC label on the product packaging.” What that page doesn’t spell out, and what’s worth understanding before treating any NFRC-adjacent claim as universal: the certification runs through the same film-plus-glass logic as everything else in this post. It certifies a specific film applied to a specific, documented glazing — not “this film” as an abstract, context-free number that applies to whatever glass it eventually gets installed on.
What to Ask
None of this is a case against any manufacturer — 3M, LLumar and Avery Dennison all publish the definitions and reference-glass disclosures cited throughout this post, which is more transparency than the industry is sometimes given credit for. The gap isn’t that the numbers are hidden; it’s that a brochure headline rarely repeats the fine print next to it. A handful of questions close that gap on any quote, for any brand:
What glass was this SHGC or TSER number measured on? A quarter-inch clear reference pane and your actual tinted, tempered or insulated glazing are not the same substrate, and the film’s real performance on your glass will shift accordingly.
Is the IR-rejection figure full-range (IRER, 780–2,500nm) or a narrower measurement (SIRR)? Both are legitimate numbers; they answer different questions, and a sheet that doesn’t say which one it’s reporting is worth a follow-up call.
Is this figure NFRC-certified, or a manufacturer-published lab result? Both can be accurate. An NFRC listing has been through an accredited lab and an inspection agency; a manufacturer figure is the company’s own published data. Knowing which one you’re looking at is reasonable due diligence, not skepticism for its own sake.
Is a comparison between two films actually apples-to-apples? If one sheet reports TSER on 3mm reference glass and another reports SHGC on 6.4mm reference glass, converting one to the other and lining them up against the same reference point is the only way to compare them fairly.
How We Work
A call in usually gets a callback the same business day. We schedule a free in-person site assessment anywhere in LA or Orange County, where we look at the actual glass — type, thickness, coatings, pane configuration — rather than pricing from a description alone. The written spec that follows names the product, cites the manufacturer’s data sheet, and is built around your glazing, not a reference substrate on a brochure. From there it’s your call: keep it, shop it, or book us.
Questions
No, not directly. Each manufacturer number is measured against a stated reference glass. 3M’s own Prestige spec sheet notes that its figures are “based upon 1/4” (6.4 mm) clear glass,” while LLumar’s definitions page says its numbers are measured “for a film on clear, 3mm glass, unless otherwise stated.” Two different manufacturers, two different reference substrates. Your actual glass is likely tinted, tempered, laminated, Low-E coated, or part of a double-pane unit, and that changes what the same film actually delivers.
They describe the same underlying heat performance from two different angles. The EWFA technical paper states TSER “is calculated directly from the g-value/solar factor,” the European equivalent of SHGC, so TSER is roughly 1 minus SHGC, expressed as a percentage. SHGC is the metric NFRC certifies on a fenestration label. TSER is the window film industry’s own derived term, defined and promoted by IWFA/EWFA, not an NFRC-certified rating category in its own right.
Yes, through a specific technical pathway: a manufacturer submits optical data under NFRC 302 to a database hosted by Lawrence Berkeley National Laboratory, an NFRC-accredited simulation lab calculates the energy performance ratings from that data, and a licensed inspection agency audits the manufacturing plant before the ratings can appear on packaging. But a listing certifies a specific film applied to a specific glass, not the film as a stand-alone, universal number.
It depends what range was measured. EWFA distinguishes full-range Infrared Energy Rejection (IRER, measured 780 to 2,500 nanometers) from Selective IR Rejection (SIRR, measured over a narrow band or a single wavelength like 910 nm). EWFA states plainly that IWFA “defined IRER in response to non-standard publication of solar IR rejection specifications in the window film industry” — a standards body creating a new metric specifically because narrow-band numbers were being published without saying so.
Keep Reading
The reflectance numbers this post skips: exterior vs. interior, and why they predict what a mirror film does after dark.
Read the post →VLT, heat rejection and glare explained in plain terms, and when a lower-cost film is genuinely the right call.
Read the post →What a real visit measures, tests, and asks before any product gets named.
Read the post →Free in-person site assessment anywhere in LA or Orange County. We look at your glazing directly and send a written spec citing the manufacturer’s own data — no obligation.