How to Read a Blue Light Lens Transmission Chart

Melavue Midnight red lens and DayLight yellow lens glasses beside a notebook with a hand-drawn light curve on a cream desk

Short answer: A transmission chart shows how much light gets through a lens at each color (wavelength). Left to right is wavelength in nanometers (nm), from violet and blue to green, yellow and red. Bottom to top is the percentage that gets through. The lower the line, the more the lens blocks. For sleep, the part to check runs from blue into green, roughly 455 to 560 nm, the range researchers call "circadian-proficient" (Mason et al., 2022). A single "blocks X% of blue light" number can't tell you that. A full chart, from a named lab, for the exact lens you're buying, can.

What is a lens transmission chart?

It's a graph made with a spectrophotometer, a machine that shines light through a lens and measures what comes out at each wavelength. Researchers use the same method to compare lenses (Mason et al., 2022; Leung et al., 2017). Some brands publish one; many publish only a percentage.

How to read it in four steps

Find the axes. The bottom (x-axis) is wavelength in nm, usually about 280–780. Below 400 is ultraviolet (UV), roughly 400–500 is violet and blue, 500–570 is green, and above that is yellow, orange and red. The side (y-axis) is "% transmittance": 100% means all the light gets through, 0% means none does.
Look at 450–500 nm. The light sensor that sets your body clock (melanopsin) is most sensitive around 480 nm (Brown et al., 2022; Lucas et al., 2014). For an evening lens, you want the line low here.
Keep going into green, to about 560 nm. Researchers who tested 50 lenses counted 455–560 nm as the body-clock range (Mason et al., 2022). A lens that blocks blue but lets green straight through does only part of the evening job.
Find where the line climbs. Every tinted lens lets light through somewhere, or you couldn't see. The point where the curve shoots up tells you the lens's character: deep red lenses climb late, in the orange-red; yellow lenses climb early, in the blue-green.

How to read a lens transmission chart: wavelength along the bottom from violet to red, percent of light let through up the side, with the blue-to-green body-clock range highlighted

What different lens colors look like on a chart

Lens type	What the curve usually looks like	Best for
Clear "blue light" lens	High almost everywhere, with a small dip in the blue	Little effect on body-clock light
Yellow	Low at the far violet-blue end, rising early	Daytime screens, as a comfort choice
Orange / amber	Low through blue, rising in the green-yellow	Evenings
Red	Low through blue and green, rising late	The last hours before bed
Grey sunglass tint	Low and fairly flat across all colors	Bright sun, not specifically blue

What the research found when it measured real lenses:

Clear lenses barely touch body-clock light. Clear lenses with a blue reflective coating let through 76.5% to 92.2% of circadian-proficient light (Mason et al., 2022). Another study calculated that five blue-light filtering lenses sold for everyday wear cut melatonin suppression by only 5.8% to 15% (Leung et al., 2017).
Red and orange block the most. Red lenses let through 0.62% to 17.22% of that light, and orange 2.9% to 28.2% (Mason et al., 2022).
Yellow, pink and brown vary widely, so read the chart, not the color (Mason et al., 2022).

Why "blocks 99% of blue light" isn't enough

A single number hides three things:

Which band? "Blue" can mean a narrow slice or the whole 400–500 nm range. Blocking a narrow slice near violet is easy and says little about 480 nm or green.
Which lens? The number should come from the exact lens tint you're buying, not a sister product.
Under what light? Real lamps and screens give off different mixes of colors. The 50-lens study measured every lens under five sources, including a tablet, an incandescent lamp, overhead fluorescent light and sunlight (Mason et al., 2022).

How to read a lens lab report: the other numbers

Lab reports often include a page of standards results next to the chart. A few terms worth knowing:

Luminous transmittance (Tv or VLT): how much visible light gets through overall, weighted to how bright things look. It tells you how dark a lens is, not how much blue it blocks.
Filter category (0–4): sunglass standards sort lenses by Tv. Category 0 is clear or very light (over 80%), category 2 is medium (18–43%), category 3 is dark (8–18%), and category 4 is very dark (3–8%) (College of Optometrists). A category 3 result describes a dark sunglass lens.
Twilight and night driving: under that standard, lenses that let through less than 75% of light aren't suitable for driving at dusk or at night (College of Optometrists). That rules out deep evening tints like red and amber.
UV400 / UV protection: UV protection depends on the lens material, not the color or darkness of the tint (Swiss Federal Office of Public Health). It's a separate question from blue light.
Melanopic measures: the international standard CIE S 026 defines how to measure light's effect on the body-clock sensor (CIE). A report that gives a melanopic figure is speaking the language sleep researchers use.

Red flags and questions to ask any brand

Does the report name the product? Look for the brand, model or lens name you're buying. A report for an unnamed lens, a different brand or a sunglass model doesn't tell you about this one.
Who did the testing, and when? Look for an identified lab and a date.
Does the curve match the color? A red lens should look low through blue and green and climb late. A flat, low line across every color is a grey sunglass tint.
Is there a full curve, or just one number? Ask for the chart.
Are certificates about the lens or the factory? A quality-management certificate (like ISO 9001) covers a company's processes, not how a lens filters light.

Where Melavue fits

We make two lenses for two times of day: DayLight, a yellow lens for daytime screens, and Midnight, our deepest red lens, for the last 1–3 hours before bed. For how lens color maps to time of day, see our lens color guide, red vs yellow blue light glasses and best blue light glasses for sleep.

Every pair is $59.99, comes with a hard case and a cleaning cloth, ships free on orders over $69.99, and has 30-day returns.

Shop Midnight → · Shop DayLight →

FAQ

How do you read a lens transmission chart?

Wavelength runs along the bottom, from violet and blue on the left to red on the right, and the percentage of light that gets through runs up the side. The lower the line, the more the lens blocks. For sleep, check the blue-to-green range, roughly 455 to 560 nm.

What wavelengths should blue light glasses for sleep block?

The body-clock sensor is most sensitive around 480 nm, and researchers count roughly 455 to 560 nm as the range that affects the body clock. A good evening lens keeps the line low through blue and into green.

Do clear blue light glasses block much blue light?

Not much of the light that matters for sleep. In one test, clear lenses with a blue reflective coating let through 76.5% to 92.2% of body-clock light. Red and orange lenses let through far less.

What does luminous transmittance mean on a lens report?

It's how much visible light gets through overall, weighted to how bright things look. It tells you how dark the lens is, not how much blue it blocks. Sunglass standards use it to sort lenses into filter categories 0 to 4.

What should a blue light glasses lab report include?

The product or lens name you're buying, an identified lab, a test date, and a full transmission curve, not just one percentage. The curve should match the lens color: a red lens should stay low through blue and green.