When two projector lumen figures can be compared: ANSI and ISO lumens versus "light source" lumens
Shopping for a projector to connect to a PC, you find a marketplace listing at 12,000 lumens and a known brand at 2,700, with the supposedly four-times-brighter one costing less. In most cases those two numbers are not on the same scale at all. The Data Projector Group of JBMIA, the Japanese industry association for business machines, publishes a page that tackles this head on: it separates brightness measured to an international standard from brightness measured to each maker's own criteria, and names the latter explicitly - LED lumens, laser lumens, light source lumens, ISO lumens and lux. It adds that such figures are generally larger than the standards-based brightness. This guide splits the notations into comparable and non-comparable, and shows exactly what string to look for on a specification sheet. This site has taken no illuminance measurements and names no products or prices.
Published · Updated · FaultNote editorial policy
Who this guide is for and what to prepare
- Readers wondering whether the lumen figures on two projector listings can be compared at all
- Readers who have seen an extraordinarily large lumen figure and want to test it
- Readers who want a sense of how much brightness their room needs
What you need
- Have the specification sheets of the candidate projectors open, footnotes included
- Note your room conditions: daytime use, ability to block light, intended image size
- Note the output on the PC side that will feed it (HDMI or USB-C)
1. The same unit, different rulers
The industry body itself acknowledges the problem. JBMIA's Data Projector Group writes: "Many models are available on the market, but one of the most essential factors in selecting a projector is the 'brightness' that the projector can project." And then: "Even if the specs are the same, the brightness may be completely different when you see the projected image."
It gives the reason: "Why does this happen? This is because manufacturers sometimes use different standards or unique measurement methods." And the conclusion: "Since the concept of the brightness standard differs, the higher number on the specs does not always mean it is brighter, making a correct comparison impossible."
So the unit may be lumens in both cases while the quantity measured is not the same. The page says as much: "The unit for projector brightness is 'lumens (lm).' On the other hand, lumens are also a unit of physical brightness, and sometimes the brightness specifications of products are measured differently from international standards."
The standards-based method is spelled out: "Lumens, which indicate a projector's brightness, are calculated by multiplying the average of the illuminance lux at the nine center points of each of the nine segments of the projection screen by the projection area." That is, the light that actually lands on the screen, represented by the average of nine points. JBMIA calls this "the most reliable brightness".
2. Which notations can be compared, and which cannot
JBMIA's page lists the notations unsuitable for comparison, and this is the most directly usable part of it.
It says: "The following are the measurements made by each company according to their own standards, distinct from international standards, and are unsuitable for comparing projectors." Then: "Examples: LED lumens, Laser lumens, Light Source lumens, ISO lumens, Lux (Lx)" - and adds that the value "may be significantly higher than the brightness based on international standards, such that it cannot be compared".
Note what is on that list: ISO lumens. The presence of the letters ISO does not by itself mean the figure is standards-based. What separates the two is whether the standard is named with its edition - ISO/IEC 21118 or JIS X 6911.
So what should you look for? JBMIA gives the literal strings: "To avoid selecting the wrong projector, we recommend checking the manufacturer's website to see if the brightness is shown based on international standards. Example: ISO/IEC 21118:2020 compliant, JIS X 6911:2021 compliant." Finding wording in that shape, in the specification sheet or a footnote, is the procedure.
On how ANSI lumens relate to the ISO/IEC figure, JBMIA's page names only ISO/IEC 21118 (Japanese Standard: JIS X6911) and does not mention ANSI. Epson's explanatory column states that there are two measurement methods, the ANSI standard (ANSI IT7.228) and the ISO/IEC standard (ISO/IEC 21118), that the ISO/IEC method does not differ from the ANSI one, and that measurements of the same product therefore agree under either. That is one manufacturer's explanation rather than the standard text, and this site has not verified the equivalence independently.
Scroll horizontally to see the full table →
| Notation on the specification sheet | How JBMIA treats it | Comparable with another maker's figure? | String to look for |
|---|---|---|---|
| Lumens, stated as compliant with ISO/IEC 21118 | International standard; derived from nine screen segments; the most reliable brightness | Yes | Wording such as ISO/IEC 21118:2020 compliant, with the edition |
| Lumens, stated as compliant with JIS X 6911 | The Japanese standard name for the same content; the more common label in Japan | Yes | Wording such as JIS X 6911:2021 compliant, with the edition |
| ANSI lumens | Not mentioned on JBMIA's page | Epson's explanation says the measurement method does not differ from the ISO/IEC one (not verified here) | Whether a standard name such as ANSI IT7.228 is given alongside |
| Light source lumens | A maker's own criterion; unsuitable for comparison | No | If this phrase appears, the figure is not the standards-based one |
| LED lumens / laser lumens | The same | No | The same |
| ISO lumens, with no standard number | The same - it appears on JBMIA's list of notations unsuitable for comparison | No | The letters ISO are not enough; look for the standard name with its edition |
| Lux (Lx) | The same | No | A different quantity entirely |
3. What ISO/IEC 21118 actually specifies
Since the advice is to look for a standard name, it is worth knowing what that standard is. The following is from ISO's catalogue page, read on 2026-09-20.
The number and title are ISO/IEC 21118:2020, "Information technology — Office equipment — Information to be included in specification sheets for data projectors", Edition 3, published 2020-02. The status is Published, and the page states: "This publication was last reviewed and confirmed in 2025. Therefore this version remains current." At the same time its stage reads "International Standard to be revised [90.92]" - a revision is in prospect. The committee is ISO/IEC JTC 1/SC 28 (Office equipment) and the document runs to 23 pages.
The catalogue abstract states the scope: "This document specifies the information to be included in the specification sheets for front projection type data projectors and the form of specification sheets." And: "This document is not applicable to units for a rear screen projection." In other words it governs what a front-projection projector's specification sheet must contain and the form it takes; rear-screen units are out of scope.
One thing to be straight about: the standard text is sold, and the catalogue page shows a price. This site has not purchased or read it. So the description of the nine-segment measurement, and anything else about the procedure, comes from JBMIA's published page, not from the standard's own text. The Japanese standard JIS X 6911 has likewise not been read here.
Scroll horizontally to see the full table →
| Field | As shown on the ISO catalogue page (2026-09-20) |
|---|---|
| Number and edition | ISO/IEC 21118:2020, Edition 3 |
| Publication date | 2020-02 |
| Status | Published; reviewed in 2025 and confirmed as remaining current |
| Stage | International Standard to be revised [90.92] |
| Scope | Information to be included in specification sheets for front projection type data projectors, and the form of those sheets |
| Out of scope | Units for rear screen projection |
| Committee and length | ISO/IEC JTC 1/SC 28; 23 pages |
4. How much brightness a room needs (as a maker's guidance)
The standard does not answer "how many lumens do I need" - it governs how figures are stated, not what is recommended. For a sense of scale, a maker's published guidance is what is available.
Epson's home-projector column, dated 19 January 2024, gives figures by viewing scenario: around 3,000 to 4,000 lumens for a bright room in the daytime, whether for a large picture or as a second screen for a PC; around 2,000 to 3,000 for evening viewing with the room lights on; around 1,000 with indirect or dimmed lighting; and around 500 to 1,000 for viewing in a bedroom before sleep. For the 200 to 500 lumen figures common on portability-focused models, it says brightness may be insufficient and suggests at least around 1,000 lumens for comfortable viewing.
Two things to keep in mind when using these numbers. First, this is a column on the website of a company that sells home projectors, and its later sections recommend that company's own models. It is not a neutral benchmark. Second, the article states its own premise: the figures given assume colour brightness rather than the brightness of a white screen. Those are different quantities.
Brightness also scales with image size. The same article notes that moving the projector further back makes the image larger, but the light spreads over a wider area and the image tends to get darker. How many lumens you need depends on the diagonal you intend to project, not only on the room.
This site has not measured projector illuminance and has not verified these figures. They are offered as one input, with their source stated.
Scroll horizontally to see the full table →
| Viewing scenario | Figure given in Epson's column | Caveat |
|---|---|---|
| Bright room in daytime; PC second-screen use | Around 3,000 to 4,000 lumens | Assumes daylight entering the room |
| Evening, room lights on | Around 2,000 to 3,000 lumens | No daylight, but lit |
| Evening, indirect or dimmed lighting | Around 1,000 lumens is described as sufficient | The same |
| Bedroom, before sleep | Around 500 to 1,000 lumens | Too bright is said to risk affecting getting to sleep |
| Portability-focused models | 200 to 500 lumen models may be insufficient; at least around 1,000 suggested | As stated in the same column |
5. The order to check in before buying
Turning all of that into a shortlisting procedure.
First, look for a standard name on each candidate's specification sheet: ISO/IEC 21118 or JIS X 6911, with the edition. JBMIA's stated examples are ISO/IEC 21118:2020 compliant and JIS X 6911:2021 compliant. It is often in small print in a footnote, so do not decide from the specification table alone.
Second, decide that any product without a standard name is simply not placed alongside the others. Discounting the number by some factor to make it comparable does not work. JBMIA says such figures are generally larger than standards-based ones, but publishes no conversion factor - and since each maker's criterion differs, no single factor could exist. This site publishes none either.
Third, having narrowed to products with a named standard, decide the figure you need from your room conditions and the image size. The guidance in section 4 is a maker's, not an absolute benchmark.
Fourth, check the things that are not brightness. For PC use, the input connectors (HDMI or USB-C), supported resolution and how latency is handled are separate axes. The underlying habit - distinguishing a number that carries a certification name from one that does not - is the same one used when reading monitor HDR tiers, which this site covers for that product category.
Scroll horizontally to see the full table →
| Step | Where to look | What to do when it fails |
|---|---|---|
| Look for the standard name | The specification table and its footnotes | Is ISO/IEC 21118 or JIS X 6911 given with its edition? |
| Narrow the comparison set | Only products where the standard name was found | Do not line up unnamed figures against others, and do not convert them |
| Decide the brightness you need | How well the room can be darkened, and the image size | A larger image spreads the light and looks darker |
| Check the non-brightness items | Input connectors, resolution, throw distance | For PC use, connectors and resolution bite first |
Limitations and requirements
- This site has not measured projector illuminance. There are no measurements in this guide, and no product names or prices.
- "ISO lumens" appears on JBMIA's list of notations unsuitable for comparison. Do not treat the letters ISO alone as evidence of standards compliance.
- The text of ISO/IEC 21118 is sold, and this site has not purchased or read it. The description of the nine-segment method comes from JBMIA's published page, not from the standard. JIS X 6911 has not been read either.
- A figure with no standard name cannot be made comparable by applying some discount factor. Because each maker's criterion differs, no single conversion factor exists.
- The per-scenario guidance in section 4 comes from a column on the website of a company that sells home projectors, and is not a neutral benchmark. Its later sections recommend that company's own models.
- That same column states that its figures assume colour brightness rather than the brightness of a white screen.
- ISO/IEC 21118:2020 sits at the catalogue stage "International Standard to be revised". The edition may change.
Frequently asked questions
Is a 12,000-lumen marketplace projector brighter than a 2,700-lumen one from a known brand?
If the specification sheet gives no standard name, the figures cannot be compared. JBMIA lists LED lumens, laser lumens, light source lumens, ISO lumens and lux as examples of measurements made to each company's own criteria, and says such values may be significantly higher than standards-based brightness. Start by checking both sheets for ISO/IEC 21118 or JIS X 6911 with an edition.
Can I treat ANSI lumens and ISO/IEC lumens as the same thing?
JBMIA's page names only ISO/IEC 21118 (Japanese Standard: JIS X6911) and does not mention ANSI. Epson's column states that the ISO/IEC measurement method does not differ from the ANSI one and that results for the same product agree under either. That is one manufacturer's explanation; this site has not confirmed it against the standard text.
What does a "light source lumens" figure measure?
JBMIA lists it as an example of a measurement made to a company's own criteria, distinct from international standards and unsuitable for comparing projectors. It also explains that because lumens are also a unit of physical brightness, brightness measured differently from the standards is sometimes presented as a product specification. This site has found no primary source defining precisely what such a figure measures, so it does not describe the method.
How many lumens is enough?
The standard does not set a required value; it governs what a specification sheet contains and its form. As guidance, Epson's column suggests around 3,000 to 4,000 lumens for a bright daytime room, around 2,000 to 3,000 for the evening with lights on, around 1,000 with the lights down, and 500 to 1,000 for a bedroom. Weigh it knowing it is a maker's guidance and that its figures assume colour brightness. The same article also notes that a larger projected image spreads the light and looks darker.
Where on the specification sheet do I find the standard name?
Often in small print in a footnote rather than in the specification table itself. The examples JBMIA gives take the form ISO/IEC 21118:2020 compliant or JIS X 6911:2021 compliant. If no string of that shape can be found, the decision is to keep that figure out of the comparison.
Sources and verification date
Sources checked: . These sources support the specifications, procedures or prices discussed here. Check each source for applicable conditions and current information.
- JBMIA (Japan Business Machine and Information System Industries Association), Data Projector Group: projector brightness notation, Japanese edition. The statement that manufacturers sometimes use different standards or their own measurement methods so a correct comparison is impossible; ISO/IEC 21118 (Japanese Standard: JIS X6911) as the international standard with the nine-segment calculation; the examples of notations unsuitable for comparison (LED lumens, laser lumens, light source lumens, ISO lumens, lux); and the recommended strings to look for. Read 2026-09-20 ↗
- JBMIA Data Projector Group: projector brightness notation, English edition. The same content in English, and the source of the quotations in the English edition of this guide. Read 2026-09-20 ↗
- ISO: ISO/IEC 21118:2020 catalogue page. Title, Edition 3, publication date 2020-02, Status Published, the note that the publication was last reviewed and confirmed in 2025 so the version remains current, Stage International Standard to be revised [90.92], the abstract (specification-sheet information and form for front projection type data projectors; not applicable to rear screen projection), ISO/IEC JTC 1/SC 28, 23 pages. The standard text is sold and was not purchased or read. Read 2026-09-20 ↗
- Epson Japan: a column on choosing projector lumens by viewing scenario, article date 19 January 2024. The statement that there are two measurement methods, ANSI (ANSI IT7.228) and ISO/IEC (ISO/IEC 21118), with the same method and agreeing results; the per-scenario lumen figures; the note that the figures assume colour brightness rather than white-screen brightness; and the relationship between image size and brightness. A manufacturer's own column whose later sections recommend its own products. Read 2026-09-20 ↗
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