Luminance Contrast Calculator: The AS 1428.1 30% Rule, LRV and the Bowman-Sapolinski Equation (2025 Guide)

Luminance contrast is the one accessibility figure that cannot be read off a drawing. A door frame that looks different from the wall on a rendered elevation can fail. A pair of mid greys that seem far apart on a colour chart usually does. AS 1428.1:2021 asks for a minimum of 30% at doorways, stair nosings and the line on frameless glazing. It is calculated from the light reflectance value of each surface, with an equation that is not a subtraction. This guide sets out where the 30% applies with its clause and works the Bowman-Sapolinski equation with real numbers. It explains the measurement methods in Appendix B and covers the 45% and 60% for tactile indicators. The calculator in section 5 runs the equation for your pair.

In one minute

• Luminance contrast is the light reflected from one surface compared to the light reflected from another (AS 1428.1:2021 clause 1.4.12). The input is the luminous reflectance of each surface, the LRV, from 0 to 100.

• The equation is C = 125 (Y2 − Y1) / (Y1 + Y2 + 25), the Bowman-Sapolinski equation. Y2 is the lighter surface and Y1 the darker (Appendix B, clauses B.3.3, B.4 and B.5.3). It is a ratio: the same gap gives less contrast as both surfaces get lighter.

• 30% is the minimum at a doorway: leaf, jamb, architrave or wall, in a band at least 50 mm wide (clause 10.1). The same minimum applies at a stair nosing strip, 50 to 75 mm deep and one colour (clause 8.1(f)). It applies on the line across frameless glazing, against the floor within 2 m (clause 3.6). And it applies on an accessible toilet seat (clause 12.2.3(e)).

• Tactile ground surface indicators need more, measured against the adjacent path of travel. The figures are 30% integrated, 45% discrete, and 60% for the contrasting part of composite discrete units (AS/NZS 1428.4.1:2009 clause 2.2(b)).

• The NCC calls up the Standard through Volume One D4D4(1)(a). It calls up clause 7 of AS 1428.1 for ramps and clause 8 for stairways. For fire-isolated stairways it calls up 8.1(f) and (g), the nosing strip. NCC 2022 Amendment 2 adopted AS 1428.1:2021. NCC 2025 lists the same edition.

1. What luminance contrast is

AS 1428.1:2021 defines luminance contrast as "the light reflected from one surface or component, compared to the light reflected from another surface or component" (clause 1.4.12). The NCC glossary carries the same words. The quantity behind it is luminous reflectance, usually written LRV. It is the fraction of the light falling on a surface that comes back off it, from 0 to 100.

Hue does not enter into it. A saturated red and a mid grey can have the same LRV and, to the Standard, the same luminance. That is why a "contrasting colour" chosen by eye so often fails.

The reason for the rule is in the informative Appendix C. A person with reduced contrast sensitivity may not see an unmarked step or a glass wall. Adding luminance contrast at a nosing or as a visual indicator on glazing compensates for it (C.5). Loss of depth perception has the same effect on stairs and the same remedy (C.7).

2. Where the 30% applies

Each clause names the pair of surfaces to be compared. The pairing matters as much as the number, because contrast is a property of two surfaces, not one.

• Doorways (clause 10.1). Every doorway must have a minimum luminance contrast of 30% between one of five pairs. The pairs are: door leaf and jamb; leaf and adjacent wall; architrave and wall; leaf and architrave; or jamb and adjacent wall. The contrasting area must be at least 50 mm wide. The note gives the objective: that a person with low vision can find the doorway in the wall. One pair is enough. A dark leaf in a pale wall passes even if the frame matches the wall.

• Stair nosings (clause 8.1(f) and (g)). Each tread must have a single strip, not a multistrip, 50 to 75 mm deep across the full width of the path of travel. It must be one continuous colour, with a minimum luminance contrast of 30% to the background. It must be set back no more than 15 mm from the front of the nosing. Where it is not set back, any area of luminance contrast may not extend more than 10 mm down the riser (8.1(g)).

• Frameless and fully glazed doors and sidelights (clause 3.6). Where there is no chair rail, handrail or transom, the glazing carries an unbroken, solid and opaque contrasting line. The line is at least 75 mm high across its full width, with its lower edge 900 to 1 000 mm above the finished floor. It must give 30% luminance contrast when viewed from each side against the floor surfaces within 2 m of the glazing on the opposite side. Note 1 lets tinted glass be judged against the tint instead.

• Accessible toilet seats (clause 12.2.3(e)). A minimum of 30% with the pan, the wall, or the floor against which the seat is viewed. NCC Volume One repeats it for the pan in an accessible adult change facility (S27C4(3)).

The NCC adds a few of its own at the same figure:

• Braille and tactile signs. The background or 5 mm border needs 30% to the mounting surface, and the characters need 30% to the sign. Both are judged under the lighting in which the sign is read (Volume One S15C4).

• The entrance door of an accessible adult change facility, with the Standard's five pairs (S27C9).

• Obstacles abutting an accessway in a public transport building (I2D2(5)).

3. The Bowman-Sapolinski equation, and why it is not a subtraction

Appendix B of AS 1428.1:2021 is informative. But it is the only method the Standard gives, and every 30% clause points to it. Its central line is the Bowman-Sapolinski equation, printed in B.3.3, B.4 and B.5.3:

C = 125 (Y2 − Y1) / (Y1 + Y2 + 25)

where C is the luminance contrast in per cent, Y1 the luminous reflectance of the darker surface and Y2 that of the lighter (B.4). The numerator is the difference you would expect. The denominator, the sum of the two values plus 25, is what makes the equation behave. Two dark surfaces with a small sum give a large contrast from a modest difference. Two light surfaces need a much bigger difference for the same figure.

Darker surface Y1	Lighter surface Y2	Difference	Working	Contrast	Against 30%
LRV 20	LRV 70	50	125 × 50 / (20 + 70 + 25) = 6 250 / 115	54.3%	Passes
LRV 40	LRV 70	30	125 × 30 / (40 + 70 + 25) = 3 750 / 135	27.8%	Fails
LRV 5	LRV 30	25	125 × 25 / (5 + 30 + 25) = 3 125 / 60	52.1%	Passes
LRV 38	LRV 70	32	125 × 32 / (38 + 70 + 25) = 4 000 / 133	30.1%	Passes, just

The equation applied to four pairs. A 25-point gap between two dark surfaces gives 52%; a 30-point gap between two lighter surfaces gives 28%.

Three consequences follow.

• Against a given background, there is a ceiling LRV for a darker element and a floor for a lighter one. Solving for 30% against LRV 70 gives about 38 darker. Against LRV 30 it gives about 13 darker or 57 lighter. These figures are calculated from the equation. Appendix B tabulates the limits in Table B.1 and draws them in Figure B.1, which is the table to cite.

• A lighter element cannot reach 30% against a light background at all. At LRV 70 it would need an LRV above 100.

• The equation is symmetric. Swap element and background and the figure is the same.

4. Measuring the LRV: the three methods in Appendix B

B.2 sets the frame:

• The first building element should have a minimum luminance contrast of 30% compared to the second.

• It may be necessary to test both wet and dry.

• Either the contact or the non-contact method may be used.

B.3, the non-contact method. The instrument is a tristimulus colorimeter or a spectrophotometer with diffuse illumination and normal viewing geometry, under CIE Standard Illuminant D65. It reads the tristimulus value Y of the surface, which is the luminous reflectance (B.3.2). Readings are taken in at least five locations on each element, or on five units of the product. At least ten are taken where the surface does not look uniformly coloured. Unless wetting is inappropriate, the surface is then kept wet for five minutes, blotted and read again. The mean dry and wet values are recorded (B.3.3).

The method does not suit translucent or illuminated surfaces (B.3.1). Note 1 to B.3.1 is the practical point: some manufacturers publish luminous reflectance values. A value measured this way is the number to ask a supplier for.

B.4, calculating from known values. Where both luminous reflectances are known, B.4 is the equation with Y1 the darker surface and Y2 the lighter. It is read against Table B.1 and Figure B.1. This is the design-stage check and what the calculator below does. A supplier's measured LRV is a fact. An LRV read off a colour notation is an estimate. One guessed from a rendering is not a measurement.

B.5, the contact method. This is the on-site method, under the prevailing lighting. It is the only one that works on a surface that is not uniformly coloured (B.5.1). It uses a luminance meter with a 1 degree field approximating the CIE 1931 standard observer (B.5.2). The meter is mounted on a tripod with the lens at 1.6 m plus or minus 0.1 m, the eye height of a standing person. It is placed so both elements can be read without moving it, and aimed where the smaller element just fills the field (B.5.3(a) to (c)).

The same equation gives the contrast (B.5.3(d)). The report describes the light sources, with separate figures where day and night differ (B.5.4). A frame in a shadowed reveal and the same frame under a downlight can return different figures, which is the intent. The NCC's sign clause likewise requires the contrast under the lighting in which the sign is read (S15C4).

5. Check a pair of surfaces

Set the light reflectance value of each surface and choose the requirement. The drawing fills a door frame and its wall in the greys those LRVs produce. The bar shows the achieved figure against the minimum. The same calculation is in the free luminance contrast calculator, with a printable receipt and a link to ask AEC Assistant about the result.

The strip below makes the ceiling visible. Against a background of LRV 70, every element up to LRV 38 passes and everything lighter fails. That includes a white at LRV 95, 25 points away but only 16%.

6. Tactile ground surface indicators: 30%, 45% and 60%

AS 1428.1 hands tactile ground surface indicators to a separate Standard. TGSIs to warn people of hazards must be in accordance with AS/NZS 1428.4.1 (Section 6). AS/NZS 1428.4.1:2009 sets three thresholds in clause 2.2(b), against the base surface, tested to its Appendix E:

• Not less than 30% across the entire area for integrated TGSIs of the same colour as the underlying surface (2.2(b)(i)).

• Not less than 45% for discrete TGSIs, the individual studs and bars (2.2(b)(ii)).

• For discrete TGSIs made of two colours or materials, a section of the raised surface with 60% contrast for a diameter of 25 mm plus or minus 1 mm (2.2(b)(iii)).

Appendix E2 restates the three against the surface of the adjacent path of travel. The 45% is for discrete units whose sloping sides and top share one luminance. The 60% is for composite units whose sides and top differ.

The equation is the same one. E3.4 calculates the contrast of a tactile indicator and its surround with C = 125 (Y2 − Y1) / (Y1 + Y2 + 25), named as the Bowman-Sapolinski equation. E4 sets each threshold as that equation equal to 30, 45 or 60.

E4 also states what the higher thresholds force. Where the surround has a luminous reflectance above 40, discrete units lighter than it can never provide sufficient contrast. A surround above 55 cannot be adequately contrasted by integrated units. On a pale concrete path the studs are dark, or they do not comply. AS/NZS 1428.4.1:2009 remains the current TGSI Standard.

7. Where the NCC calls it up, and which edition applies

The Deemed-to-Satisfy route into AS 1428.1 for a Class 2 to 9 building is Volume One Part D4. In a building required to be accessible, every ramp and stairway not exempted by D4D5 must comply with AS 1428.1 as follows (D4D4(1)(a)):

• Clause 7 for a ramp other than a fire-isolated ramp.

• Clause 8 for a stairway other than a fire-isolated stairway.

• Clause 8.1(f) and (g) for a fire-isolated stairway.

That last item is the nosing strip. A fire-isolated stair is otherwise outside the accessible stair rules. But its treads still carry the 50 to 75 mm strip at 30%, with the 10 mm limit down the riser. Which buildings and parts must be accessible is set by D4D2.

The nosing strip also has a second, unrelated test: slip resistance. The treads of every stairway must have a surface or a nosing strip with the slip-resistance classification in Table D3D15, tested to AS 4586 (Volume One D3D14(1)(e)). For a nosing or landing edge strip, that is P3 dry and P4 wet. A product data sheet should give both figures. The stair rules are in NCC D3D14: goings and risers explained and NCC stair requirements. The ramp side of clause 7 is in NCC ramp requirements and the 1 in 14 gradient.

On editions: NCC 2022 Amendment 2, in force from 29 July 2025, adopted AS 1428.1:2021 in place of the 2009 edition. The NCC 2025 schedule of referenced documents lists AS 1428.1:2021 as well. So the clause numbers here hold under both.

NCC 2025 took effect on 1 May 2026 in the Commonwealth, the ACT, Tasmania, Victoria and Western Australia. It applies from 1 May 2027 in New South Wales, Queensland and South Australia, and has not been adopted in the Northern Territory. See NCC 2025 changes and state adoption dates.

8. Common mistakes

• Reading the LRV difference as the contrast. A 30-point gap is not 30%. LRV 40 against 70 is 28% and fails. LRV 10 against 40 is 50%.

• Contrasting the wrong pair. A dark handle on a pale door is not one of the five pairs in clause 10.1. Clause 3.6 compares the glazing line with the floor beyond, not the wall beside the glass. Clause 8.1(f) compares the strip with the tread it sits on.

• A pale element on a pale background. Above LRV 40 for a surround, no lighter discrete TGSI can reach 45%. Above LRV 55, no integrated TGSI can reach 30% (AS/NZS 1428.4.1 E4). The same arithmetic applies to a white wall: the frame must be dark.

• A band too narrow to count, or a strip that wraps the riser. The doorway contrast must be at least 50 mm wide (10.1). A nosing strip must be 50 to 75 mm deep and one colour (8.1(f)). It must extend no more than 10 mm down the riser where it is not set back (8.1(g)).

• Trusting a colour-chart LRV. A value inferred from a colour notation is indicative only. Ask the supplier for the measured figure and, on a contested job, have the finished surfaces read on site under their own lighting (B.5).

9. Where to read the source

Both Standards are purchased from Standards Australia:

• AS 1428.1:2021 Design for access and mobility, Part 1: General requirements for access, New building work: clause 1.4.12, 3.6, 8.1(f) and (g), 10.1 and 12.2.3. Appendix B covers the methods and the equation, and Appendix C covers vision impairment.

• AS/NZS 1428.4.1:2009 Tactile indicators: clause 2.2(b) and Appendix E.

NCC 2025 Volume One D4D2, D4D4, D4D5, D3D14 and Table D3D15, and Specifications 15 and 27 are free to read on the NCC website.

Inside AEC Assistant, the Code and the Standard are searchable by clause. Ask what contrast a nosing strip needs on a fire-isolated stair, and the answer comes back with D4D4 and clause 8.1(f) cited beside it.