Measuring the brightness of a Bi-LED projector is not as simple as reading one lumen or lux number.

A projector can produce:

• high peak lux
• a sharp hotspot
• strong cold-start output

and still have an average overall beam.

For retrofit shops, distributors and B2B buyers, a useful test should answer a more practical question:

How does this projector perform under the same test conditions compared with another projector?

That means controlling:

• distance
• voltage
• projector position
• aiming
• measurement points
• operating temperature
• test equipment

The goal is not to create the biggest number.

The goal is to produce repeatable data that helps compare projector samples fairly.

Brightness Is Not One Number

A Bi-LED projector produces a complete beam.

That beam has:

• a hotspot
• a cutoff
• width
• foreground illumination
• high-beam distribution

One number cannot describe all of these.

This is why projector evaluation usually combines:

• lux measurements
• beam-pattern inspection
• high-beam comparison
• thermal stability
• sample consistency

For the basic difference between lumen, lux and candela, see our guide to lumens vs lux vs candela in automotive lighting.

What Should You Actually Measure?

For most practical Bi-LED projector comparisons, the most useful measurements are:

Lux

Lux measures illuminance at a surface.

It tells you how much light reaches a specific point on the test wall or measurement plane.

Candela

Candela describes luminous intensity in a particular direction.

It is useful when comparing directional intensity, especially for forward reach.

Beam Distribution

This includes:

• hotspot position
• width
• cutoff
• foreground
• stray light
• high beam

Thermal Stability

The projector should also be checked after it reaches a more stable operating condition.

This is important because output can change as temperature rises.

Why Test Conditions Must Be the Same

Two projector measurements are only useful if they were taken under comparable conditions.

Differences in test setup can easily change the result.

Important variables include:

• distance
• voltage
• current
• projector height
• projector rotation
• aiming
• ambient temperature
• lux meter
• measurement point

If one projector is measured at a shorter distance, the lux number may appear much higher.

If one unit is tested cold and another after warming up, the comparison is also unfair.

Step 1: Fix the Projector in a Stable Position

The projector should not move during the test.

Use:

• a fixed bracket
• test stand
• rigid mounting fixture

The optical axis should remain consistent.

Avoid holding the projector by hand.

Even a small angle change can move the hotspot and change the lux reading.

Step 2: Use a Fixed Test Distance

Choose one test distance and keep it the same for all projector samples.

The exact distance depends on your test setup.

What matters most is consistency.

Do not compare:

• one projector tested at 5 meters
• another tested at 7.5 meters

unless the values are converted appropriately.

For B2B sample comparison, use one standardized internal test distance.

Step 3: Use a Stable Power Supply

Projector output depends on electrical input.

Record:

• voltage
• current
• power

Use the same supply conditions for all samples.

Do not compare a projector tested at one voltage with another projector tested at a different voltage.

A stable DC power supply is more useful for controlled comparison than an unknown vehicle electrical system.

Step 4: Aim the Projector Correctly

The beam should be positioned consistently before measurement.

Check:

• horizontal rotation
• vertical angle
• cutoff position
• optical center

If the hotspot moves relative to the lux meter, the reading will change.

This is why aiming is part of the test procedure, not a cosmetic adjustment.

Step 5: Allow the Projector to Reach a Stable Operating Condition

Do not judge the projector only from the first few seconds after startup.

LED and driver behavior can change as temperature increases.

Run the projector until:

• output becomes relatively stable
• temperature approaches a steady operating condition
• fan behavior stabilizes

Do not use one universal warm-up time for every projector.

Different designs may stabilize at different rates.

For more detail, see our guide to Bi-LED projector thermal management.

Step 6: Measure the Hotspot

The hotspot is usually one of the brightest areas in the beam.

Place the lux meter at a defined measurement position.

Record:

• peak lux
• measurement distance
• projector voltage
• operating condition

But do not stop there.

Peak lux alone does not describe the complete beam.

A projector with a very concentrated hotspot may produce a high number but weak surrounding illumination.

Step 7: Measure More Than One Point

For a more useful comparison, measure several points.

For example:

• hotspot
• center beam
• left side
• right side
• lower foreground
• selected high-beam points

The exact test grid can vary.

The important thing is to use the same measurement positions for every projector.

This gives a better picture of beam distribution.

Why Peak Lux Is Not Enough

Peak lux is easy to market.

But it can be misleading.

Imagine two projectors.

Projector A

• very high center hotspot
• narrow beam
• weak side illumination

Projector B

• slightly lower peak lux
• wider beam
• smoother distribution

Projector A may win if you compare only one lux number.

Projector B may provide the more useful road beam.

This is why B2B buyers should evaluate:

intensity + distribution

rather than intensity alone.

How Is Candela Related to Lux?

When distance is known, lux can be used to estimate directional intensity.

In simplified form:

Candela ≈ Lux × Distance²

where distance is measured in meters.

For example, if a specific point measures:

100 lux at 10 meters

the approximate luminous intensity in that direction would be:

100 × 10² = 10,000 cd

This relationship is useful for controlled directional comparison.

But the measurement must be made under consistent conditions.

When Are Lumens Useful?

Lumens describe total luminous flux.

They can be useful when evaluating the total light output of a light source or module.

However, lumens do not tell you:

• where the beam goes
• how strong the hotspot is
• how wide the beam is
• whether the cutoff is controlled

For projector evaluation, lumen data should therefore be combined with optical measurements.

Integrating Sphere Measurements

An integrating sphere can be used to measure total luminous flux.

This is useful when you want to understand the total output of:

• LED source
• module
• complete optical system

But an integrating sphere does not replace wall-beam testing.

A projector is an optical system.

Two projectors with similar lumen output can produce very different beam patterns.

Beam Pattern Still Matters

A brightness test should always be combined with beam evaluation.

Look at:

• cutoff
• hotspot
• width
• foreground
• uniformity
• stray light
• high beam

For a full optical checklist, see our guide to what makes a good Bi-LED projector beam pattern.

Low Beam and High Beam Should Be Tested Separately

A Bi-LED projector performs two beam functions.

That means both should be measured.

Low Beam

Check:

• hotspot
• cutoff
• width
• distribution
• foreground

High Beam

Check:

• forward intensity
• vertical extension
• center reach
• overall spread

A projector with a strong low beam may still have an average high beam.

Cold Output vs Stabilized Output

This is one of the most useful tests for B2B sourcing.

Record the projector at:

• startup
• intermediate warm-up
• stable operating condition

Then compare output.

You are looking for:

• how much the output changes
• whether it stabilizes
• whether there is flicker
• whether the driver reduces power significantly

Do not automatically assume that any output reduction means poor quality.

Some drivers use thermal protection.

The important question is whether the stabilized output remains acceptable.

Why Camera Photos Are Not Enough

Beam photos are useful for visual comparison.

But camera settings can change the appearance dramatically.

Automatic exposure can make:

• hotspot look brighter
• cutoff look sharper
• surrounding beam look darker

If using beam photos, keep these settings consistent:

• ISO
• shutter speed
• exposure
• white balance
• camera position

Do not use one auto-exposure photo to compare two products professionally.

Common Testing Mistakes

Testing at Different Distances

This makes lux numbers difficult to compare.

Testing at Different Voltages

Electrical input directly affects output.

Measuring Only Peak Lux

This ignores beam distribution.

Comparing Cold and Warm Projectors

One projector may have already stabilized while another is still at maximum cold output.

Moving the Projector Between Measurements

A small angle change can affect the result.

Using Different Lux Meters

Different meters may have different calibration or response.

Trusting Advertised Lumen Numbers Alone

Lumen claims do not show real beam distribution.

Using Camera Brightness as Measurement Data

A photo is not a calibrated lux measurement.

Can One Lux Number Define a “Good” Bi-LED Projector?

No.

There is no universal lux number that automatically proves a projector is good.

The result depends on:

• test distance
• measurement point
• beam design
• supply voltage
• temperature
• equipment

So statements such as:

“A good projector must produce more than X lux”

should be treated cautiously unless the full test method is specified.

Does Higher Lux Always Mean Better Night Driving?

No.

Lux is useful, but road performance depends on beam distribution.

A projector with higher peak lux may still have:

• poor width
• dark zones
• excessive foreground
• weak high beam

A more balanced projector can sometimes be more useful even with lower peak intensity.

What Should B2B Buyers Record During Sample Testing?

A simple test record can include:

Item	Record
Projector model	Model / SKU
Voltage	V
Current	A
Power	W
Test distance	m
Cold peak lux	Lux
Warm peak lux	Lux
Hotspot position	Notes
Beam width	Notes
Low beam	Photo + data
High beam	Photo + data
Fan behavior	Notes
Sample consistency	Pass / Review

This makes supplier comparisons much easier.

Test Several Samples, Not Just One

For bulk sourcing, one good projector sample is not enough.

Where practical, compare several units.

Look for consistency in:

• hotspot position
• peak lux
• cutoff
• high beam
• fan behavior
• electrical input

This helps identify production variation.

For distributors, repeatability is often more important than one exceptional sample.

What Data Should Buyers Ask Suppliers For?

Useful data can include:

• test voltage
• current
• power
• measurement distance
• peak lux
• beam photos
• warm-output data
• thermal test conditions
• sample quantity
• LHD/RHD version

If a supplier gives only:

“12,000 lumens”

without test conditions, that number is difficult to evaluate.

How Brightness Testing Connects to Projector Selection

Brightness is only one part of projector selection.

A B2B buyer also needs to consider:

• mounting
• lens size
• body depth
• beam pattern
• thermal design
• LHD/RHD version
• supply consistency

For the full selection process, see our guide to choosing a Bi-LED projector lens.

Does a Brightness Test Prove ECE or DOT Compliance?

No.

A lux meter test or wall-beam test does not by itself prove regulatory compliance.

Regulatory testing may require:

• defined photometric points
• specified test conditions
• maximum and minimum intensity limits
• beam geometry
• complete device evaluation

For more detail, see our guide to E-mark, UNECE and FMVSS 108 for aftermarket projectors.

Frequently Asked Questions

Should I measure a Bi-LED projector in lumens or lux?

Both can be useful, but lux is usually more practical for comparing beam intensity at defined points.

Is peak lux the most important number?

No.

Beam distribution and stabilized output also matter.

How far should I place the projector from the wall?

There is no single universal distance for every B2B test setup. Choose a fixed distance and use it consistently.

How long should I warm up a Bi-LED projector?

Run it until output and thermal behavior approach a stable condition rather than using one fixed time for every product.

Does higher wattage mean higher lux?

Not necessarily.

Optical efficiency and beam design also affect intensity.

Can two 45 W projectors produce different lux readings?

Yes.

Different optical designs can create very different beam intensity and distribution.

Can I compare lux numbers from two different suppliers?

Only if the test conditions are comparable.

Does lux prove road performance?

No.

Lux should be evaluated together with beam pattern and distribution.

Should high beam be measured separately?

Yes.

Bi-LED low beam and high beam should be evaluated independently.

Does a good lux result mean the projector is legally compliant?

No.

Regulatory compliance requires specific testing and documentation.

Measure the System, Not Just the Number

A good Bi-LED projector test should not chase the highest lux value.

The most useful comparison combines:

• controlled test conditions
• multiple lux points
• low-beam distribution
• high-beam performance
• thermal stability
• sample consistency

For B2B buyers, repeatable data is more valuable than a dramatic marketing number.

Royalin works with automotive lighting suppliers in China to support overseas retrofit shops and distributors with Bi-LED projectors, brackets and vehicle-specific retrofit components.

When comparing supplier samples, our focus is on practical specifications, repeatable testing and product consistency rather than headline brightness claims alone.