How to choose a headlamp: some basic knowledge before choosing a headlamp

Update:22 Feb 2021
Summary:

As a part of outdoor equipment, there are many kinds of […]

As a part of outdoor equipment, there are many kinds of headlamp. So how can you buy your own headlamp? Let's classify the headlights first
According to the classification of headlamp in the market, we can generally divide them into three categories: small headlamp, multi-purpose headlamp and special purpose headlamp.
Small headlamp: generally refers to small, very light headlamp, these headlamp easy to place in the backpack, pocket and other places, easy to take. These headlights are mainly used for night lighting and are very convenient for night activities.

Multi purpose headlamp: it generally refers to the headlamp that has a longer lighting time and a longer lighting distance than the small headlamp, but is heavier than the small headlamp. It has one or several light sources, has a certain waterproof performance, and is suitable for a variety of environments. This kind of headlamp has the best matching in size, weight and strength. Its wide range of application is not the alternative of other headlights.
Special purpose headlamp: it generally refers to the headlamp used in special environment. This kind of headlamp is the highest in terms of its own intensity, lighting distance and use time. This design concept also makes this type of headlamp more suitable for use in the relatively harsh conditions of natural environment (such as cave exploration, exploration, rescue and other activities)
In addition, we divide the headlamp into three categories according to the brightness intensity, which is measured by lumen.

Standard headlamp
(brightness < 30 lumens)
This kind of headlamp is simple in design, versatile and easy to use.
High power headlamp
(30 lumens < brightness < 50 lumens)
This kind of headlamp can provide strong lighting, and has a variety of adjustment modes: brightness, distance, lighting time, beam direction, etc.
High brightness headlamp
(50 lumens < brightness < 100 lumens)
This kind of headlamp can provide super brightness lighting, not only has strong versatility, but also has a variety of adjustment modes: brightness, distance, lighting time, beam direction, etc.
Now let's learn about light sources.
Classification of light
Generally speaking, there are three types of visible light
1. Geometrical optics: light is composed of straight rays.
2. Wave optics: light is an electromagnetic wave, only part of which can be detected by our naked eye.
3. Particle optics: light is a stream of tiny particles with zero mass, which we call photons.
According to the characteristics of the light source we want to study, we can choose any of the three types to have a deep understanding.
spectrum
The most commonly mentioned characteristic of spectrum is color, which is closely related to the length of light wave, usually we call it wavelength.
Different wavelengths make up the electromagnetic spectrum.
Wavelength is the distance between two adjacent wave vibration particles, the unit is nanometer
Wavelength spectrum type
More than 10cm --- radio wave
1 mm to 10 cm -- microwave and radar waves
1um to 500um --- infrared
400nm to 700nm --- visible light
10nm to 400nm --- ultraviolet
10-11m to 10-8m --- X-ray
10-14m to 10-12m --- gamma rays

sunlight
The sun continuously emits great energy; but only a tiny part of it can be seen by our naked eyes. The wavelength of this part of the light is between 380 nm and 780 nm, and our naked eye has different sensitivity to different color light sources, so the visible part we can detect is very few. (for example, we are very sensitive to yellow)
Artificial light source
Standard light bulbs and most LED lights can emit light source, but we can not simply think that light has only one wavelength, because it is composed of many wavelengths. In fact, white light is the result of many different wavelengths of visible light. (primary color mixing)
Basic definition
When we describe light sources, we usually use some concepts based on photometry
These concepts include: luminous flux, luminous intensity, illumination and brightness.
The four factors are interrelated as follows:
-An artificial light source, such as an electric light, can emit light in any direction.
-In a specific direction, this light has a certain luminous intensity.
-The surface of an object can absorb part of the light at a certain distance.
-The surface that is illuminated by light reflects back part of the light to the observer's direction (here we mean the eye); that's what brightness means.
Luminous flux lumen (LM)
The total amount of light emitted by the headlamp in all directions is the luminous flux.
Luminous intensity candela (CD)
Candela is used to describe the intensity of light emitted from a source in a particular direction. Generally speaking, the intensity of light emitted from different directions is different.

Illumination [degrees]-lux (lx)

   We define the luminous flux per unit area surface as illumination [degree]

   Now that we know what the luminous intensity is and the relationship between the light source and the illuminated surface, let us now calculate the illumination [degrees] by dividing the luminous intensity by the illuminated area.

  E(lx)=I(cd)/d2(m)

   Brightness-Candela per square meter (cd/m2)

  Visible brightness calculation method: Luminous intensity/visible area, specifically, the ability to reflect the brightness of the area visible to the naked eye.

  Light output-lumens per watt (lm/W)

  The amount of light output depends on the luminous flux at the light source and the power conversion rate at the light source.

   In fact, the electrical energy of a light source is not completely converted into visible light, because a considerable part of it is lost in other forms, such as heat.

   Luminous performance measurement standard

   To evaluate the performance of a headlamp, we can measure it according to four concepts: lighting distance, light durability, luminous flux, beam type

   In order to have a deeper understanding of the concepts of lighting distance, light durability, luminous flux, and beam type, let's add relevant knowledge first and see under what circumstances these data are tested:

   minimum lighting

   Before measuring the lighting distance and lighting time, when the light source cannot provide us with sufficient visibility, we need to have a specific definition to describe. Take Petzl headlights as an example (why use PETZL products as an example? Because I feel that PETZL headlights are too NB!) They conducted in-depth research on this and found that when the illuminance can appear at the same time as the light emitted by the full moon, In other words, the illumination [degree] is 0. 25 Lux, which can meet the needs of illumination, which is the minimum brightness.

   Lighting distance and lighting time test

   This test uses 5 bulbs and 2 batteries (normal batteries or rechargeable batteries) to compare the headlights we sell with the same bulbs (if the headlights do not have batteries, we recommend using high-performance alkaline batteries). Finally, we take the average value of 10 sets of tests.

  The influence of temperature

  The battery is affected by the ambient temperature, so in order to obtain a standard result, the ambient temperature of all tests is controlled at 20 degrees Celsius.

Beam type
The type of light beam depends on the type of light source and optical definition
-Wide angle beam
-Focused beam
When each kind of beam irradiates, there will be some weaker beams around the main beam. This makes the headlamp more comfortable and diversified.
Wide angle beam
Wide angle beam is suitable for short distance and slow activity: for example, camping, walking, etc.
Focused beam
A focused beam focuses light at a single point, so it can irradiate a long distance. This kind of beam is suitable for road exploration and mobile activities: running, hiking, mountaineering, etc.