2-4.Focal Length and Focal Diameter of Halogen Point Heater

Relationship with the light condensing diameter of the Halogen Point Heater

First of all, we will define the terms.

Focal length: Distance from the end of the condensing mirror to the object to be heated
Focal diameter: The maximum temperature at the centre of the focal length is 100%, and the temperature range is 100% to 80%.
Light condensing diameter: The temperature of the centre at any length is 100%, and the temperature range is 100% to 80%.
The “Focal length” of the rated value of the Condensing mirror is the length at which the “Focal diameter” reaches the maximum temperature.

(1) Relationship between focal diameter and electric power (W)
The larger the electric power (W), the larger the focal diameter.
If the voltage is the same at the same focal length, the output density does not change even if the electric power (W) changes.
The larger the electric power (W), the larger the Focal diameter, and the smaller the electric power (W), the smaller the Focal diameter.

(2) Relationship between focal diameter and heating filament
The focal diameter cannot be smaller than the heating element. The cross section of the stereoscopic image of the heating filament is the minimum size of the focal diameter.

(3) Relationship between focal diameter and focal length
If the focal diameter is increased or decreased from the rated focal diameter, the focal diameter can be heated in a large and wide range. (Out focus)
Even if the focal length is the same, the shorter the focal length, the higher the output density, and the higher the temperature of the lamp.
* Although it is possible to manufacture a custom-made condensing mirror after a special design, from the viewpoint of price and delivery time,
It is recommended to consider whether the standard product can be used by shifting it from the focal position.

(4) Relationship between the condensing diameter and the aperture diameter of the condensing mirror
The larger the diameter of the condensing mirror, the smaller the aperture and the higher the temperature.
However, the minimum size is up to the filament diameter.

The following is a photograph of HPH-18 / f9 / 12V-40W (focal length rating 9mm, voltage 4V, power 5A), with different focal lengths.

(Fig. 1) Irradiate a model with f = 9.0 at a distance of 4.5 mm
The focal diameter is larger than the rating with an almost even distribution.

(Fig. 2) Irradiate a model with f = 9.0 at a distance of 9.0 mm
Since the focal length is a fixed position, the focal diameter (luminous flux) is the most efficient state. The focus is at maximum temperature.

(Fig. 3) Irradiate a model with f = 9.0 at a distance of 13.5 mm
The focal diameter is large, but the central part is a little strong.

(Fig. 4) Irradiate a model with f = 9.0 at a distance of 18.0 mm
The focal diameter has become large, and irradiation is possible almost evenly.

To maximize the performance of the lamp and succeed in high temperature heating, we recommend to use the “Re-reflective Heating Method”.