Method of dynamically adjusting display luminance flux in wearable heads-up displays

1. A method of operating a wearable heads-up display that in use is worn on a head of a subject user, the method comprising:

projecting light to an eye of the subject user;

detecting an ambient light condition in at least a portion of an environment of the wearable heads-up display by an ambient light sensor;

determining a pupil size of the eye of the subject user;

determining a target luminous flux of the light projected to the eye of the subject user based on the ambient light condition detected by the ambient light sensor and the determined pupil size; and

adjusting a current luminous flux of the light projected to the eye of the subject user based on the determined target luminous flux.

2. The method of claim 1 , wherein projecting light to an eye of the subject user comprises generating a visible portion of the light by at least one visible light source and scanning the visible portion of the light over at least a portion of the eye by at least one scan mirror.

3. The method of claim 1 , wherein projecting light to an eye of the subject user comprises generating an infrared portion of the light by at least one infrared light source and scanning the infrared portion of the light over at least a portion of the eye by at least one scan mirror.

4. The method of claim 3 , wherein determining a pupil size of the eye of the subject user comprises detecting reflections of infrared light from the at least a portion of the eye for a plurality of scan orientations of the at least one scan mirror.

5. The method of claim 4 , wherein determining a pupil size of the eye of the subject user further comprises determining the pupil size from the detected reflections of infrared light and corresponding scan orientations of the at least one scan mirror.

6. The method of claim 5 , wherein determining a pupil size of the eye of the subject user further comprises constructing or reconstructing a digital representation of the at least a portion of the eye from the detected reflections of infrared light and corresponding scan orientations of the at least one scan mirror.

7. The method of claim 6 , wherein determining a pupil size of the eye of the subject user further comprises isolating a pupil region of the digital representation and determining the pupil size from the pupil region.

8. The method of claim 7 , wherein determining the pupil size from the pupil region comprises at least one of determining a diameter of the pupil region and determining an area of the pupil region.

9. The method of claim 1 , wherein determining a target luminous flux based on an output of the at least one ambient light sensor and the determined pupil size comprises selecting a target display luminance from a select range of display luminance based on the output of the ambient light sensor.

10. The method of claim 9 , wherein determining a target luminous flux based on an output of the at least one ambient light sensor and the determined pupil size further comprises determining the target luminous flux based on the target display luminance and the pupil size.

11. The method of claim 1 , wherein adjusting a current luminous flux of the light projected into the eye of the subject user based on the target luminous flux comprises adjusting the current luminous flux to match the target luminous flux.

12. The method of claim 1 , wherein projecting light to an eye of the subject user comprises generating the light by at least one light source and scanning the light over at least a portion of the eye by at least one scan mirror, and wherein adjusting a current luminous flux of the light projected to the eye of the subject user based on the target luminous flux comprises measuring the current luminous flux of the light projected to the eye of the subject user.

13. The method of claim 12 , wherein measuring the current luminous flux of the light projected to the eye of the subject user comprises directing at least a portion of the light projected to the eye of the subject user towards a photodetector and determining a value of the current luminous flux from an output of the photodetector.

14. The method of claim 13 , wherein adjusting a current luminous flux of the light projected to the eye of the subject user based on the target luminous flux further comprises modulating a drive current to the at least one light source based on a difference between the measured current luminous flux and the target luminous flux.

15. The method of claim 13 , wherein adjusting a current luminous flux of the light projected to the eye of the subject user based on the target luminous flux comprises directing at least a portion of the light towards a variable optical attenuator and controlling the variable optical attenuator to attenuate the at least a portion of the light based on a difference between the measured current luminous flux and the target luminous flux.

16. A wearable heads-up display having a field of view, comprising:

a support frame that in use is worn on a head of a subject user;

a scanning light projector carried by the support frame, the scanning light projector to project light to an eye of the subject user, the scanning light projector comprising at least one light source to generate the light and at least one scan mirror to scan the light over the eye of the subject user;

an ambient light sensor carried by the support frame, the ambient light sensor positioned and oriented to detect an ambient light condition in at least a portion of an environment of the wearable heads-up display;

a processor carried by the support frame; and

a non-transitory processor-readable storage medium communicatively coupled to the processor, wherein the non-transitory processor-readable storage medium stores data and/or processor-executable instructions, that when executed by the processor, causes the wearable heads-up display to:

determine an ambient light sensor output value representing the ambient light condition detected by the ambient light sensor from an output of the ambient light sensor;

determine a pupil size of the eye of the subject user;

determine a target luminous flux of the light projected to the eye of the subject user based on the ambient light sensor output value and the pupil size; and

adjust a current luminous flux of the light projected to the eye of the subject user based on the target luminous flux.

17. The wearable heads-up display of claim 16 , further comprising an infrared detector carried by the support frame, the infrared detector positioned and oriented to detect reflections of infrared light from the eye of the subject user.

18. The wearable heads-up display of claim 16 , further comprising a transparent combiner carried by the support frame, the transparent combiner positioned within the field of view of the wearable heads-up display, the transparent combiner including at least one of a holographic optical element and a lightguide, the transparent combiner aligned to receive the light from the at least one scan mirror and redirect the light towards the eye of the subject user when the support frame is worn on the head of the subject user.

19. The wearable heads-up display of claim 16 , wherein the scanning light projector further comprises a variable optical attenuator to selectively attenuate the light projected to the eye of the subject user in response to a control signal to adjust the current luminous flux to match the target luminous flux.

20. A method of operating a wearable heads-up display that in use is worn on a head of a subject user, the method comprising:

projecting light to an eye of the subject user;

determining a pupil size of the eye of the subject user;

determining an ambient light level based on the pupil size;

determining a target luminous flux of the light projected to the eye of the subject user based on the determined pupil size and the ambient light level; and

adjusting a current luminous flux of the light projected to the eye of the subject user based on the determined target luminous flux.