Does brighter light behave differently?

[andrewdoeshair]

Sorry if this is a dumb question, but will light act differently as it becomes brighter? I've read books on the behavior of light but I either missed this answer or it wasn't in there. I'm mostly asking out of curiousity, I don't have any practical need for this information. I suppose I could set up a little test and find out for myself, but I love hearing you all share about this stuff. I usually learn more than I asked for when I come here.
Let's say I have a 20 watt bulb behind a diffusion panel near a face, with some space and a back drop behind the head, and the face is properly exposed at whatever the camera settings may be... If I swapped it for a 40 watt bulb (assuming, but completely unsure if this is how wattage ratings work, that the brightness doubles) and then I either dropped the ISO, closed the aperture, or sped up the shutter by one stop, would I only see the the changes that would occur within the camera (like a wider DOF or less noise) or would the light itself behave differently?
I'm assuming any other ambient light in the room would of course appear darker in comparison to the brighter bulb, maybe creating more substantial shadows, but will the main light be harder or more specular than it was when it was dimmer? I keep imagining the light acting like water or air coming out of a hose, push more out and it'll smack into stuff with more force, bounce around more, get all erratic, but I have no idea if that is incorrect.

Thanks for reading.

 

[smoke665]

Not sure how to answer this on a single light, but on multiple lights it's possible to fine tune the shadows (contrast) by varying the intensity.

 

[Overread]

Light might behave differently, but that's more a physics question and beyond the limits of most photography that you'll undertake.

For your question in relation to photography if you have a single light source and increase its power you will, as a result, increase the amount of shadowing that it creates yes. A brighter light means stronger shadows as you are increasing the dynamic range of the scene (the range between lightest and darkest points). As a result you will have to adjust the camera and the typical bias is to react to the increase in light; thus as you expose more for the brigther areas the darker ones get darker.

That said the other property is the harshness of the light source itself and that is related more to size than intensity of light. Note that size is in relation to subjectsize as well.
Thus the sun, a single big bright light source; will give a very harsh light when at around midday on a normal sunny clear day. The light source is small and the power strong so the shadows become very sharp and dark. In contrast if its very cloudy the light is scattered out by the clouds; thus the clouds become the light source in relation to the subject and the clouds being bigger means that the light is significantly softer. The dynamic range might be the same but the edges of shadows will be more diffused than sharp.

Note that many forms of diffusion also result in light scatter and thus light loss; some mistakenly attribute light loss to the softening of the light, but its a mistaken understanding. The softness comes from the size rather than the intensity of the light source itself.

 

[fmw]

Sorry if this is a dumb question, but will light act differently as it becomes brighter? I've read books on the behavior of light but I either missed this answer or it wasn't in there. I'm mostly asking out of curiousity, I don't have any practical need for this information. I suppose I could set up a little test and find out for myself, but I love hearing you all share about this stuff. I usually learn more than I asked for when I come here.
Let's say I have a 20 watt bulb behind a diffusion panel near a face, with some space and a back drop behind the head, and the face is properly exposed at whatever the camera settings may be... If I swapped it for a 40 watt bulb (assuming, but completely unsure if this is how wattage ratings work, that the brightness doubles) and then I either dropped the ISO, closed the aperture, or sped up the shutter by one stop, would I only see the the changes that would occur within the camera (like a wider DOF or less noise) or would the light itself behave differently?
I'm assuming any other ambient light in the room would of course appear darker in comparison to the brighter bulb, maybe creating more substantial shadows, but will the main light be harder or more specular than it was when it was dimmer? I keep imagining the light acting like water or air coming out of a hose, push more out and it'll smack into stuff with more force, bounce around more, get all erratic, but I have no idea if that is incorrect.

Thanks for reading.

Light behaves like light. Dark shadows result from a light source that is small compared to the subject. Outdoors on a sunny day is good example of this. Shadows become lighter as the size of the light source increases relative to the size of the subject. A Hazy day outdoors is a good example of this. The behavior of light has nothing at all to do with it.

If you want softer light you need to increase the size of the source relative to the subject. That is why studio photographers often use devices such as umbrellas and soft boxes that serve to increase the size of the light source. Another approach is simply to put the source closer to the subject. That will also increase its relative size although perhaps not enough to make a difference.

If you increase the light output you increase exposure so you need to adjust something to maintain the exposure you want. Hope that helps put things into perspective for you.

 

[pixmedic]

brighter light has more fun than darker light.

 

[astroNikon]

If you increase the brightness of the bulb "one stop" then you compensate with the camera to 1 stop also. For simplicity, if you are at ISO 200, drop it to 100. OR Aperture F/2.8 take it to f/4 .. or Shutter of 250 take it to 500. Assuming you want the same exposure.
==> What is a "Stop" of Exposure in Photography? | Photography Mad

Also keep in mind as you increase the brightness of the light you can also increase the reflection, and may blow out some areas due to the brightness.

To compensate that you deal with the diffusion, multiple diffusion panels, distance to subject, angles in relation to reflective bounces, etc.

Don't think of light as what "you see" but what "hits the subject"
This depends upon the type of light bulb.
If you have a flood light this projects the light forward.
A regular bulb light projects the light in 360degrees, but the light hitting the subject (excluding reflections) is only a small part of that.
A CFL only a really small portion of that bulb actually projects the light "forward", the rest is scattered at all sorts of angles away from the subject.
If the bulbs are in projectors/reflectors then more reflected light gets pushed out the front.

A bare bulb ends up lighting a room (which is what a lightbulb is good for). Then you get reflections off the room walls, ceiling etc .. hoping that the "white" from that reflection matches everything else.

Also if you have the background lit separately you have to be careful on the amount of power, distance to subject, etc. For instance if you blow out the background to make it pure white, if the subject is too close and the light gets reflected back to the subject you can blow out the edges of the subject and lose edge detail.

that's why we recommend ppl get books on the subject. So much to it. ==> https://www.amazon.com/Light-Scienc...91635&sr=8-1&keywords=light+science+and+magic

 

[KmH]

Watts is a measure of how much light a source uses to produce light, it isn't a measure of how much light is produced.
How much light is produced is measured in lumens.

As alluded to in posts #4 & #6 the dynamic range of the scene your wanting to shoot will change (become broader) and you would likely want to increase the size or type of your light modifier.
You may also need to consider the dynamic range your camera is capable of capturing.

If you don't already have it, the last 3rd of this inexpensive and well regarded book would likely be beneficial to you.
The first two 3rds of the book will give you a better overall understanding of the fundamentals of photographic lighting.
Light Science & Magic: An Introduction to Photographic Lighting

 

[petrochemist]

At any light levels you're likely to be able to use the physics light obeys will not change.

It is possible for intense light to behave slightly differently in chemistry as the first photon can be absorbed & then another one hit before the very transient excited state can decay. It is speculated that this sort of effect is responsible for the trace of infra red vision that's been observed in humans. Where the IR photons are not energetic enough to trigger the visual system, but two arriving close enough together can add their energies. A similar situation in reverse (unexpected relaxation) may be responsible for the recipricality failure seen with film in low light levels.

In your hypothetical situation if both bulbs use the same technology watts should give a reasonable idea of light output (definitely not the case if the technology changes eg CFL vs halogen). Provided the ambient light does not contribute significantly the 40W lamp would give 2x the light of the 20W & so a stop smaller aperture can be used.

 

[table1349]

Light Science & Magic.

 

[smoke665]

"but will the main light be harder or more specular than it was when it was dimmer?"

In reading the Andrew's previous posts on this forum and this one, I think he understands exposure, and isn't asking for advise on adjusting the exposure for the light, but rather are there specific changes to the characteristics of the light itself, based on intensity. While everyone has seemingly touched on bits and pieces to the answer, it appears that Overread and Petrochemist have provided the most relevant answer, at least in my mind.

 

[SCraig]

... Provided the ambient light does not contribute significantly the 40W lamp would give 2x the light of the 20W & so a stop smaller aperture can be used.

Not necessarily. Grabbed a lamp at random from my GE lamp catalog: GE Halogen PAR 38 Lamps - 45 watt HIR XL lamp = 600 lumens (Initial); 90 watt HIR XL lamp = 1470 lumens (initial). Twice the wattage = 2.45 times the light level.

The wattage of a lamp has nothing to do with the lumen output of the lamp and can't be used to calculate overall light levels. You have to use the lumen output of the lamp.

 

[Derrel]

One thing you might very well notice in a practical sense is that if you move up to a fairly powerful light, like say 400 to 800 Watt-seconds from say, a Speedotron studio flash system, that once you get into that power range, there can be a LOT of ambient spill in smaller rooms, and it will act as a fill light, with fairly soft shadows. This is especially true in small,low-ceilinged rooms, like apartment living rooms or bedrooms, or in say bathrooms or in small kitchens, etc.. The difference between say a cheap, low-powered speedlight being bounced off of the ceiling, and say a Speedotron M11 light with an 11.5-inch metal, 50-degree beam spread reflector is pretty noticeable. In one scenario, you might get f/5.6 at ISO 400...in the studio flash scenario, you might get f/11 at ISO 64...in other words, a LOT MORE light can change the picture.

AstroNikon is sort of touching upon the practical aspects of less light vs. more light in Post #6...there **is** a difference between having JUST enough flash lighting to make an image, and BLASTING a big,powerful flash off of multiple surfaces within the immediate area. Like I said, a speedlight at say, an estimated Speedotron power equivalent of 45 Watt-seconds, versus what Speedotron calls "400 Watt-seconds" is a major,major,major difference in the amount of light that you have to work with...with one light level, you get a very minimal-sized impact on say a ceiling; with the studio flash, you get wider beam sprerad, and a LOT more light, and have, well--different lighting to work with.

In a practical sense, I've seen this effecr many,many times: In a small room, with one 400- watt-second flash shot into a shoot-through umbrella, you'll get 60% of the light going through the umbrella, and the other 40% bouncing off the umbrella, and creating ambient spill which can easily lighten-up and soften shadows...using an inexpensive, small speedligtht, with 1/10th the flash power in Watt-seconds, there is literally NOT much light that adds fill and so the lighting ratio will be higher, and the lighting more-contrasty. Especially common in low-ceilinged rooms or confined areas, once you start realllllllllly upping the flash power, you create a different lighting scenario than with low-power light!

In a large-sized room, there will be basically ZERO ambient spill for softening of shadows.

 

[petrochemist]

... Provided the ambient light does not contribute significantly the 40W lamp would give 2x the light of the 20W & so a stop smaller aperture can be used.

Not necessarily. Grabbed a lamp at random from my GE lamp catalog: GE Halogen PAR 38 Lamps - 45 watt HIR XL lamp = 600 lumens (Initial); 90 watt HIR XL lamp = 1470 lumens (initial). Twice the wattage = 2.45 times the light level.

The wattage of a lamp has nothing to do with the lumen output of the lamp and can't be used to calculate overall light levels. You have to use the lumen output of the lamp.

In the earlier part of my post I did say a 'reasonable idea' rather than a direct correlation. As more power is put into a filament a greater proportion of the energy output will be in the visible range. I guess I should have clarified that again in the second portion.

The rules are not changing it's just we often don't know all the rules - or chose to ignore those that don't make a significant difference

 

[Derrel]

SNIP... will the main light be harder or more specular than it was when it was dimmer? I keep imagining the light acting like water or air coming out of a hose, push more out and it'll smack into stuff with more force, bounce around more, get all erratic, but I have no idea if that is incorrect.

My experience is that more light does not become more-specular, but creates a more-diffused, lower-ratio light, meaning softer, more-open shadows. Again, largely due to the ambient spill...that light bouncing off of more surfaces, and scrambling, and bouncing around, and creating more points of origin, and thus actually chainging the quantity and character of the light.

The difference is something I noticed when using the world's most-powerful handle-mount flash at the time, the Sunpak 622 Super...a handle-mount flash so powerful that in direct-beam tests, it is as powerful in actual f/stop needed as many Made in China 400 Watt-second monolight flashes. The Sunpak 622 Super is crazy-powerful, and emits a very audible "POP!" whenh you fire a full-power flash. Shooting bounce flash with this unit, as opposed to a Nikon SB-28Dx, I noticed the Sunpak flash gave more-diffused, softer-lit bounce flash shots than lower, normal-powered speedlight shots. In the same room.